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Looking At a C4 Have Questions on the Build

Old 09-30-2018, 01:40 PM
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TheAllusionist
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Default Looking At a C4 Have Questions on the Build

I am sure this type of post happens all the time and I apologize, I have been doing searches trying to find answers and this may be a bit unique. I am doing a stealth build on a Black 1986 Porsche 944 Turbo with 48,000 original miles and the Corvette of that error was sort of the "Arch-Nemesis" of my car. Recently a black 1986 Corvette has come up for sale and it would seem fun to have the two cars in same color. It seems that the owner has done all the right things on this car, but I wanted to ask the experts about the build and what else they would do to it if it was there to see the full potential of this car (believe me the Porsche is going to be a monster in stock clothing, I would like to give Corvette what it needs to see it's potential as well). So I have been trying to talk myself out of buying this car for a couple weeks and it keeps calling my name and would be something that figure would be pretty bullet proof and I could drive daily during good weather, Here are the upgrades:

Hi performance professionally built (It's has a custom ground isky cam. 510 lift 512 duration) original L98 350 cu inch engine with low miles.
Aluminum AFR heads, roller cam/lifters/rocker arms.
1100 cfm aftermarket throttle body.
MSD 6AL ignition.
Long tube ceramic coated headers.
Rebuilt 4+3 transmission. Modified overdrive switch makes shifting in and out of overdrive 100% manual. Works in any gear.
Magnaflow catback exhaust system.
Performance Bilstein shocks.
Frame reinforcements with a strut brace.
C5 wheels with continental extreme contact tires. 90% tread.
Baer ventilated front brakes. Huge improvement over stock brakes.

The owner tracks it a couple days a year and it comes with another set of wheels with track tires.

So it looks like major items have been addressed and he is asking $5,000.00 and I know how you never get what you put into this kind of car what you put into it and it looks like a good way to get into Corvette ownership. My first car which I have had for 38 years is a 1947 Chevy Fleetmaster coupe, by original love is small block Chevy, American made so this is a tough one to pass up, looking for advice from those who know a lot more than I do.

Thanks in advance for your time.
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Old 09-30-2018, 02:08 PM
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its worth 5000.00 with all he done to it, wish we had some photos of car

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Old 09-30-2018, 02:24 PM
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Originally Posted by fparkin View Post
its worth 5000.00 with all he done to it, wish we had some photos of car
It is a bit of a drive so I haven't gone and looked at it personally, may do that next weekend, but from the pictures it looks pretty good, obviously not concourse and the inside plastic looks slightly rough, but has new carpet and seat covers and until I looked at prices of C4s thought it fell into the category of "If it looks to good to be true...." but I have been corresponding a bit with the owner for a few weeks and it sounds like people want a brand new looking car and don't appreciate what he has done to it and he would never get out of it what he would have to put into a paint job.

I am looking for something I can drive and take to a grocery store and not be terrified that some small chip or ding happens, I take great care of my stuff, but driving over the pass rocks and gravel hit your car at times, I would like something bullet proof and not concourse, with performance being the emphasis and this seems like a good starting point.



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Old 09-30-2018, 02:32 PM
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still looks good plastic little rough I paid 5500.00 for a 84 corvette auto 70k it was little rough but every thing worked
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Old 09-30-2018, 02:37 PM
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Yes, I am OK with it and a detail and cool floor mats etc.would help, I just don't want to get it if it was a slug, if you are driving a vette you want it to be able to handle itself, I know it won't take on a newer high performance car, but I don't want a run of the mill car embarrassing me, That is the reason I am doing a stealth build on my 951, newer tuners are quick and I want to hold my own, so 400+ RWHP should do the trick and stock look help maintain value even if I never sell it. I actually have my very first car, a 1947 Chevy Fleetmaster coupe, I tend to keep cars a long time.
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Old 09-30-2018, 02:50 PM
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There are a lot of C4s for sale here in the Pacific Northwest but this seems like a good buy for what is in the engine. If it runs as well as the owner states you will be happy with it. You may be looking at replacing rubber suspension components if they have not been replaced. I am not sure how much more you are expecting for performance gains but it seems like it is close to being maxed out without spending a whole lot more money.
I keep an eye on Corvette pricing here in the NW and this seems like one of the better buys. If you offer less and get it even better, but it seems priced about right. Check for frame rust depending on past driving location for the car.
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Old 09-30-2018, 03:36 PM
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Originally Posted by Fiberbundle View Post
There are a lot of C4s for sale here in the Pacific Northwest but this seems like a good buy for what is in the engine. If it runs as well as the owner states you will be happy with it. You may be looking at replacing rubber suspension components if they have not been replaced. I am not sure how much more you are expecting for performance gains but it seems like it is close to being maxed out without spending a whole lot more money.
I keep an eye on Corvette pricing here in the NW and this seems like one of the better buys. If you offer less and get it even better, but it seems priced about right. Check for frame rust depending on past driving location for the car.
Thanks for the info, they had been asking more and have come down, and I have been keeping an eye on pricing and it seems that they go from 3,750 to 9,000 obviously depending on the car, this just seemed like most of what you would want done had been.

