1. First I start with a new Fuel pump, STOCK 75lph TBI fuel pump will only support about 230hp before the fuel pressure drops like a rock. I recommend upgrading to the 1996 Vortec 155lph fuel pump which can support up to 450hp and plugs right into a factory TBI sending unit. https://www.summitracing.com/parts/ado-ep381 So I begin every project with a new upgraded pump.
2. Exhaust, You need to start there because doesn’t matter how much you improve the air going in, if you can’t get it out it will run poorly and the stock exhaust is terrible. Well the KEY issues with the exhaust is the Y pipe and the catalytic converter. GM intentionally made that Y pipe restrictive to increase back pressure and most have paid someone to spread a myth that back pressure in the exhaust is GOOD. Its NOT. Air velocity is good not back pressure. The reason for the back pressure was so that the EGR smog system would work better and the increased pressure would build up a lot of heat to keep the o2 sensor hot. A good free flowing exhaust does typically need a 3 wire heated o2 sensor conversion to maintain its temperature. To fix 90% of the exhaust issues, I recommend a Flowmaster Y250300 collector from your favorite vendor and replace that section of Y pipe where the 2 pipes merge. Dramatic improvement over that stock GM design. As for the cat, I know most say it should fall off and turn a blind eye but I personally don’t like the smell of the exhaust with no cat and want to do my part towards our environment as well. you can search ebay for THUNDERBOLT 3 CATALYTIC and those high flow cats are like $50. As for headers, not really recommended on engines under 300hp and for muffler, you want an aggressive sound that’s fine pick from several. I have been using a FULL BOAR SS muffler off ebay which are stainless and cheap and flow well but not going to be a huge gain in power. the Y pipe will add a noticeable amount though and will help support more modifications.I clipped this picture from my latest Hot Rod magazine on choosing the size of your exhaust pipe.
3. ignition. People either skip this entirely, or skimp on the parts used or go crazy. TBI is a simple injection system. KEEP IT THAT WAY. No MSD or other ignition boxes. That just makes diagnosis harder and have yet to see any gains on this system from adding one. First, if the distributor is out for cam swap or engine replacement then change the pickup stator with a new AC Delco D1987 pickup stator. you can order those from nearly any auto parts store. I only use AC Delco electrics as most all others is poor quality chinese parts. AC Delco still chinese but have better handle on quality control. If your distributor has over 100k miles on it. REPLACE IT. You just asking for a headache that neither of us need. So what to use. For roller cam engines use a new best brand distributor you can get at your local autoparts store for a 1992 Camaro 350 TPI Z28 which also uses a flat tappet camshaft. For flat tappet cams, I recommend the Davis Unified 12620bk then for Plug wires, if your running a stock engine then stock replacement wires are typically fine but any decent peformance engine USE A BETTER WIRE. I like the Accel 5114K as they are not only nice low resistance wire but the outer casing of the wire is tougher than any other wire I have used and the price isn’t bad. For coil, up to 4500 rpms stock coil just fine. If your going to rev her on up then I recommend a Pertronix D3002. Good coil for the money. Too many issues with the MSD and Accel coils to recommend them lately. For plugs AC Delco again seems to give me the best plug coloring. R44TS for stock iron heads that use .500 reach plugs or R44LTS for .750 reach plugs for vortec heads and aluminum heads. Some of the aftermarket iron heads take the .750 reach plugs now so check that out when you order your heads.
