Good evening to all: First time on the forum. Just got a 1986 C4 that just fell into my lap for almost nothing. Not what I would have chased for but here it is. Looking for performance upgrades and, no, not on a budget. I don't want to rip the car apart but wanted to get some really good advice on how to get this done. Thanks in advance

 

Don't these cars come with something like 2.73 rear gears or something like that?

In which case put in 3.42 or 3.73. One of the biggest bangs for the buck you can get.

 

Depends on what your goals are for the car. If it has the Z51 package it has 3:07 rear gears. Best seat of the pants upgrade in my opinion is long tube headers

 

I think it's the base model. I will double check. I will check into the headers. Would like to see something under the hood with close to 400HP. Just not finding any easy way to get there. Thanks!

 

Welcome to the forum KBAZ, any more details on the 1986? Is it an early model or late model? Auto or Manual? What's the intended use, just a street rod or something more?

 

Not sure if it's early or late. Auto, base model. Street rod (mild). Nothing too crazy

BTW: I like the KBAZ. Pilot stuff is always good.

 

I'll provide mythoughts about this.

Some of the 1986 models had iron heads, mostly the earlier ones, althought a friend has a 1986 that came off the production line a week after mine did, his was iron heads and mine was aluminum heads. His was an automatic and FE1 RPO code for suspension, mine was a manual with Z51 RPO code for suspension, so I suspect that the aluminum heads were prioritized for the higher performance models, but not sure. Most of the 1986 models also had a flat tappet hydraulic lifter/block/cam.

So the extent of the modifications may be long, and note also that TPIS made a 400HP kit way back in the day (today perhaps not).

Problem with 400HP out of a 250HP engine is that many of the components are limiting you... intake, heads, exhaust, lifters, cam shaft, valve springs, rockers, ECM, injectors. Another problem is typical with HP goals, you can achieve 400HP with the L98 changing the aforementioned components with the 400hp goal in mind, but it will be gutless below 4000rpm. I have a neighbor who built his engine for 400HP (probably 350RWHP range more accurately), and it ran great at 5,000-6,000 rpm. My stock L98 felt much better below 5,000 rpm with much better drivability.

So with that in mind... One option for a fun 400hp street performer may be a 383 kit with upgraded roller retrofit valvetrain and AFR195 heads, Super Ram intake, and cam in the 215-225 duration @050 zone, headers/exhaust. If you don't mind giving up torque provided by that combo (which was added by going from 350 to 383 to compensate for the midrange lost) you can go with a MiniRam intake and 220-230 duration @050. I had the former but on a 350 not on a 383, and it was probably a little shy of 400fwhp but felt great. To get that same engine to 400 I would have needed to change the cam and intake, and at 350cu in it would have been more of a dyno queen.

Another popular option is an LS swap, but since a stock LS1 is far short of the goal, it just provides the heads/intake/ecm part of the above equation.

Or you can add a 200 shot of Nitrous?

 

If it's an auto, it has the Dana 36 rear end. The ratio would likely be 2.73, but 3.07 gears were optional (RPO code G44). I always hear 400hp is about as much as you can get away with for a Dana 36, so as long as you're not drag racing it should be okay; but if you want a shorter ratio than 3.07, you will need to upgrade to the Dana 44.

And if you're not looking to tear the car apart, it's possible that an LS swap would actually be the easier way to get to 400, and you might end up with a more drivable car too.

 

L98 typically does not need gearing changes, not until you put an intake on the engine that will let it get some RPM. You need not worry about the D36 with 400hp, its the TQ value combined with the tires that break things, and you can worry about any of that later.

An automatic already has a 2000rpm TC stock, so you need not do anything to it.

You need to build a plan for what you want the car to be like, do you want it to pull 7K RPM? Do you want a cruiser with some more torque? The answer will point to the intake changes you will have to make, and that will drive the cam and head choices. So thats really the primary question here. The custom tune will be after all that is done, and talk to your tuner about the injector size. Working the diff comes after these choices are made.