My real question is how much RWHP are we potentially looking at with these mods, 300, 325 or more? or is that wishful thinking? I know the L98 put out torque real fast and that is what wins races stoplight to stoplight, not that I am looking to race it on the street, but that is just to explain I am talking about short sprints it should do well.
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Old 09-30-2018, 03:56 PM
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I do not think 300 rhhp is there with the TPI intake system. TPI is the limiting component. Better ability to increase air fuel intake and maybe 300 RHWP is there for you. AFR heads, cam and exhaust are there for the ability to breathe better if the intake is improved.
Also rechecked the ad and it says or best offer so $4000 and you have the money for a better intake system.
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Old 09-30-2018, 06:06 PM
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It is best offer and he has already brought it down, I am not the type to beat someone up on something like this. But I may toss out $4,800 but he has a lot of money in this car.

What is the hot intake for the L98 engine? Unless the stock motor has steel internals I doubt I will supercharge it or run nitrous. So what is the next best option? Does a later intake system bolt on?
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Old 10-01-2018, 01:36 AM
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I know there are a number of options that are around but I am not the one to ask for specifics. I have seen something by I think a corporation called First TPI on one at a show that was definitely a well built early C4. I have also seen some changed drastically but some of those options required hood modifications.
I am sure there are TPI experts on the forum who will chime in especially if you post a request looking specifically for options on changing out the TPI setup.
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Old 10-01-2018, 09:45 AM
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Originally Posted by Fiberbundle View Post
I know there are a number of options that are around but I am not the one to ask for specifics. I have seen something by I think a corporation called First TPI on one at a show that was definitely a well built early C4. I have also seen some changed drastically but some of those options required hood modifications.
I am sure there are TPI experts on the forum who will chime in especially if you post a request looking specifically for options on changing out the TPI setup.
I agree with the general direction Fiberbundle is taking you. The problem with the TPI intake isn't the diameter of the runner tubes, but rather their length. They set up a resonance that boosts intake performance around 3000rpm but hurts it above 4500rpm or so. fatter runners can shift that around a bit, but they can't escape it. The only solution is an intake with shorter runners. The hot intake seems to be a Holley Stealth Ram, but it doesn't fit under a stock hood. The short-runner Mini Ram is much like an LT1/4 intake, and is a good "easy button" solution. It will allow your engine to realize the potential of those heads and cam. Those aren't the only two solutions - basically you want something with much shorter runners than the TPI has.

I don't think it's impossible to get 300rwhp with the TPI-based intake that's on there now, depending on exactly what heads and cam are in there (the cam specs you quoted don't quite add up - what's the true duration and what is the lobe separation angle). It's just that so much more is available with a better intake.
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Old 10-01-2018, 10:20 AM
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Originally Posted by MatthewMiller View Post
I agree with the general direction Fiberbundle is taking you. The problem with the TPI intake isn't the diameter of the runner tubes, but rather their length. They set up a resonance that boosts intake performance around 3000rpm but hurts it above 4500rpm or so. fatter runners can shift that around a bit, but they can't escape it. The only solution is an intake with shorter runners. The hot intake seems to be a Holley Stealth Ram, but it doesn't fit under a stock hood. The short-runner Mini Ram is much like an LT1/4 intake, and is a good "easy button" solution. It will allow your engine to realize the potential of those heads and cam. Those aren't the only two solutions - basically you want something with much shorter runners than the TPI has.