4. The cam in the TBI engine is just plain AWFUL. Specs on Stock TBI cam is .050″ tappet lift (intake/exhaust) is 165/175; and maximum lift with 1.5:1 rocker ratio (intake/exhaust) is .382/.402. I got those specs right off the Jegs website selling the new GM replacement TBI crate engines. Valve springs are also VERY important due to the stock ones having a redline of 4500 rpm. I have run these engines with better cams and stock valve springs up to 5000 rpms with no issues but its not going to be recommended. Cam, stage 2chip and exhaust mods are going to net you a good 50-60hp on that pathetic stock 180hp 350 TBI motor. (factory 210hp rating was a bit optimistic from my dyno testing) cam choice in my opinion is the most important decision you make on that engine as its not only the easiest way to screw up TBI injection but it also sets the whole attitude for how that engine is going to run and whether it has good low end power or strong mid range or strong top end power. I have listed a bunch of new cams at the bottom of the page. This should provide you with a sufficient assortment of cams for whatever power range you want for your motor. If you still don’t know what cam to use, email me at [email protected] all of your engine and vehicle details and I will gladly recommend a cam for you.
Roller versus flat tappet cams. All 1987 blocks have the provisions for the roller cam just the trucks didn’t get them. However in some 93, all 1994 and 1995 engines GM stopped drilling and tapping the bolt holes in the those provisions in the block. Roller cam will give you the same power as a flat tappet cam that is about 15 degrees duration bigger or about 10-15hp more than the same duration flat tappet cam. This allows you to run a milder roller cam that gives you better low end torque and horsepower and have the same peak horsepower as a cam that will have weaker low end power. If you can afford to go roller, GO ROLLER.
5. Rocker arms. I have had a lot of questions about rockers and I have had a lot of customers having issues with all the cheap rocker options. So I no longer recommend changing the rockers on TBI motors as the amount of power you gain on these mild engines isn’t going to justify spending $300 on quality roller rockers.
6. The Heads. The TBI heads are the worst flowing heads GM ever released. If your rebuilding the motor, don’t waste ANY money on those pitiful poor flowing TBI heads. Valve springs and a good magnaflux and valve job will cost you a couple hundred or more and that money could have been spent on decent new heads. So the best bang for the buck is GM Vortec head but does require a special intake and lots of EGR work if you need EGR to remain emission legal. These heads are good for a minimum 50hp gain. Just be careful with used Vortec heads as they are prone to cracks after 100k+ miles of heat and cooling cycles, iron cracks. Another good reasonably priced set of heads that will work nicely without special intakes on a TBI motor is a set of Summit Racing aluminum heads. Great flow number and stock TBI or aftermarket TBI intakes will bolt right on saving you some money. 50 state legal and better flow numbers than vortec heads. Manufactured by Trick flow for Summit.
Flow data for Summit heads at 28”
Lift intake / exhaust
.100 70 50
.200 136 90
.300 183 124
.400 222 151
.500 242 175
Lots of head options out there now and changes all the time. Be careful of the chinese junk out there as well. Saving a buck can lead to a lot of headaches diagnosing issues and money thrown at changing parts trying to solve the issue. When chosing heads its important to know the flow data for those heads and not to choose a head with too much intake runner. While a 210cc intake runner head will make good horsepower on a 350 engine its not going to make good low end torque. now with a 400ci SBC that 210cc intake runner will work just fine as you have 50 more cubes to pull air down that runner. On the average 350, I like a intake runner in the 165-180cc range and I like my air flow at .500″ lift to be at least the 225cfm that a vortec head flows. Stock TBI head flows around 175cfm. While .500″ lift numbers don’t cover all the aspects to look for such as lower lift flow numbers and exhaust flow numbers its at least something to help you chose a set of heads. If its a GM head you have google the casting number with FLOW behind it and you may find some flow data for that head.
7. The air cleaner. I recommend a little easier route than I used to. open element filters are fine but you can just put http://www.summitracing.com/parts/knn-ce-1503 and cures nearly all the air flow issues with the air intake. if you have the dual stud lid those studs easily come out of those bolts and you can use http://www.summitracing.com/parts/spe-4215/overview/ as your throttle body has the provision for it.
8. Modify the throttle body. This one pretty cheap but does require removing the throttle body. UTIMATE MODS. Stock 42mm TBI units flow around 450cfm which if you look athttp://www.carburetion.com/calc.asp a stock 350 even with a cam upgrade to increase the powerband to 5500 rpms isn’t going to use much if any more than that stock throttle body. But you can do those ultimate mods since they are free and will give you good air flow up to about 270hp or about anything you can build with the stock TBI heads.
