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Long tube headers or better intake manifold???

R

rel3rd

Guest
Long tube headers/high flow Cat or Ported Plenum/big runners/better lower intake setup?

If you could only do ONE of those two mods, right now, to your L98 engined 85 Coupe...which one would see the most all around power increase?

Other than a few minor mods, engine is stock. (my mods: K&N, open lid, de-screened maf meter, airfoil, muffler eliminators, high flow catalytic converter) and an adjustable fuel pressure regulator is on the way.
 

Rowdy1

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Headers

No matter what mod you make, it has to be able to let the intake out. Headers will make a small difference alone but with everything else you add, they will be needed later. My $.02;)
 
R

rel3rd

Guest
Thanks for the reply. I already have a ported upper plenum, but didn't get any runners yet. The dilemma is I found a set of LT's and Y pipe for a decent price, so I don't know whether to wait on the intake, or the headers, lol...with a son fresh into college, the funny money is not what it once was... :(
 
Joined
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I would do headers first, since the exhaust systems on our cars are extremely restrictive. I think 85's didn't have pre cats? I am not sure but if they do I would definetly recomend headers, that will you give you more HP with the porting work you've got done.
 
M

Midnight 85

Guest
Thanks for the reply. I already have a ported upper plenum, but didn't get any runners yet. The dilemma is I found a set of LT's and Y pipe for a decent price, so I don't know whether to wait on the intake, or the headers, lol...with a son fresh into college, the funny money is not what it once was... :(

Since the price on the lt's is right I would get them then put them away until you get the intake and do it all. It's the only right way. If you do the intake the poor exhaust is not going to let it breathe. If you put the headers on right away you "might" lean the engine out causing damage. Get all the parts together and do it right.
 
Joined
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Messages
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Since the price on the lt's is right I would get them then put them away until you get the intake and do it all. It's the only right way. If you do the intake the poor exhaust is not going to let it breathe. If you put the headers on right away you "might" lean the engine out causing damage. Get all the parts together and do it right.


How could you lean the engine out by making it breathe better? I have been running TPIS long tube headers for over a year, and have scanned my car several times and I haven't had a lean condition.
 
M

Midnight 85

Guest
You're making me go where I shouldn't go, years ago I could have given you an intelligent answer but that was before computer controlled cars. Back then you would just up the jet size in the carb. What I can tell you is from my experience with my 85 L98. I had installed a VERY mild cam 3 years ago and had a Hypertech chip in the car that was there when I got the car. It ran fine until this past winter, I upgraded to aluminum heads, long tubes and a true dual exhaust. I also mildly ported the heads, intake and plenum. When I fired the car up to set timing etc. I glanced down and my brand new headers were glowing red. I spent the next 3 weeks chasing what I thought to be a vacuum leak to no avail, nothing was amiss there. I finally talked to Jesse Azzato, (Azzatochips.com) he went to great lengths to help me but in the end we both agreed I needed a different fuel curve, I was running lean, even at only 1,500 rpm. Jesse burnt me a new chip and the problem was solved, plus the car ran like never before. So, I'm not smart enough to give you actual particulars as to what leans them out when you make it breathe better except for what I said about needing more fuel. Maybe someone else here can do that that understands computer-ese. I just answered your post because I didn't want to hear of you ruining an engine. I hope this helps you understand.
 
R

rel3rd

Guest
How could you lean the engine out by making it breathe better? I have been running TPIS long tube headers for over a year, and have scanned my car several times and I haven't had a lean condition.

Vettefan87, I'm with Midnight 85 on this one, if for no other reason aside from me experiencing this exact problem on another vehicle.

All of my previous Chevy vehicles were carberated (and usually nitroused, lol), so I haven't played around with an "electronic" GM vehicle...ever, but for the last 10 or so years I have been playing around with several supercharged and nitroused Fords, both my own and others that I have tuned. I had a 94 5.0 Mustang that was somewhat of a hybrid (or bastard) as far as ecm's was concerned. It wasn't quite an OBDI, but yet it wasn't quite an OBDII either. Anyway, the car ran very well, but always felt like it flattened out at 4500 rpm's or so. When I added better exhaust (headers, off road X pipe, straight thru mufflers), conical K&N w/aftermarket piping, and underdriven pullies to free up some rotational mass, the car ran GREAT at lower rpm's, but still seemed to go flat up above 4500 rpm's.