I don't think it's impossible to get 300rwhp with the TPI-based intake that's on there now, depending on exactly what heads and cam are in there (the cam specs you quoted don't quite add up - what's the true duration and what is the lobe separation angle). It's just that so much more is available with a better intake.
Matthew, thanks. I realize this engine is designed for fast torque an nd not top end max HP, not that is a bad thing and maybe I should look at increasing HP and torque equally in proportion as it is. In general want to make sure intake is a Big weak point that can easily brought up to the rest of the cars performance parts and not leave unclaimed power on the table.

With all that said if there is a shorter runner length intake system that fits under the stock hood, I would consider it, just trying to avoid the slippery slope I already went down on the 951, need a predetermined game plan of limited scope where I stop and just enjoy the car! Lol
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Old 10-01-2018, 10:27 AM
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Originally Posted by MatthewMiller View Post
I agree with the general direction Fiberbundle is taking you. The problem with the TPI intake isn't the diameter of the runner tubes, but rather their length. They set up a resonance that boosts intake performance around 3000rpm but hurts it above 4500rpm or so. fatter runners can shift that around a bit, but they can't escape it. The only solution is an intake with shorter runners. The hot intake seems to be a Holley Stealth Ram, but it doesn't fit under a stock hood. The short-runner Mini Ram is much like an LT1/4 intake, and is a good "easy button" solution. It will allow your engine to realize the potential of those heads and cam. Those aren't the only two solutions - basically you want something with much shorter runners than the TPI has.

I don't think it's impossible to get 300rwhp with the TPI-based intake that's on there now, depending on exactly what heads and cam are in there (the cam specs you quoted don't quite add up - what's the true duration and what is the lobe separation angle). It's just that so much more is available with a better intake.
P.S. the mini ram you mention and the FIRST intake are what my research late last night turned up so that may be the simplist answer. On the older Porsches A MAF and modern fuel and air regulation systems are supposed to make a world of difference not certain if there is a lot to be gained in the corvette, this car had chip burnt for this build so if I change much I may need to pay for new chips as it is.
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Old 10-01-2018, 10:44 AM
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Originally Posted by TheAllusionist View Post
Matthew, thanks. I realize this engine is designed for fast torque an nd not top end max HP, not that is a bad thing and maybe I should look at increasing HP and torque equally in proportion as it is. In general want to make sure intake is a Big weak point that can easily brought up to the rest of the cars performance parts and not leave unclaimed power on the table.
There is a lot of myth and misinfo out there about the TPI intake. It doesn't increase torque off idle or up to roughly 2000rpm. It only provides a torque spike around 3000rpm (maybe a bit lower for a stock one). In return for that torque spike, the torque and therefore power both fall off a cliff at 5000rpm. OTOH, with decent heads and some kind of aftermarket cam, that engine is set up to increase power mostly in the top half of its rpm range (guessing 4000-6000rpm) - right where the TPI intake is hobbling it. A short-runner intake will not hurt off-idle grunt. It will lose the TPI torque spike, but it will extend your useful powerband quite a bit. The end result is a much more linear torque curve and a much more flexible engine with a much wider useful power band.

The FIRST TPI intake is considered the best flowing long-runner intake, I believe. But it's still a long-runner intake with the disadvantages that entails. I can't imagine spending the money for that, only to still have a Helmholtz resonator effect shutting down the intake flow in the higher ranges of your power band. I doubt you'd need a new chip burned for a short-runner intake. You might benefit from having one burned that added a little more timing advance where the TPI torque spike occurs in the rpm range right now. That's because there will be reduced cylinder pressure in that range with the short-runner intake, and therefore more ability to safely tolerate more timing advance.
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Old 10-01-2018, 03:21 PM
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Matthew,
Thanks, I was trying to get good information as I have researched and read a lot about the great torque design of the TPI and thought maybe I was letting HP leed me to not appreciating the Torque.

But looking at the pictures, I see that it appears to have an Eddlebrock intake manifold and runners of some sort (Edelbrock High-Flo TPI intake runner system)? So perhaps I just drive it for now if I get it.