If your going going to build a motor for over 270hp then you need more then the ultimate mods. Have one of these 2 companies bore your stock throttle body out for more air flow. www.rvmorsemachine.com or www.tbiparts.com . I DO NOT recommend the Holley aftermarket TBI unit but have been plagued with bad injectors and base casting issues so I don’t recommend using one. I also don’t recommend a 454 TBI unit as they were designed to idle big block engine and often cause idle and light throttle fuel control issues on SBC so save yourself and me some headaches and get a bored SBC throttle body.
9. Injectors. EVERY BODY wants to change injectors. That’s fine but these injectors are not power adders and only need enough fuel to mix with the amount of air your motor can suck in. All these TBI injectors are over 20 years old and have a lot of wear on them. 454 injectors are the worse for having poor low duty cycle issues causing poor fuel control at idle and light throttle. The odds of getting a GOOD set that will work in a SBC is slim so I have been just cranking fuel pressure up on the 350 injectors on most SBC applications. Those making 375hp or more do have to resort to 454 injectors though.
Instead of using adjustable fuel pressure regulators which has been all the rage in the past. I have tested several springs and had a custom spring which I have listed on my ordering page. made that will yield 17-18psi at a much lower cost than buying a regulator and a fuel pressure gauge to set that regulator by. This way you can just slap the spring in and go and its a one time disassembly of the throttle body instead of 3 or 4 times to get the fuel pressure correct. However stock wimpy fuel pump is not going to pump 18psi and your lucky if it will hold 12psi once those injectors spray enough fuel to support a 250hp motor.
So what size injector or fuel pressure combo to use? Well here is a basic guideline.
Stock 210hp 350 V8 up to 250hp the stock 55lb 350 truck injectors at the factory 11-12psi is fine.
from 250hp to 260hp the fuel pressure should be bumped up to 13-14psi on stock 350 truck injectors which will change their flow rating to 60lb/hr
From 270hp to 340hp you need to change the fuel pump as the stock pump can’t maintain pressure over 270hp and you need to run 18psi on the 350 truck injectors for a flow rate of 72lb/hr
From 340-370hp this is where you should be looking at the 350 injectors and run them at the 22psi for their 82lb/hr flow rate. If your closer to the 340hp, you can run them at the stock 18psi and still be fine for this power range.
From 370-440hp you need to bump the fuel pressure up on the 454 injectors to the 15-18psi to increase their flow rate to 100lb/hr.
For over 450hp you really should be looking at alternative injection system but for up to 450hp you would need to run nearly 22-26psi of fuel pressure to increase the lb/hr rating on 454 injectors to 112lb/hr and that is as much pressure as I recommend applying to a set of TBI injectors.
10. The chip. Depending on how many of these modifications you do the more the need for a custom chip or chips. But a chip will give you the most bang for the buck of any mod you can do to the vehicle.
11. I really should move this higher on the list. its typically the FIRAT thing I change on a TBI vehicle but then I have to renumber the whole page.
12. Gears. One of the best ways to get the power to the ground is through gearing. A 3.73-4.10 gear makes a nice streetable rearend gear. Some of the trucks came with 2.73 and some with 3.08. These are terrible gears. I feel that the 3.42 gear is tolerable in a 2wd especially if its pretty stock. check out the speed calculator on this site on left menu and play with that calculator. I like my trucks to run around 2000-2400 rpms at 70mph in overdrive. Less than 2000 and you don’t have any power in overdrive and it just shifts to 3rd at the least little thing. Over 2400 will make more power but gas mileage will suffer. In that range and the gas mileage will be fine. For speedo calibration for a tire and gear change go to the menu link for VSSB Calibration for 4L60E,4L80E or 5spd trucks and http://www.transmissioncenter.net/speedometer_calibration_______va.htm for 4L60 700R4 trucks.
