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new engine rebuild plan--- would love some advice

R

riv1973

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Hey all! so we have settled on rebuilding a 1987 chevy 350 we got out of a yard. it has 80,000 miles on it. we are looking to slightly increase the HP on the motor but not sure what we would have to do computer wise with the mods we are thinking about.

all the stuff we thinking about adding are GM performance parts:

the heads we are thinking about at the Vortec heads with the part number (GM part number) 12691728
cam: part number 3896962--- hydraulic flat tappet which is used in the 350CID/ 290 HP crate engine
specs are I: 222/E:222 max lift with a 1.5 rocker 450 intake/ 460 exhaust lobe center 114 degrees
intake-- for the vortec heads--12496821
rocker---12495490 ( these are stamped steel 1.5 ratio rockers.. could also go roller tip with the same ratio)
replacement TBI:

Holley OE Replacement Throttle Bodies 502-5​


my question is if all this will work well together and what we would have to do to the computer to make it all run well. we are looking to get 275 hp with about 330 lbs of torque. we are going to run a NV3500 manual behind it so we don't want anything too crazy.

and help would be appreciated. also is there anyone on the site that has a business where we can get any of the computer mods that need to be done?

thanks!!!
john
 
Roller tip rockers will do 0 for you

Vortec heads either need self aligning rockers, or guide plates
You are on or over what those rocker studs would take before they push out. Consider screw in

The factory prom will adjust about 10% variance for a TBI, then you need a new PROM. So the computer friendly cam is a good idea.
If you’re gonna burn a prom, go for it. I chose less cam and had to burn one

Later TBI had more compression. That base prom may be a good idea
 
is my cam ok for the stock prom? i guess that is my main question.

i would like to stick with the stock prom if i can. wondering if a stock cam for the 1988 K5 blazer 350 would go with the vortec heads and intake. that may be the easiest. we can also just do a stock rebuild of it all and leave it alone. just wondering if the vortec heads and intake would add a nice bump in power for little fuss.
 
The 88 cam will with with the vortec stuff. I haven’t had time today to look at that cam yet

Ideally, I’d get a prom and roller cam and use those heads. The prom from Howell is relatively cheap
 
Roller cam recommendation is more then just for performance. The flat tappet lifters available these days are huge gamble. Do some research on the subject.
Roller cam $$ might be daunting up front cost, but how many $$ to do a engine 2x?
 
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Wes Harden said:
Roller cam recommendation is more then just for performance. The flat tappet lifters available these days are huge gamble. Do some research on the subject.
Roller cam $$ might be daunting up front cost, but how many $$ to do and engine 2x?
Click to expand...
been seeing roller cams going south now . most are retro fit ones with linked lifters .1 was a local buddy of mine under 500 miles on a howards cam and broke a pin for the link bar and rolled the lifter sideways and wiped out the cam . another was online video just uploaded and not sure of brand but same problem and lifters looked identical in design .

if going roller cam check to see if your block will take stock roller stuff and if so get these parts / design over aftermarket link bar stuff .

i have a whole setup here i was going to use in a 350 tbi motor but didnt . and the cam is from a LT1 350 motor so its computer compatible but stock from gm and much better than tbi cam . even have brand new comp roller tip self locating rockers . pm me for a deal if you want it all . i dont need it anymore .
 
Vortec heads certainly will not work effectively with stock TBI PROM.

Your numbers (IIRC) are right around what the stock L31's put out. Given I'm running an L31 long block...as I've said multiple times, fueling and timing is WAY off from what "old school" GM heads wanted.

Narrowband O2 sensors (all OBD1 I'm aware of) do not "actively" allow compensation under load for fueling. There is no feedback that the system is X air/fuel ratio when under load (or when the engine is cold). If it's running lean under load? Your first clue will be knock. The system can retard timing, but that is after knock starts, and means you are losing power when you need it, not to mention the obvious, the engine is knocking.

