I have a1988 TPI 5.7 auto car. When purchased, I was told motor was rebuilt/replaced but no details available. Body had 156k miles and after changing the fuel tank, pump, and sender, It ran, not great; but enough to cruise around. It never liked full throttle, would fall on its face. Car saw maybe 200 miles in last 8 years. Fuel got stabilizer treatment regularly and when taken out of storage, tank was siphoned out and a few gallons of fresh fuel added.

Fast forward to now. Finally decided to tear into the tpi manifold and replace distributor(rusty inside) and change injectors(same from when car was bought, a lot of junk in tank).
Well while it was apart, I decided to try to run numbers to see what the motor actually was.
Block is a 350 with a casting date in 1990. Factory roller cam block so thats good. Original block would have been nice but thats fine.
Then I ran the head casting and those are "swirl port" heads basically from a 350 TBI engine, 10110810 casting.

I would like to put oem heads on it now but, does it REALLY matter? Finding a set hasnt been easy and I currently do not have the time to pull it apart more and even then I dont know what that'd lead to with finding anything odd in the shortblock. With the egr system cleaned out, TB cleaned, plenum runners and base all cleaned, fresh injectors, new spark plugs, and fresh injectors will the negative affects of those TBI heads really make a difference? I'm not going to be racing the car. I'm not going for extra horsepower. I just want to be able to drive it locally. I'm thinking now just to put it back together as it was and plan for a motor/head swap in the future.

 

Some of the "swirl" heads had radical bowl redesign, ans some were fairly moderate. The ramps (swirlers?) in the chambers and bowls intending to accelerate the fuel/air charge as it blows past the valve will tend to negate the charging effect of the TPI runner length and plenum design.

Of course it will run, but probably not as it was initially designed.

Another question arises regarding the cam profile. If the heads were not TPI design what may have been done to the valve train?

Ultimately, grabbing a pair of 14101081 original iron heads for scrap value could be worthwhile, or reasonable aftermarket heads if you can find a pair reasonably might be worth consideration.

As far as WOT operation, more than the heads will affect just how successful that will go.

 

If this was an original 350 car then it was an L98. Those had aluminum cyl heads from the vette. They are 58cc heads so they gave the l98 decent compression. Between this and the cam that the L98 engines had your current computer is probably relatively unhappy. If you have a new engine w tbi cam/heads your computer is unable to get the proper timing/AFR to run as intended. You need to either get a custom prom chip or get the parts that your current computer/chip will work with. To get a custom chip you will need some specs of your engine. The cam specs would be very helpful for a chip. Personally, I'd get the proper aluminum heads and cam in it. Those l98 cars are pretty quick. Im aware that that is a bit of work. Bringing it back to stock specs will make it run better and make it easier for diagnostics. The l98 engines were like 245ish hp and the 1990 tbi 350 engines were truck engines w 200-210 hp. They were good engines but not at all performance/fun oriented.

 

No 3rd gen F body came with with the Corvette aluminum heads.
if indeed you have TBI heads you have a restriction due to their casting. At this point you are wanting to replace those heads with some that actually flow now is the time to put either a set of 113 or zz4 GM aluminum heads or go aftermarket and get some 195cc AFR heads

 

AFTERMARKET HEADS get them....

the only good GM head are Vortec heads, and by the time you machine them its wiser to buy new aftermarket heads that will be better in everyway from anything GM made.

 

I'll suggest that those heads aren't going to result in that kind of performance.
"Falling on its face" points to another issue (or more) that's preventing further engine RPM. While the TPI was never for high RPM, those engines would still go to redline when all was well.

Ignition and or fueling might be an issue. A fuel pressure gauge taped to the windshield (on the outside) might show low pressure under those conditions. Ignition is more difficult other than insuring it's been set correctly.

That said, there is one thing that comes to mind that manifests itself just as you describe and that's valve springs.
If they're weak, they very well could be giving up at higher RPM and allowing the valve to float or bounce. When happens it really does fall off a cliff.
Food for thought anyway.

 

Sorry, i mis-spoke, yeah, they were not the vette heads but the l98 heads are different than what you have on there now. More my point was that the ecu/prom isn't proper for that engine. So you will have numerous ignition and fueling issues. To make this ecu/prom happy you'll need the stock stuff. You could also get a custom prom for the engine you have. It falling on its face up high could be the component mismatch or a fuel/timing issue or all of the above.

 

The tune won't be perfect, but the HEADS won't causeAs SkinnyZ rightly pointed out, ^That^ is cause by an actual problem...not the heads.

 

810 heads flow 185 cfm. The stock 083s barely broke 200 cfm. The 113s used in the Corvettes were not much better. The ZZ4s had an improved casting and flowed a bit more. I had 810s on a flat top 350 at 10.2:1 and still made 340 hp with a ZZ4 cam where the ZZ4 was rated 355 hp with 113s. With the tiny factory cam the 810 TBI heads will be even less of a power difference.

Falling on its face at high rpm is one of 4 possibilites. 1.) Weak fuel delivery system starving it for fuel. 2.) Loss of ignition spark output or timing advance control through the EST system. 3.) Weak valve springs allowing valve float. 4.) Restricted exhaust system.

 

Exactly!

 

Exactly!

 

5.) Restrictive intake. OP didn't seem to mention the current intake setup, and it is more likely to be #1 or #2.

 

Ha ha ha. Memory lane. At my last job, we put a Jeep 4.0 INTO A UNIMOG. The parts that I used to connect the Holley carb to the original Unimog air cleaner assy fell together beautifully and I was thrilled to maintain/used the 'Mog Air cleaner assy still.

Thing ran great up to about 3500 RPM, the broke up, ran like **** and fell on it's face. Wouldn't go above about 3800 at all. WTF? I can't remember how I got to checking it, but I disconnected the ducting at the air filter housing's outlet and the thing ran like a raped ape....for a Unimog! Turns out that sucking ~190hp worth of air through an 88hp air filter housing....that don't work.

 

OK, I think there was some confusion about the not liking WOT comment I made.
I do know that the heads are NOT the cause of that. I mentioned that is why I was pulling the intake apart, to do injectors, distributor, and replace all the gaskets. I also found damaged gaskets in the throttle body and broken vacuum lines. Fuel pressure is good, checked with a gauge and all that back when I did the tank and pump. I just never touched the injectors then. I'm sure they had junk in them based on what was in the tank, like i said possible contamination due to vandalism. The distributor internals were all rusty as well with loose debris too. Plugs were good.

I happened to notice the heads while it was apart and started thinking how much performance loss it would cause, maybe 10-25 hp or so? I dunno.
It ran before, and it'll run after with those heads, just not ideal.

As for the cam and whats in the shortblock... yes, I dont what it really is. Therefore by just putting a set of even oem heads may not be the right solution.
What is really needed is to pull the whole motor out and go though it. I dont even know if the chip in the ecm is stock or not.
Intake is the stock MAF TPI setup.
Car is not worth aftermarket heads. They would be more than I paid for the entire car. It is not my only car nor a priority. I'd even consider motor swaps, maybe even an LS swap. I also thought about dropping in a low mileage LT1 I have. Who knows.