13. Torque converter for you automatic lovers. The stock V8 converter stalls at 1400 rpm which is very low. The 95+ S10 4.3L V6 torque converter stalls 2000-2200 rpm. That 600 rpms will help keep your engine in its powerband and thus make it faster. If you go with a cam with over 212 duration @ .050″ (which I don’t really recommend with TBI anyway) then a higher stall would be advised for most street applications. The 2000 stall is a good upgrade that won’t screw up your gas mileage, burn up your trans, break the budget, or be unbearable on the street.
4×4 guys, I typically don’t recommend the higher stall converter. If you go off roading that extra converter slippage can be a nuisance.
14. Oil pumps, I have decided to add this on the list as TOO many people when building engines put high volume oil pumps in their motors and don’t do this for a few reasons. 1. you would need to run a 7qt oil pan or you will suck the stock pan empty with any spirited use. 2. It takes 20hp to turn a high volume pump at higher rpms over a std volume pump. 3. Unless you prep the block properly you will end up sending too much oil to the hydraulic lifters and pump them up too much causing vacuum issues and poor performance. I use a std volume, high pressure pump http://www.summitracing.com/parts/MEL-M55A/ and its better than stock TBI oil pump and will save us both a LOT of headaches.
15. Never thought I would need to put this on here but just too many issues with these items to ignore. Avoid Bosch o2 sensors, for some reason they cause problems with TBI systems. I haven’t figured out why they work differently yet but until then, I recommend avoiding them. Next is spark plugs, Avoid the fancy plugs like the Platinums and E3 plugs for some reason they don’t work well with TBI either. I haven’t found anything better than a good old AC Delco R44TS or R44LTS depending on which plug length you need for your heads. Most aluminum heads and the vortec heads require the longer LTS plug where the TBI heads and most old iron heads use the shorter TS plugs.
16. I had a customer email me this link asking about it so I thought I had better post it on here. Biggest waste of $900 that I have seen for TBI. Crappy Holley throttle body stuck on a stock edlebrock intake with unmodified 42mm bores in that intake which isn’t going to let near the airflow in that the 52mm Holley TBI has to offer even if the Holley throttle body wasn’t so bad. http://www.jegs.com/i/Edelbrock/350/3704K2/10002/-1
17. PCV Valves. A customer recently did some research on this after having issues with his engine and so I feel its something, I need to mention. most of you if you have a 350 and you go to a mild 350 upgrade will be fine with a stock 350 PCV valve. if you went from 4.3L or 305 to a 350 then you certainly need to change it as they are different. now if you have a 383 or 350 with at least a level 5 camshaft then you may need to use the PCV valve that GM uses in their ZZ383 crate engine.
GM Performance ZZ383 engine is recommended to use GM # 6487779 PCV valve, which cross references to Purolator # PV774.
This PCV valve functions better with the lower vacuum signal of a performance engine using a camshaft with more duration and overlap.
PCV valves are not all calibrated the same, and perform differently depending upon the amount of vacuum an engine produces. A performance camshaft will typically produce a lower vacuum signal than the stock engine/camshaft, and the stock PCV valve may not close enough at idle, which can cause an irregular and/or high idle, or otherwise not function efficiently throughout the operating range of the engine. An improperly functioning PCV valve can also cause the premature break-down of engine oil, sludge build-up, leaking gaskets and seals, water vapor build-up, as well as allow excessive oil to enter the intake manifold. A PCV valve that closes too easily and completely, can stay closed too long above idle, and can also interfere with the proper evacuation of blow-by gases. This PCV valve functions better at a lower vacuum signal, but still opens once the engine vacuum changes during all-around operation. PCV valve starts to close ~1-2 in-hg
NOT USING THE CORRECT PCV VALVE will give driveability problems as well as oil leakage problems and consumption problems!!!!
I hope that this info is helpful.
