Recommended 350 TBI mods

1. First I start with a new fuel pump  which I have listed on my ordering page  is VERY important as  the stock TBI pump is only good for a max 250hp and won’t maintain fuel pressure beyond that horsepower number and pressure starts dropping leaning out the motor which can quickly damage an expensive engine.  Plus can barely keep the fuel pressure maintained for the stock 9-12 psi much less the pressure needed for higher horsepower engines.  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 GM performance parts division  offers a performance replacement distributor. AC Delco 01104060.   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 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 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 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 at 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. or . 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 350hp 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 340-360hp this is where you should be looking at the 454 injectors and run them at the 13-15psi for their 82lb/hr flow rate.  If your closer to the 340hp, you can run them at the stock 9-12psi and still be fine for this power range.

From 360-440hp 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 20psi 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.

I have put together a custom chip with the 18 psi spring and the 155lph fuel pump to make it easier for you guys to get    everything you need at one time to get those fuel systems up to par. Listed as custom chip kit on the bottom of my ordering page.

11. 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      for 4L60 700R4 trucks.

12. 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.

13. 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 and its better than stock TBI oil pump and will save us both a LOT of headaches.

14. 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.

15. 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.

16. 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.

Product Description

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.   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 if you want that cam to last more than 30k miles.   Case 1 of 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 for a different year block.  1996+ vortec all came with a roller cam.  all the roller cam hardware needed is here.

Roller cam parts  with pushrods  and Distributor (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

Level 4 is 205/215 duration @ .050 and powerband will be 1300-4800 rpms. roller cam

Level 5  is 210/220 duration @ .050 and powerband is 1700-5200 rpms.

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.

Edelbrock cams
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 cams
Lunati 10120200   194/205 duration@ .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

Cheapy Cams

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

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 dur@.050 .443/.443 112LC
E922 214/224 dur@ .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, and 12-268-4 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.

compcams.jpg (129974 bytes)

Choose one that provides the rpm range that you want your engine to run in.  For    you 93-95 TBI trucks, I can set the rev limiter to match the redline of those cams and the    4L60E automatics, I can set the shift points to match the powerband of those cams.      All 87+ cars got roller cams but the trucks didn’t get one until 1996 (Vortec).  The    trucks have all the provisions for the roller equipment but just didn’t get the parts.

Part list for converting to roller cam should you want to go that route.

GMPP P/N 12371043 = timing chain/gears and roller cam retaining plate    kit (1st and 2nd design plates!)     GMPP P/N 12371042 = 2nd design (higher ball preload) roller lifters (16)    with (8) lifter aligners and (1) spider hold-down and (3) spider attaching bolts/washers.     GMPP P/N 10457356 = Distributor gear for use with roller camshaft.



GM Fuel injection for the average guy