Note that apparently the TBI motors require ridiculously low amounts of timing, and Vortecs take considerably more. Even barring fuel as an issue, lack of timing makes an engine a dog.

You can try to increase fuel pressure via an adjustable regulator, but that's going to increase fuel at all points, so it's likely you'll end up rich when you don't need it. Vortec heads and a cam are not mild upgrades.

If you want to try it without budgeting in for chip replacement, your choice.

Numerous similar threads on thirdgen. https://www.thirdgen.org/forums/tbi/587248-another-tbi-vortec-question.html
 
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So i have not done a build on a truck of this vintage before. It seems best to just stick with stock?

Even if I planned to go with the vortex heads the prom will need to be changed is they correct? And are there proms to buy that are based on what I add for mods? Or are they pre programmed for what we are going to do?

Also how does aftermarket fuel injection set ups work? Do they remove the old computer stuff and add their own fuel mapping software?

We are looking for a simple rebuild so we may just stay stock. We are going to have to rebuild the heads but was looking to see if we could add better flow and keep the cam stock to slightly increase power. I am gathering a cam Change is a bigger deal than I thought.
 
Changing the cam and compression add the most power

The portion change would get the most out of your changes


Are you using an automatic with a lockup?



When I had Howell burn a prom for me, they deleted all of the unnecessary stuff including the vehicle speed sensor and lockup details. The Tbi works just fine without the vss
 
If you’re not needing a lockup, the aftermarket Efi is fine. When you need the lockup, it becomes more expensive
 
Some reputable companies *might* have PROM data saved from similar engines/builds. But there are a lot of differences to get it "right". Gear ratio, transmission, engine displacement, all matter in the tune even from GM.

TBI is old tech, and it's getting hard/costly to modify it. Aftermarket FI generally incorporates all the tools and tech to get a system to work with what it's installed on. But if that's a direction you want to find more about, you'll want to seek opinions on those various systems.

Personally I think TBI is great if everything stays bone stock. Beyond that, anymore, aftermarket solutions make a lot of sense. Or LS. But that's another can of worms.
 
80,000 miles….stick it in the truck and run it. It’ll never be as reliable as it is right now with the quality of aftermarket parts anymore
 
thanks guys!em

i think we will have the heads redone ( redo the valve seats and clean them up) and put the motor back into the truck. we will have the short block inspected after we tear it down to make sure it is in good shape. the only thing i may consider is a Vortec head swap with the Vortec manifold for TBI. all from GM itself.

has anyone run the aftermarket Holley TBI unit? i think it is the Holley replacement TBI 502 unit. it is about $850. was thinking this might be a good upgrade.
 
riv1973 said:
thanks guys!em

i think we will have the heads redone ( redo the valve seats and clean them up) and put the motor back into the truck. we will have the short block inspected after we tear it down to make sure it is in good shape. the only thing i may consider is a Vortec head swap with the Vortec manifold for TBI. all from GM itself.

has anyone run the aftermarket Holley TBI unit? i think it is the Holley replacement TBI 502 unit. it is about $850. was thinking this might be a good upgrade.
Click to expand...
buy some better vortec heads aftermarket off the bat and be done so later upgrades are ready to bolt in .

but if changing nothing else in the short block the heads wont get you much at all. . stock TBI cam is a TURD for power and almost any cam is a upgrade .

call howell ..... talk with the chip guy ...... make a plan from there on what he knows works .

i will be listing a bunch of stuff soon for tbi or sbc upgrades . so keep a eye open and maybe some will work for you .
 
sweetk30 said:
buy some better vortec heads aftermarket off the bat and be done so later upgrades are ready to bolt in .

but if changing nothing else in the short block the heads wont get you much at all. . stock TBI cam is a TURD for power and almost any cam is a upgrade .

call howell ..... talk with the chip guy ...... make a plan from there on what he knows works .

i will be listing a bunch of stuff soon for tbi or sbc upgrades . so keep a eye open and maybe some will work for you .
Click to expand...
If he’s gonna spend that kind of money, buy aftermarket heads new…
 
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