FIRST flat tappet cams are problematic at best and if you even want a 30k mile life span from one you have to add zddp to your motor oil. http://www.jegs.com/i/Eastwood/352/12269Z/10002/-1 for that old obsolete cam technology as modern motor oil no longer has zinc phosphate added to it. no such thing as a good flat tappet cam as they are problematic, obsolete technology that requires using ZDDP additive https://www.summitracing.com/parts/isk-zddp if you want that cam to last more than 30k miles. Case 1 of http://www.kirbanperformance.com/product_images/customer_support_item-_pdf-35.pdf is the important one. The only reason the stock camshaft lasted as well as it did was the very low duration and lift of the cam as well as the very weak valve springs. Once decent valve springs and decent cam are used the zinc issue becomes and issue.
So I really never recommend a flat tappet cam in a new engine build. Its ok to toss one in a motor with some mileage on it but with a new engine. GO ROLLER. 1987-93 blocks have all the roller cam provisions. 1994-95 GM did stop drilling and tapping those provisions so I typically wont rebuild one of those motors. I will search craigslist or car-part.com for a different year block. 1996+ vortec all came with a roller cam. all the roller cam hardware needed is here.
Roller cam parts http://www.summitracing.com/parts/NAL-12371042/ http://www.summitracing.com/parts/NAL-12371043/ with pushrods http://www.summitracing.com/parts/hrs-95201 and Distributor https://www.summitracing.com/parts/ado-1104060 (for roller cam)
Levels of cam. I am going to list as 6 different levels of camshaft that you can run with TBI.
LEVEL1 is stock cam which is 165/175 duration @ .050 and has a powerband of 0-3200 rpms.
Level 2 is going to be a duration of around 185/195 @ .050 and powerband will be 500-3800 rpms.
Level 3 is duration 195/205 @ .050 and powerband is 1000-4500 rpms. example for roller cam https://www.summitracing.com/parts/nal-14097395
Level 4 is 205/215 duration @ .050 and powerband will be 1300-4800 rpms. roller cam https://www.summitracing.com/parts/cca-08-409-8
Level 5 is 210/220 duration @ .050 and powerband is 1700-5200 rpms. https://www.summitracing.com/parts/lun-20080660
Level 6 is 215/225 duration @ .050 and powerband is 2000-5500
Use the speed calculator on the website. DO NOT choose a camshaft that is going to put your engines powerband at or below that bottom powerband number at your cruise speed of lets say 70mph in high gear. this will make for a miserable performing engine. Stock gearing is designed for that stock cam to put that power range right in the middle of the cams powerband. you dont have to be quite that drastic but on level 4 – 6 cams you need to be geared to run a good 300 rpms better than that bottom number @ 70mph. Ignore that recommendation and dont say I didnt warn you.
TBI computer does not do well past 5k rpms so some of the cam choices have been adjusted.
SummitPart Number: EDL-3702 Basic Operating RPM Range: Idle-4,000 Duration at 050 inch Lift: 194 int./214 exh. Advertised Duration: 244 int./264 exh. Valve Lift with Factory Rocker Arm Ratio: 0.398 int./0.442 exh. lift Lobe Separation (degrees): 112
Summit Part Number: EDL-2102 Basic Operating RPM Range: 1400-4,800 Duration at 050 inch Lift: 204 int./214 exh. Advertised Duration: 278 int./288 exh. Valve Lift with Factory Rocker Arm Ratio: 0.420 int./0.442 exh. lift Lobe Separation (degrees): 112
Lunati 10120200 194/205 [email protected] .050 .405/.427 112 LSA 1200-4600 rpms range
Lunati 10120203 204/214 dur. @.050 .420/.442 112LSA 1500-4800 rpms range
Lunati 10120700 207/213 Dur @ 050 inch .437 int./.454 exh. LSA 112 rpm range of 1800-5000.
