Super_GTA

Afternoon everyone. I've been having a hell of a time with this new motor. Almost everything is new, all sensors, dizzy, afpr, wires, plugs, filters, etc. What I can't seem to figure out is why the motor flatlines at 3500 rpm. I have almost no power above that. Sorry, before I go any further. It's an 89 Pontiac Trans Am GTA. Originally had 305, but I dropped it like a bad habit after a rod knock. Now has a 350. The motor will rev past that, but there's no more power. Now the whole fuel system is from the 305, but I do have an afpr. I've taken the car for a spin with a fuel pressure gauge taped to the windshield, and the fp seems to be fine, doesn't drop off at all. The only things I kept from the original motor are the balancer, fuel system, intake, computer, and esc. Could the 350 knock sensor and the 305 esc be detecting false knock and pulling timing? I hear no knocking, the motor just purrs. Freshly rebuilt by K.P. Engines. The car still has the original cats on there, which I think one may be rattling around a bit inside. If one of those is clogged, will it cause this? Sorry for the long post guys, just trying to cover my bases. I also readjusted the valve to 1/4 past zero lash. The motor was intended for a police interceptor with a carb. I put f/i on top of it, would this be an issue? K.P. Engines also screwed me on the heads. The original heads wouldn't bolt up to my intake, so I sent them back and they sent me some that would work, but they are a 193 casting. I do believe those are the swirl port heads used for the tbi cars, correct me if I'm wrong. Are the heads killing my motor? I have a set of 305 heads from the old motor at my disposal, which are 081 castings. I can't think of anything else at the moment. If I do, I'll let you know. Thanks for your help.

Stekman

What timing cover is on there? More importantly, where is the timing indicator? A 350 (aftermarket) cover places the timing tab at about 1:30. On the balancer, that is also where the indicator lines up. If you used the 305 balancer, the indicator is geared for a tab which normally sits at 12:00.

Point in case: check your timing.

Super_GTA

Timing tab was at 2:00 on old timing cover and sits in same position with the new one. I checked the timing and it sits right where it should at 6* BTDC.

RWB____s

You said that one of your cats is rattling around. That is probably the problem. The inside of the cat is broken loose and blocking the exhaust. change the cat and I'll bet it will be much better.
I have had this happen to me also and had the same type of performance problems.

iggy1991

Whats the PSI of the fuel around the time it looses power.

DuronClocker

iTrader: (1)

The injectors could be the issue. The 350s came with 22# vs. the 305s 19#. Since the EPROM is designed for the 19#, it will know how to correct properly, but it may not be able to past a certain point.

Is the car even a TPI motor, or is it a TBI motor? Since you're saying its the stock intake off an '89 GTA, I'm going to assume it is TPI, though I could be wrong.

Could be a horrible horrible mismatch of parts too. Does it rev to 4500-5000, but just have no power over 3500rpm, or does it just not rev past 3500rpm? Does it feel very stron under 3500rpm though? Maybe they put a nice little RV cam in there.

Those 081 head castings are very good heads compared to the TBI swirl ports. In fact, with a little bit of work those 081 castings can turn out to give very nice performance for the cost. Port them yourself (takes a looong time, but worth it), and then get them re-cut for 1.94/1.6 intake/exhaust valves, and they will outflow a stock L98 head by quite a bit.

RB83L69

If you put yerbasic rebuilder's motor in there, you probably ended up with about 8¼:1 compression, truck TBI heads, and a 929 cam. Any of which by itself would account for it running lazy. All 3 together would seal its fate.

Check the obvious external things, like fuel delivery and exhaust; but don't expect much out of some motor that carries buzzwords like "police interceptor", whatever that is supposed to mean. That's sucker bait. Sound to me like you might have traded downwards when you swapped that motor in there.

Super_GTA

Thanks for the quick replies I think I got screwed on this motor. I am in the process of porting the 081 heads, but like you said, it takes a while. How do I figure our the compression ratio based on a compression tester reading? Is there a conversion chart or formula out there?

RB83L69

No. Not possible.

Too many variables.

The cam profile in particular can cause HUGE variations in compression tester readings. Even the intake centerline (timing set installation) will cause variation.

VetNutJim

You're REAL screwed on the 193 Heads.
The swirl post is a MAJOR restriction to flow.

If you DO get it to run past 3500 it'll stop again at 4500 due to the heads.

Those are truck heads designed for HEAVY trucks.
They will make GREAT torque to about 4500 RPM and then they will act like a govenor.....

They are DIRT cheap.
Those engine building places buy them and pawn them off on the unsuspecting public.

They're best used to add to your local landfill.