I need to ask those more knowledgeable what else can I do to make power with the current configuration?

6 months ago I thought I had a few repairs to get my 89 back on the road, naturally that wasn’t the case. In the end I decided not to pull the engine at this point to build a 383 in fear of it being laid up for another year (or more) but to put it back together & plan a future build.

So here’s what I’ve done thus far, but am I missing something major or are there little things I can add to what I’ve done that will make more power? Cam is a TPIS super L98 (220/220 duration, .427/.427 lift with 112 lsa) & while replacing valve seals I changed the springs that match the cam. I ended up adding 1.6 full roller rockers in fear of the cam being a little too small. Doing the math I figured lift would be .456/.456 but does this effect duration too? Since I am keeping the stock TPI intake I did hand porting of the plenum, runners & intake, nothing dramatic but clean up, smooth & port match. I also port matched the entrance to the heads but only an inch or so to open up the pinch point at the pushrods. I’ve been reassembling, valve covers are on but intake still off.

I've thought about changing the radiator but it’s supposed to have the heavy duty radiator & I can’t figure out the correct replacement. I was still planning on using the stock TPI replacement gaskets but noticed I may need to trim them at the base as they don’t match the port very well & would add a little blockage. Looks like the casting is off a bit from the beginning. I was thinking of doing the coolant bypass of the throttle body, a lower thermostat & having the chip programmed for lower fan kick on temps. I’m not sure moving the intake temp sensor upstream is of any benefit but am considering it since it’s so easily accessed. I have also wondered if the MAF screen removal is worth doing? I haven’t removed the pollution equipment but was thinking of doing that as well just to clean things up under the hood, if for no other reason. Thoughts? Am I missing something(s)?

 

You don't mention anything about the exhaust? Is there a reason you're avoiding that? Increasing rocker ratio does add a small amount of duration. How much depends on the ramps but it's probably around 2 deg increase. The length and diameter of the intake are a restriction. Shortening the intake (runners) or enlarging their diameter will provide more power. If you ported the base well, I'd suggested bigger runners (ASM/TPIS), Superram upper, or DIY SuperRam via megaported SLPs.

Since you were "brave enough" to port your heads, I'll assume you did a good job on your intake base. In short, better runners and better exhaust. FWIW, if you're not willing to buy more parts, porting the exhaust manifolds (inlets) can be an improvement.

 

Not avoiding just skipped it. The 89 has stock exhaust manifolds & exhaust although I did add a flowmaster cat back exhaust well over a decade ago. I don’t know if or what I’d want to do with the exhaust, so I guess it just slipped my mind.

 

The TB coolant bypass was one for the first mods to my 'new' '89 three yrs ago.

A 160 deg t-stat will add some ponies for sure.

Don't forget to toss that damn "frisbee" from front of the WP pulley.

Opening up the air filter housing intake couldn't hurt either.

 

Hello Sir,

I would do the screens out and a little porting on the Mass-Air, also a cheap power increase can be had by installing an Adjustable Fuel Regulator.
I have left all my pollution stuff on mine as all the computer's tables are based on these reading and temps and keeps your car running smooth and fuel efficient. Further, if you live in colder climates and like a good idle quality, I would leave it alone. Yes get rid of the frisbee and relocate the the temp sensor. I would upgrade your coil and module with a Davis unit, buy the best plugs and wires you can and cut the air lid and add a K&N air filter. Also, i notice different plugs gives your car a different feel some of the expensive plugs were worse than plain old A.C. Delco's. My two cents you will be happy with the power increase you should be looking at about 50+ HP.

Good Luck. - Jarrod

 

This is like reading a thread from 1995! Wow.



I agree with Greggpenn about exhaust. Headers and dual exhaust. That would give you a significant increase at this point. Well over 20 hp beyond the changes that you've already made.

 

Cam choice is fine, but I'd have probably chosen my cam after I decided things about the intake. Good 1.6RR is a given.

If you do a 383, must do exhaust. Should look around for TPiS 1.75" headers, and skip their Y pipe and just do true duals. 2.5" is fine, and then you pick the mufflers you want, they'll all make about the same power. Its the sound that changes, and thats what you have to live with.

As far as the intake, you have to choose where you want the power band to be, and that kinda forces you one way or the other. Finding the aftermarket TPI-style parts is hard now, most of the selection we had 10 years ago is gone. So you're left with ebay and looking for things there, or heavy heavy porting. If you like the stock band, then you can just port the hell out of everything and try to find a new base manifold. The stock base manifold doesn't have enough to port out as I recall.

If you want to move the band up in RPM, then you're looking at shortening the runner length, and then you have to find a SuperRam used to make it a more fun midrange car, or if you want a high rpm screamer (and have built the 383 for it) then TPiS Miniram. Kinda like an LT1 conversion in terms of powerband, and pushes you to things like a higher RPM TC (if auto) or more rear gearing.

Then the chip comes last, after you've done all the intake changes, because anything close to stock programming will have dead spots in your powerband with these two intakes, it won't have enough timing and or fuel in places. You will probably need larger injectors for the 383 either way.

As far as the freebee mods, those are fine, the lower stat temp allows you to run a little more timing provided you can keep it that cool. The frisbee of course needs to go either way. Do not move the intake temp sensor. The headers you choose will push you to how you want to deal with AIR and EGR, I yanked em all off. The radiator I run is a DeWitt and I'm very happy with it.