Lunati 10120701 213/219dur @.050 .454 int./.468 exh. lift LSA 112 rpm range 2000-5200 rpms
Lunati 10120702 219/227 dur @ .050 .468/.489 LSA 112 rpm range 2200-5500
Sealed Power cams
CS1014R 1500-4800 RPM Range 278 intake/288 exhaust Adv Dur Duration @.050 204 intake/214 exhaust Valve lift 420 intake/443 exhaust, Lobe C/L 112 Strangely this cam has the exact same specs as a Summit 1102 HMM wonder who makes Summits Cams, Also looks exactly like the Edelbrock 2102 cam.
CS1105R 1800-5000 RPM Range 283 intake/286 exhaust Adv Dur Duration @.050 209 intake/216 exhaust Valve Lift .435intake/.455 exhaust Lobe C/L 112
Also Northern Autoparts Northern Auto Parts has the sealed power cams complete with timing chain and gears as well as the cam and lifters as a kit for under $100. Can’t beat that for a budget build.
Elgin cams available from competitionproducts.com
E1100 184/194 duration @ .050 .368/.398 104LC
E1127 190/200 dur. @ .050 .385/.408 112LC
E247 194/203 dur. @ .050 .390/410 116LC
E1005P 194/204 dur @ .050 .398/.420 112LC
E860S 202/207 dur @ .050 .404/.414 114LC
E923 204/214 dur @ .050 .420/.443 112LC
E1128 208/208 dur @ .050 .420/.420 110LC
E1029 214/214 [email protected] .443/.443 112LC
E922 214/224 [email protected] .050 .443/.454 112LC
E1166P 216/228 dur @ .050 .453/.480 112LC
COMP CAMS I have not edited those pictures yet but the 12-262-4 and 12-236-3 are a level 6 camshaft and level 7 12-404-4, and12-268-4 are no longer recommended because the TBI computer system just seems to fail to make any power above 5200rpms. So the problems generated below 1500 rpms does not gain you any additional power on the top end from running a larger camshaft and causes way too many idle and stalling issues.
As you can see below as the duration gets higher so must the lobe separation angle.
Join Date: Jul 2003
Location: Indianapolis, IN
Best heads for TBI conversion
I am looking at installing TBI on the 73 vintage 350 that currently currently resides in my 86. My current options for heads are:
1. Modify the stock 87 tbi intake to work with the "492" double hump heads currently on the engine.
2. Rebuild a set of 87 tbi heads and install them.
3. Rebuild a set of "906" Vortec heads and install them.
4. Install a set of "083" L98 heads.
I drive the truck everyday and use it as a truck on the weekends, so driveability and mileage are as important as performance. The engine has cast 9.5/1 replacement pistons, headers, and a mild hydraulic cam with around .442 lift.
Any opinions or comments? Thanks.
Last edited by beaterC10; 09-18-2006 at 02:13 PM.
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Late 350 Chevy TBI Heads on a Carbureted 1970's Short-Block
Pit Stop - April 2013
Wendell T. Brown From Kansas City, Missouri, Asks
Q: Will Late 350 Chevy TBI Heads Work on a Carbureted '70s Short-Block?
A: I have a '72 350 Chevy engine without the original heads. Can '90 350 throttle-body injection (TBI) heads off a 1500 Chevy truck work? Some engine shops told me yes, and some said no, because of the water jackets and that they are low-performance heads, anyway. My engine is bored 0.040-over with Sealed Power pistons with 10.0:1 compression. The engine is going in my '77 C10 pickup truck. It is just transportation, not for the dragstrip.
Wendell, your heads share similar characteristics with '87-'95 iron production small-block Chevy heads (not to be confused with '96-and-later Vortec heads or reverse-cooling '94-'96 Iron-headed Generation II small-blocks). These '87-'95 heads have the same water jackets as early heads and still retain a street-carburetor-friendly exhaust heat-riser passage, but there are other differences you need to be aware of. Tony Knight of Cylinder Head Exchange, a leading West Coast cylinder-head bank for just about any domestic or foreign head, helped set us straight. Current GM Part No. information was provided by Ken Casey of John Elway Chevrolet.