I finally had all but given up on the car, and decided to try something simple, on a whim. The item was an adjustable fuel pressure regulator. The "stock" base pressure was 38psi, and I set it at 45psi just to test my theory. Car immediately revved cleanly to 5800rpm's or so, even with it's stock restrictive intake manifold and wheezy cylinder heads. At "normal" driving times, car was unchanged since the ecm adapted itself, as it should, to the amount of air being ingested. On the Fords, it turned out that at WOT, the ecm doesn't control fuel in nearly the same way it does at cruise, and idle. It has set parameters, but when the "mechanical" setting (i.e., fuel pressure) is changed, there's no way for it to over-ride that with the factory ecm. You'd have to have some sort of aftermarket tuning via a chip, or piggyback tuner of some sort.

I have no idea if our Corvette's work in the same fashion, but if they do, then Midnight 85 is correct in thinking that I will get a lean condition. It shouldn't change at "normal" driving rpm's, but at WOT there will be a lean condition. Like I said...this is IF the Corvette ecm works in the same way. I'm going to believe that it does, until someone proves it different, since my 85 acts the same exact way my old 94 Mustang did when I made it breathe a little better. It runs great at cruise and part throttle, but seems to "level off", or "flatten" at wot. I know the stock intakes seem to be an issue, but if you're making the engine breathe better, it absolutely needs more fuel to make anymore power.

A crude and exaggerated comparison would be a nitroused or supercharged engine. You spray a 200hp shot of nitrous or pump 15# of boost into your engine and don't add anymore fuel, you lean out severely, usually break or hurt parts and make no power. Add the proper fuel to either equation and the car screams...That's why generic chips like Hypertech usually don't work. No way possible to tell how efficient engine "A" is, as compared to engine "B"...

Take my stock motored 85, have the best tuner in the world burn a chip for it, then let me add a nice ported set of heads, long tubes, open exhaust, custom cold air intake setup, etc. and that tune is way off for no other reason except you'll be pumping a ton more air into (and out of) the same engine. Again, an exaggerated example, but the same basic theory as a K&N, open lid, and nice breathing exhaust will be acting on my stock setup.

Hope this helps.
:)
 
M

Midnight 85

Guest
To narrow it down a bit further, I already had an afpr on my car before mods and even with 47 lbs. of pressure it still needed a custom burnt chip.
 
R

rel3rd

Guest
To narrow it down a bit further, I already had an afpr on my car before mods and even with 47 lbs. of pressure it still needed a custom burnt chip.

Yours definitely had some issues since I believe you said yours ran way lean even at idle. I "HOPE" I am ok in the low rpm, part throttle, and idle parameters as the O2's and everything else involved "should" make it close without any chip, but I guess I'll find out soon enough. :)

I have stayed away from chips ever since one of the Ford gurus dyno tuned a car for me a few years ago and I had nothing but headaches, but I recall that the GM vehicles always seemed to be a lot less forgiving and more receptive to chips so I may go with one on this car when the time comes that I need something.

BTW Vettefan 87, my 85 does not have pre-cats, just the one single cat after the front Y, which I recently replaced with a new high flow unit. sorry I missed that question first time around.
 
M

Midnight 85

Guest
I would think you should be okay, that's why I put might in parentheses in my first response. All I can say about responsiveness to a chip is to stay FAR away from any generic one and have one made for your particular mods. I have more mods than you, that is probably why mine was more sensitive.
 
