The Corvette catalogs provide ultra-basic training for 101 "students": i.e., add performance chip, lower temp thermo, and cat-back system to gain HP over factory config. I've already done the cat-back system, but I'm not sold on the thermostat change or the performance chip.

I'm interested in the 102 class. (This is still a beginner's class where the motor still retains a lot of the stock components). I'm curious what changes are worthless and which ones can provide a good bang for the buck. (Often HP gains translate into mileage gains. In my case, both aspects are worth discussing.)

1) Exhaust. If the precat/maincat configuration is replaced with high-flow (500+cfm) mini cats and the "Y" connections are replaced with true dual exhaust, what kind of improvement would be acheived? (Assume the use of free-flow mufflers). Can increasing the diameter of the pipe from the headers to the back of the car help also? (Assumes use of factory headers). What size is connector is on the factory header (outlet)?

2) Intake. If the stock manifold is retained, can the addition of a "performance" mass air flow sensor provide any improvement? This can include discussion of changes to the air box housing the air filter.

3) Chips. Noticed recent posts about custom tuning chips. Hypertech are pre-programmed aftermarker upgrades. Do they really help? Is the new guy recently referenced a better source for pre-programmed chips -- if you can't go to him and put your car on a machine? Would custom service (programming) be available in a metro area (like Kansas City)? Can the original chip be reprogrammed?

It is my feeling that the Corvette motor is partially designed to resemble a "racing motor". When you look at the manifolds, you see something more similar to a race car than a family car. And, replacing these items begins (what I consider) advanced modifications. Though these are modifications I could perform myself, I hate replacing relatively good H.P. parts.

That means this is still a beginner's course for those who want/wonder what improvements can be realized by getting more air into and out of the factory motor.

Thanks in advance to any "instructor" who chimes in!
Gregg

P.S. I would have included discussion of thermostat temps, but I've read enough about that (in here) lately. And, the pro's/con's don't seem to point to a clear winner.

 

If you live somewhere that gets pretty hot in the summer time, then a lower temp thermostat is the way to go. I would recomment a 185 degree thermostat and the the appropriate temp swith to turn on the fan at 200 and turn off at 185.

don't waste your money on the hypertech chip manure, because that's all they are.

when you have done some serious mods, then give alvin a call so that he can burn you a custom chip, alvin is at pcm for less, maybe he'll jump in later and give you some advice.

I think you are on the right track as far as your next mods, keep concentrating on improving the amount of airflow going to the engine.. I would definately get a k and n filter and clean up the maff for improved performance. a good perfomance tune up wouldn't hurt either.

getting true duals and full lenght headers for your car will give you alot of power for the money, but since you mentioned the minicats, i asume you want to stay smog legal, so full lenght headers are out of the question. so yes, get some high flow pre-cats and main cat and have your stock headers ported out. this won't give you as much power as the first configuration but it will give you a noticible difference.

if you do all these mods you're going to require a little more fuel, so an adustable fuel pressure regulator will help you a lot. add little more pressure.

tpis sells a kit that has alot of good parts in it, i think it's called a fast pack, it will have everything needed to vastly improve how much air your motor will take in.

ps i'm no instructor, just a guy who likes to go fast and burn rubber in his vet, i do all my own work.

 

I hope you don't mind me jumping in here with you. I have an "85", and I am wanting do some of the same type of mods as you. My car is stock except for muffler eliminators and a K&N filter and housing. Starting with exhaust. The general concensus here seems to be that long tube headers have a bigger gain than shorties. I have only been able to locate 2 companies that have coated long tubes for my car. Hooker and Hedman. If anyone else knows of any others, please speak up. Do the headers have the fittings for O2 sensors or do they need to be added to the pipes. I will probably go with dual pipes and not the "Y", and I might have to put mufflers back on it for the street.

I would go with the 185 thermostat if you are in a hot summer climate.

I was contemplating the hypertech chip too, but others have said it is not worth what you pay for it. If you can find someone to burn you a custom chip, would be money better spent.

Good Luck
Rock On

 

1) I've already got the fan switch (which I bet is more important than a new stat).
2) I've recently read (in here) that K/N filters clog up quickly -- bringing them down to lower performance levels.
3) What do you mean clean up the maff? (clean the wire)?
4) I wasn't planning on getting precats. Do I need them for sniffers?
5) Where do they do "performance tunes"?
6) Would I really need more gas pressure?
7) What about exhaust pipe diameter?
8) Asking for help from "instructors" just meant those with the "know-how"!


gp

 

I'd advice ordering TPIS' Insider Hints book (you can do it online) which is loaded with info and will answer many of your questions and give you a basic education of which things work and which ones don't. Excellent beginners book.

Hope this helps.

Jake

 

Hypertech chip (Thermomaster)-Turns my fan on earlier, no performance improvement

-Intake portwork (moderate throughout)from base to TB- +1.5 mph in 1/4 mile..