Right now you can go ahead and get 1 3/4" headers, they need to be stainless or ceramic coated for the heat issues. Replace the cat with a new one or put in true duals otherwise, and pick a muffler based on sound preference alone. You may want to get a heated O2 sensor.

 

long intake runners on TPI are all about high torque, not big HP. Any build requires better flowing heads, better flow intake manifold, free flowing exhaust, camshaft and a tune. no magic bullet.

 

Where is everyone getting the headers and intake components such as runner and base from??

 

Headers: American Racing headers are the best, comes with a matching/fitting X pipe. Summit is one source, or directly from ARH. For a budget header, which is really not budget if you really add up the work involved, is the Hedman premium headers. Not budget as they quickly rust inside an need customization for fitment at the collector, they don't fit up very easily to the stock exhaust, they have a lot of welding spatter and buildup at the exhaust port, so if you clean that up it also may need re-coating. I had a set a while ago, mated to the TPIS Y-Pipe that went through stock exhaust from the Y back. Just get ARH, it's stainless, fits awesome, performs much better if engine is modified. If you need other options, TPIS headers don't seem to be available anymore, but Exotic Muscle sells a Jet Hot Coated steel set that's decent. Camaro headers or Generic SBC headers will not even be close, so don't try that.

Intakes and base: there are at least two people here in the classifieds that sell a lot of intakes, some perhaps sourced from junk yards or personal contacts, or they have a storage full they've collected, who knows. Arizona Speed and Marine still sell the larger/smoother runners, and it fits the Edelbrock/Accell/TPIS/ASM base they are all the same. The lingenfelter Super Ram is my favorite, used a TPIS big mouth base, I sold it last year for a new combo. It was nice, runners ported to 41mm, and plenum cleaned up, thermal barrier coated, helicoils installed, I think I sold it for maybe $1200. Then there's e-bay. Holley also just came out with a high ram but I'm not sure it fits, certainly would need a different throttle body arrangement. Some also need specific fuel rails and regulator.

 

This is very good info. I will save this when I get to the point of (more than likely) building or buying another engine. Thanks!

 

Mine has the iron heads. Looks like ti is definitely the base model.

 

Did you have trouble with tuning it? I understand this can be a problem on that TPI. I am assuming changing heads would also call for intake, etc. I am not finding anything on the fuel injection, etc.

 

That's coming more into focus right now. I am willing to spend the $$$ on it but don't want to get too stupid. I am hearing the tuning can be limited. Trying to find some stand alone fuel injection? Something that does not interfere with the current digital (LCD) gauges, etc. I am hearing that removing any of that will remove the function of all the dashboard. Not sure how much of that is true.

 

Tuning it is only more difficult because there are few people who do tunes anymore, or advertise so, for the Gen 1. Several here can tune it, and I have the software and hardware myself to tune my own if need be, but mine was tuned on a dynojet by the tuner who helped install the engine. Tuning it yourself is not difficult but you need to spend the time learning and tweaking slowly so you don't **** something up. An aftermarket EFI like a Holley or whatever can mess with the dash functions and that has to be figured out for each brand.

 

I have a Holley HP aftermarket ECU, went through the tier 1-3 Holley courses in Bowling Green at the CM. If you go that direction (Holley Terminator, HP, Dominator), recommend taking the tier one class as it covers a lot of wiring, installation, basic setup and basic tuning... and they give you some great deals if you buy the parts/harnesses/tools directly from the school.

Dash works perfect on the 1986. The fuel flow based functions no longer work properly once you upgrade injectors (fuel flow is based on injector pulse width inside the stock computer) and the aftermarket ECU doesn't have that function, but otherwise you have everything on the dash.

If you're not going through that trouble of the aftermarket ECU with the nice advanced tuning features, contact Brian (tunedport90 here on the forum) and he can set you up with changing the EEPROM and tuning, can even help tune, and may have some upgraded components also especially with intakes.

 

could try contacting. DynamicEFI. not sure if programable ecm are still available. founder past away.

 

Thanks for the info. Very helpful. I wasn’t thinking about the pre owned market at all.