Joined
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Messages
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Location
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Corvette
1987 Z52 Black Convertible
You're making me go where I shouldn't go, years ago I could have given you an intelligent answer but that was before computer controlled cars. Back then you would just up the jet size in the carb. What I can tell you is from my experience with my 85 L98. I had installed a VERY mild cam 3 years ago and had a Hypertech chip in the car that was there when I got the car. It ran fine until this past winter, I upgraded to aluminum heads, long tubes and a true dual exhaust. I also mildly ported the heads, intake and plenum. When I fired the car up to set timing etc. I glanced down and my brand new headers were glowing red. I spent the next 3 weeks chasing what I thought to be a vacuum leak to no avail, nothing was amiss there. I finally talked to Jesse Azzato, (Azzatochips.com) he went to great lengths to help me but in the end we both agreed I needed a different fuel curve, I was running lean, even at only 1,500 rpm. Jesse burnt me a new chip and the problem was solved, plus the car ran like never before. So, I'm not smart enough to give you actual particulars as to what leans them out when you make it breathe better except for what I said about needing more fuel. Maybe someone else here can do that that understands computer-ese. I just answered your post because I didn't want to hear of you ruining an engine. I hope this helps you understand.


Um with cam, head, intake work, and headers yes you would definetly need a tune on any car. But with headers no you don't if your car is in fine running order. I have been running headers on my car, and even open headers for a while with none of the effects you describe. I hope somebody will post that has similar mods....Hopefully Mad-Mic will see this...

I am in total agreement with you on the burning of a new chip. My brother has a 383 in his 86 with a TPIS Bigmouth manifold and ported heads, and a mild cam, with siamezed runners and a ported plenum, and that thing would hardly run with the old 20 year old tune on it.

Oh and if I would be in danger of ruining an engine it would of already happened. I have put about 8k on the motor with the headers on it with no chip tuning up until about a month ago. Not to sound cocky, just talking from experience...
 
M

Midnight 85

Guest
Oh and if I would be in danger of ruining an engine it would of already happened. I have put about 8k on the motor with the headers on it with no chip tuning up until about a month ago. Not to sound cocky, just talking from experience...

Read my first response, I never said he WOULD harm the engine, just that there is a possibility. What's wrong with giving a guy a heads up?
 
Joined
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Messages
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1987 Z52 Black Convertible
Read my first response, I never said he WOULD harm the engine, just that there is a possibility. What's wrong with giving a guy a heads up?

You said...

....I just answered your post because I didn't want to hear of you ruining an engine. I hope this helps you understand.

I have nothing wrong with giving anybody a heads up. I just do not agree that adding headers to a stock car NA 85 Corvette will make it run lean or have any adverse effects if installed properly.

Like I said before I am just speaking from experience, and I know others have done this as well. I have done all the free mods, descreened the MAF, TB bypass, 160 degree Tstat, advanced my base timing to about 12 degrees before TDC, ported my plenum. The mods I have actually purchased is the tune, and I have Breathless Ram Air, and also TPIS coated headers. I have run all the mods listed without the tune long before I actually got the car tuned if that makes any sense. Everything with the headers had been on the car for over a year, with no problems at all.
 
M

Midnight 85

Guest
Okay, I will try this in a simpler language, I NEVER stated rel3rd WOULD do damage, I said it MIGHT. A simple bit of advice so he could watch for anything amiss. Anybody who tells a person he can do a mod of any kind without changing some characteristic of the car is a damn fool. Go ahead and flame me back, I don't care, I am done on this subject.
 
R

rel3rd

Guest
Thanks guys. We're all here for the same reasons. Thanks for the replies. :)

I got my plenum today. Hope to get the headers in about two weeks, and when I get the runners and fuel regulator, I'll spend the weekend adding some power and see where I stand...
 
Joined
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Messages
2,240
Location
Northern Indiana
Corvette
1987 Z52 Black Convertible
Anybody who tells a person he can do a mod of any kind without changing some characteristic of the car is a damn fool.


So I take it you are saying that by any mod doing something like a coolant bypass, or adding a lower degree Tstat, or adding a different air filter, or something like an Air Foil needs the car to be reprogrammed because you are changing a characteristic of the car? The computers on the L98's are dinosours and very limited. Comparing it to the computer on a C6, or even a C5 for that matter is completely ridiculous.

I am in complete agreement with BIG mods, or "bulk mods". In meaning forced induction, nitrous, doing H/C/I, or something to that matter. Doing something minor and basic like porting and adding some headers, I just don't see it. The changes some of these mods make are so minute that the computer could really care less.

Sorry if I beat this into the mud. But I have been here for quite a while, and have followed in the footsteps of many others on here with the mods, and "tweaks" I have made to my 87.
 

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