Nighthawkf-117

iTrader: (1)

Hey guys,
Deciding between rebuilding my heads or just replacing them. I have a 1991 305 tbi. Is there a source for remanufactured or new heads for this engine? Is there a way to find my casting number without pulling the valve covers? I know if I replace the heads with anything other than what's on there now I'll need a tune.
Thanks
Bill

John in RI

iTrader: (167)

My 2-cents,.........

I'd scrap them and install 305 TPI heads before i spent any money on TBI heads.

sbc lover

more than likely you have the 'beloved' 187 castings with it being a LO3 motor, casting #'s are under the valve covers in between the valves and under one of the middle intake runners will have the last 3#'s also if the intake is off... I don't think you can really tell otherwise. I was just looking at this topic last night on TG.O and it depends what u are looking at as far as heads go, the 305 needs the smaller chambers to keep CR up but also has smaller valves so the flow potential is going to suffer, reports of minor porting and opening up the bowl help a bit, of course the rpm is going to be limited due to the swirl vane. these tbi motors were designed with emissions/mpg/torque in mind and at the time, the technology didn't allow much for 'performance'..

have ya gotten much of the, 'just get a 350' yet?.. I have, I know the feeling of just dumping the motor, I see them as an underdog and they prob always will, though the new injection systems and heads give the 305 more potential than they had before..

sbc lover

Is there any particular reason you are looking for a 'fresh' set of heads? is the motor burning oil? are they going on a worn block?

Nighthawkf-117

iTrader: (1)

The motor is burning oil. But it only has 110k miles so it has plenty of life left. I could probably just refresh the heads but it would be alot easyer to just put new heads on. I know a local shop that will sell me remanufactured assembled 187 heads for only $300. What heads came on the TPI engines? I'm right that assuming any heads other than stock will require a tune to run right?

sbc lover

I have been looking around for a set of rebuilt 187s and most places will charge that with exchange or valve job on yours, so not bad if it is a reputable shop.. you can even get a set of tpi heads for that outright somtimes.. 081 is the TPI head which is a centerbolt version of the 416 H.O. head before 87 for the 305, flow is slightly greater than the TBI heads and you should be able to use those also with no tuning mods with everything else staying the same on your LO3. Keep in mind, as you make mods to that engine, if there is much change in any way, the stock tune will not accommodate it as the injectors will be feeding stock parameters. So, yes, If you put stock TPI 305 heads on a stock TBI 305, it should be able to accommodate the increased flow. Now that's with everything else being stock, change out the cam or put on a free flowing exhaust, the stock tune wont handle much more hp... hope this helps

John in RI

iTrader: (167)

Might as well throw it out there.....


https://www.thirdgen.org/forums/engi...-cylinder.html




I've still got a set of used stock ( not rebuild ) 081 heads I could sell too.

sbc lover

that's the heads there nice pics!!

Fast355

iTrader: (2)

To run ANY OTHER HEAD than the 187 your TBI ECM will need to be recalibrated. Even when it is recalibrated you will lose torque EVERYWHERE under 4,500 rpm compared to the swirl ports.

John in RI

iTrader: (167)

From a thread you might remember:

https://www.thirdgen.org/forums/tbi/...ads-why-2.html

I was faced with the same choice in the past; rebuild swirl ports or use TPI heads. Once completed the swap I never noticed any drop in TQ after making the TPI head swap,........ then again; I swapped to 3.42 gears at the same time.



Other "mods" were a Full TPI exhaust, Smog Delete, and an "HO" air cleaner.




Could the 'tuning' have used a tweak,... probably. I continued to use the stock 91 TBI ECM. It was never recalibrated and I was very satisfied with the cars "performance". Did I loose HP / TQ....... Couldn't tell Ya'. If I did, I never missed it. Please; understand that I'm not arguing that I did or didn't, I am simply trying to explain that the 'need' for programing is often exagerated. EVERY car with a fuel injector will beneift from a proper ECM/PCM 'tune'.

Fast355

iTrader: (2)

I built a flattop piston 305 HO with 081 heads. The engine flat refused to run on the stock tune. It was so lean that I had to swap 350 injectors in it and use the marine regulator aka VAFPR. I also had to advance the timing nearly 10* over stock.

John in RI

iTrader: (167)

What 'tune' were you adjusting ?? Did you really install TBI induction on that 305 HO ?? What harness and ECM/Chip was used ?? Was there a Cam swap of porting involved ?? And to state the OBVIOUS, regardless of why they were installed; the addition of 350 injectors on a 305 engine is going to REQUIRE an ECM tune.


Based on what I just read that example is VERY different that the OP,.... an apples to oranges comparision. You custom built an engine by ( at least ) putting centerbolt heads on a flat tappet motor & converted it to fuel injection. He's talking about an 305 LO3 to TPI head swap - ONLY.

Fast355

iTrader: (2)

Yes I really did replace the Q-Jet with a TBI setup. It was a flat top piston 305 with a tiny 194/203 @ .050" stock cam in it and I replaced the cracked 601 head with a set of rebuilt 081s. When I rebuilt the engine I converted to TBI. Was running a factory 305 ECM from a 91 Caprice. I could not find a 305 truck chip at the time for my 7747 ecm. Harness was from a 92 G20 that I robbed the TBI setup from. I swapped everything, fuel tank, fuel lines, harness, etc. I added the IAT wiring and IAT sensor. With tuning it made 181 rwhp/268 rwtq on a mustang dyno despite breathing through stock intake and exhaust manifolds and single 3" cat, spinning a mechanical fan and running through a 700r4, 2 piece driveshaft, and 8.5" 10-bolt.

Obviously the 350 injectors required tuning, they had to be installed to compensate for a lean condition that caused the engine to buck and surge and even backfire at WOT.

As for the timing the non swirl heads require up to 10° more timing and the additional timing is non linear.