Thanks everyone for sharing your knowledge and time with me.

Russell

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Old 10-01-2018, 06:01 PM
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Originally Posted by TheAllusionist View Post
Matthew,
Thanks, I was trying to get good information as I have researched and read a lot about the great torque design of the TPI and thought maybe I was letting HP leed me to not appreciating the Torque.

But looking at the pictures, I see that it appears to have an Eddlebrock intake manifold and runners of some sort (Edelbrock High-Flo TPI intake runner system)? So perhaps I just drive it for now if I get it.
Don't get caught up in the torque-trumps-power BS. Torque at the crankshaft means nothing. The number tells you how fast your car will accelerate at any given speed is the power it can produce at that speed, period. All the talk about torque is mostly people who want to make this more complicated than it is. The ideal torque curve is the one that is as flat and wide as possible. That will make for an engine that has a wide useful range of rpm and is very flexible. The magnitude of that curve doesn't matter a single bit. The fact is that a TPI engine has a peakier and shorter torque curve than any short-runner engine (such as an LT1/4). It was made for a very specific purpose that no longer existed when the 1980s came to a close. It is less flexible with a narrower powerband than all shorter-runner engines that have come since.

Those Edelbrock runners are still long TPI-style runners, so they'll still cause the dropoff of power/torque. However, it's always legitimate to just drive for a while while deciding what to do, if anything.
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Old 10-02-2018, 07:13 AM
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Drive it just like it is for awhile, go from there. Everyone focuses on a rwhp# thats not everything
Stoplight to stoplight torques more fun;the TPI has a ton of airspeed so i has good throttle response and "feels faster"..for a minute.

I have one of those "rpm/hp"motors and its not all that great in slower traffic not to mention rpm is expensive and parts are shortlived.
On a tight autocross course it would suck.
If you get bored then do a 400 with a converted LT1 intake or a used miniram.TPIS is a little too proud of them.

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Old 10-02-2018, 03:53 PM
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Thanks everyone for sharing your insite!
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Old 10-02-2018, 06:39 PM
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Originally Posted by cuisinartvette View Post
Drive it just like it is for awhile, go from there. Everyone focuses on a rwhp# thats not everything
Stoplight to stoplight torques more fun.
I would agree that peak rwhp isn't everything - not by a long shot. However, average and accessible rwhp most definitely is everything. That is by definition of the term "power." On the torque side, torque numbers (as in "how much torque does it make?") don't mean a single thing at all - nothing - unless you're trying to spec a transmission to withstand a certain torque input. However, as noted the shape of the torque curve is very important and goes hand in hand with making good average and accessible power.

In a way, this sounds like I'm just being pedantic. But it's very important to understanding why a TPI intake (with higher peak torque numbers) is a bad idea, whereas a short-runner intake (with broad torque curve and more flexible powerband) is the better answer.
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Old 10-02-2018, 07:20 PM
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Look - Just my $0.02 - but a well set up C4 is a VERY good handling car. If the car has 13" brakes - sometimes called the J55 brakes, it'll do pretty darn well stopping.

As far as tranny goes - the 4+3 is about the worst of the C4 Vette options - it was not one of GM's better ideas - but its workable...

Now - lets talk motor. The L98 was not a high power motor - but it makes torque, and I personally want low end torque AND a broad torque band in a street motor. Yes, HP wins all day on the track - where very talented drivers shift frequently to keep the engine "on the cam" at all times. People just don't drive like that on the street. If you buy the car - drive it just like it is for a while and see what you think... If you want - you COULD swap the TPI for a carb set-up and there are intakes that should fit everything under the stock hood - but an aftermarket air cleaner will probably be needed. Yes - the carb will cost you mileage, and will give you some drivability issues - but they do work. If you have doubts ask ANY engine builder that has an in house dyno - he'll tell you a properly tuned carb will make comparable HP to a EFI car.

I will make one other suggestion - try to find a 92 - 96 C4 with the LT1 / LT4 motor and a ZF 6 speed and take it for a ride. The beauty of the LT1 is that it makes 300 HP stock, and it makes 300 ft lb of torque from under 2,000 RPM to 5,750 RPM. It's a very nice street motor. The ZF six speed is a much much better gearbox than the Nash 4 + 3.
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