Regarding physical interchange: Yes, the heads in this group physically bolt on to your existing short-block but require a unique intake manifold and corresponding intake-gasket set because the center two intake-manifold-to-cylinder-head attaching bolts are drilled at a different angle than traditional small-block Chevy heads. Most GM production cars and trucks used TBI or (on some Camaros and Firebirds) TPI (tuned port injection) manifolds on this series of heads. However, there were still some carbureted applications in '87 and '88 that had factory intakes that accept a Quadrajet carburetor and are drilled with the new intake-to-head-bolt pattern. Casey says to look for Q-jet intakes on 305 LG4 (VIN-H) engines installed in the '87 Camaro/Firebird (F-chassis) and '87-'88 Monte Carlo (G-chassis), the 305-HO L69 (VIN-G) in the '87-'88 G-chassis, and the 350ci LM1 engines installed in '87-'88 fullsize Caprice Police cars (B-chassis with SEO 9C1 or 9C6). Most of these Q-jet intakes are iron (GM PN 14101075, discontinued; Hollander Salvage Yard Interchange No. 1161), but a rarer aluminum intake was also factory-installed on some of these cars.
At one time, GM offered a marine, cast-iron, dual-plane, high-rise intake dual-drilled for both Q-jet and square-flange carbs for sale through dealer parts departments (PN 14097494), but it was discontinued in February 2010. Edelbrock lists carbureted dual-drilled (Q-jet/square-flange) Performer aluminum intakes for '87-'95 cast-iron cylinder heads (PN 2104, without EGR; PN 3706, with EGR). Another commonly chosen option is to oblong the center four holes of a standard intake, ovaling them until the bolts fit, then using wedge-shaped washers under the bolt heads.
One potential deal-breaker is the possible effect of the late heads on your engine's compression ratio. The '87-'95 cast-iron 350 heads returned to 64-66cc combustion chambers. You state that your Sealed Power pistons are designed to produce 10.0:1 compression. If that's 10.0:1 with a 64cc head, assuming decent tuning skills, you should be OK on pump premium unleaded (cranking compression should not exceed 200 psi). However, if these pistons are, in fact, designed to yield a 10.0:1 ratio with the stock 75-76cc smog-chamber heads as originally factory-installed on the '72 350 short-block or on your '77 C10's old 350 engine, there will be big-time problems: The small chambers in the '90 heads raise the compression ratio 1 to 1.5 points. Depending on the piston deck height and head gasket, that could end up as high as 11.5:1-not viable on pump gas with old-school, non-electronically-controlled engines and mild, off-the-shelf cams.
Early heads have a six-bolt exhaust flange (A); around '76'77, a seventh hole (B) was added at one end that supports heavy catalytic converters (on the passenger side) or redesigned power-steering pump brackets (on the driver side). Stock exhaust manifolds must match (headers often have both patterns). The '70s-era heads have a -NPT temp-sender boss (C); later use a 38-NPT boss (D). On early "heavyweight" heads, the deck surface below the outer row of head-bolt bosses is straight (E). Later "lightweight" heads like Brown's castings have scallops (F). Lightweights have thin decks that usually can't be milled and shouldn't be installed using steel-shim head gaskets. Late heads add exhaust wire-loom mounts (G).
Most late-'60s through mid-'80s heads have one accessory mount bolthole at one end (left) and three holes at the opposite end. Starting in the mid-'80s, both ends have had all three holes (right). In terms of accessory-mounting provisions, late heads work with early brackets, but early heads may not accommodate late brackets (including some serpentine-drive setups).
ID Chevy heads by the casting number's last three digits. The full number is cast on the valve-cover side (shown); the last three digits are repeated on the chamber side at the bottom of an intake runner. Brown's '90 12-ton truck heads should be a No. 193 casting like this. Three-quarter-ton heads had No. 191 castings; 1-ton used No. 810. Caution: 810s had valve rotators with a deeper valvespring pocket and must be heavily shimmed when using normal springs without the rotators.
Different rocker arms may be required. Heads not set up from the factory for close-tolerance pushrod guideplates had oblong pushrod guide slots broached on the valley side of the heads until about 1990, and originally used nonguided, "flat-pallet," rocker arms. After that, GM began transitioning to a new, guided rocker-arm design with a U-shaped pallet. Heads for guided rockers have large, 716-inch, round pushrod holes. The relatively rare production GM heads factory-machined for screw-in studs and close-tolerance pushrod guideplates also had either big round holes drilled through the original oblong slots or large pushrod "windows." These differences are important, because with the wrong combo, the pushrod could potentially be put into bind from trying to locate in two different places. In terms of your late heads, Knight has seen the same casting number factory-machined both ways (with either slots or holes).
Officially, GM says guided rockers can replace the earlier nonguided design all the way back to '55 and should therefore work on any small-block head. However, the early nonguided rocker can't be used on late heads machined with the round, 716-inch, guided-rocker-style holes. Even so, in my opinion, you should also not use guided rockers with any mechanical lifter and/or heads with close-tolerance pushrod guideplates.
Most '71 through mid-'80s iron production heads had large 76cc chambers, used to help drop compression for compatibility with unleaded gas before the advent of electronic engine management. Common castings in this group include Nos. 487, 624, or 882. Some of these even had 2.02/1.60 valves, screw-in rocker studs, and pushrod guideplates. The late '80s marked a return to smaller, 6465cc chambers. No. 193 is typical of most TBI '87'95 iron heads, with half the intake valve-bowl approach blocked off—not good for serious performance. One exception is the '87'91 Camaro TPI 350 No. 083 head that had full "open" intake runners. With old used heads, be sure that the spark-plug cooling "eyebrow" (arrows) hasn't rotted out to the extent it impinges into the head gasket's fire-ring bead area.
As with any '86-and-later Chevy small-block production casting, the '90 heads are machined for center-bolt valve covers instead of the perimeter-bolt covers used on older heads. If original appearance isn't a requirement, just use any of the myriad available stock or aftermarket center-bolt covers. In terms of maintaining the original appearance, Speedway Motors is one source for an adapter that allows the use of perimeter-bolt valve covers (PN 91017157).
Although you say the intended application is "just transportation," for the record and general knowledge of our readers, it is important to note that most '87-'95 cast-iron production heads have at best limited performance potential. Although the 350 versions do at least have 1.94/1.50-inch valves, nearly all variations have half the approach to the intake-valve bowl blocked off in a crude attempt to induce mixture swirl. With any decent cam, most castings in this series of heads will give up at 3,500-4,000 rpm. Knight says the main exceptions are the '87-'91 Camaro/Firebird 350-TPI head (casting No. 083, 64-65cc chamber, 1.94/1.50 valves) and its 305-TPI equivalent (casting No. 081, 55cc chamber, 1.84/1.50 valves)-both are nonswirl castings with standard-configuration intake runners. The '87-'88 Caprice carbureted 350 Police cars reportedly use nonswirl heads as well.
If performance is the main criteria, and excessively high compression with your existing pistons won't be a problem, when it comes to production iron castings, '96-and-later L31 Vortec heads (casting Nos. 062 or 906) are superior to any earlier factory design, even '60s muscle car-era heads. However, Vortec heads have additional interchange issues beyond the scope of this discussion.
If large-chamber (75-78cc) heads are needed to keep the compression ratio under control, you'd be better off with commonly available late '70s No. 882 castings. They're a direct replacement for your model year, with the right intake-manifold bolthole angles, combustion chamber size, valve-cover bolt pattern, and temperature sender hole. No. 487 castings are another good choice.
Large, round small-block Chevy cylinder-head pushrod guide holes (left) are for use with guided rocker arms; oblong slots (right) were originally used with nonguided rockers. Brown's '90 heads could have been factory-machined with either slots or holes. If the heads have the round holes, Brown needs to use guided rockers to properly locate the pushrods.
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Tbi heads best
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