-Adjustable MAF,dont bother.
-K&N gains debatable, too much filter oil can screw up your MAF.
-Exhaust-Went to 2.5"front and rear "Y"s, 3" main, flos-Best improvement of anything Ive done so far. No longtubes, cant help ya there.

-All the cheap/free mods by themselves that are no good by themselves add up if you do enough of them and may enhance gains as internal mods/ci increase.
JMO, no documented proof though.

 

My thermostat opinion is on my website, as are further opinions of mine regarding mods.

Pipe size should be a minimum of 2.5" near the engine and ideally would decrease along the exhaust. The aftermarket headers you may use probably have something like a 3" outlet (2.25" stock), which you could pair with a 2.5"-2.75" pipe after the cats and going into your mufflers. Pick those based on sound alone. You do NOT want pipe size to increase as it travels rear, that will allow the gases to slow down and you want that port velocity to stay higher.

"performance" MAF, junk. Just cut the screens out of stocker.

Generic chips are worthless, only a custom tune should be done. I wouldnt do that until I was either completely done with my mods or I had changed the cam.

 

The key to a good exhaust system is free flowing, no blockages by cats or mufflers, and pipes that are not oversized. Larger pipes won't make up for having restrictions in the pipe. Punching out the cats is also a bad idea unless you weld a tube through there.


There's no excuse to go bigger than dual 2.5" with your rpms and displacement.

 

Thanks for the comments so far!

I really wasn't talking about changing out the headers, but I appreciate the thoughts in that regard. When I asked about pipe diameter, I meant exhaust pipe diameter (where I'd use factory headers, one cat per dual pipe, and one glass pack per pipe). I was told factory L98's had 2.5" pipe up front and 2.25" pipe after the cat. Interesting that Vader states exhaust SHOULD get smaller!

My personal thought is that the "Y' pipe through the main cat has to be a major restriction. If two 2.5" pipes are "Y'd" into a 3" pipe, 10 sq inches (of cross section) are being pushed through 7". That's one of the main reasons for my consideration of duals.

We don't have inspections (visual or sniffing) yet in Kansas, but I'd like to drive a reasonably environmental-friendly car. I figured two new high-flow cats would do a better job than the 17 yr-old original setup on my car (with 52K miles). Who thinks this wouldn't be a win/win alteration?

I'm also interested in plumbing side pipes (though the "fake" covers). That means I need to control emissions AND sound by mid car (where I'd turn the pipes outward to exit in front of the rear wheels. The alternative would be to put glass packs behind the covers which would require a 180-degree bend to accomplish. (I'll provide more explanation if required). Anyway, I'm guessing this is about the worst thing I could do. (I learned that bends create restriction when I ran exhaust pipe for my down-draft stove).

So, I have the opportunity to redo (improve) the exhuast -- making it cleaner and less restrictive during my quest to gain side pipes. This also led me to thoughts about improving the intake side.

Ultimately, I've heard you can't improve much without doing a lot, but some recent reading have led me to believe that some production considerations keep the STOCK motor from being all that it can be. I'm interested in learning more about those options before considering the installation of bigger headers/intake.

Thanks
gp

P.S. I gathered that a "performance tune" would involve hooking up a computer to reprogram the computer. Are places that do this readily available in most metropolitan areas? Would this be beneficial to look into with the (minor) types of mods I'm considering?

 

Personally, I think exhaust mods are WAY over-rated for most, relatively stock, performance engines, like the TPI that came in many of our Vettes.

Sure, if you've moved to some really high flowing heads, longer duration cam, SR or Mini-Ram, etc., exhaust mods make a bigger difference, but unless you've gone that route, I think exhaust mods should be lower on the priority list than a lot of other mods.

I've read Tech articles where back to back testing was done, well over $1,000 was spent on some "high tech" exhaust system with full length headers and those 'cool' FlowMaster mufflers and the engine only picked up 12 or so HP. Now, I said "only" because to spend over a grand for 12 HP isn't a lot of bang for the buck to my way of thinking

If you're looking to pickup 30 HP or more from just exhaust mods - like many ads use to promise - your stock exhaust would have to be extremely restrictive for the engine it's bolted to. Ours aren't really all that bad, relatively speaking.

Just the way I feel about it.

Jake

 

I disagree. Exhaust mods are a great way to free up that horsepower and get the engine breathing. On my 85 I DID feel the difference from the restrictive y pipe and single cat to true dual exhaust. I paid no where near $1000 for LT headers and my dynomax mufflers so my exhaust was money well spent and in fact are a strong base to work from for future mods. No sense in going all out on the intake side if you don't have the exhaust to exhale all that newfound energy. Always start with the basics and use what you have first. A good tune, fluids changed, and all adjustments made to sensors and tuneable parts per your factory service manual and you'll know what you have before spending the green. On TPI motors everything that I've read is the exhaust is highly restrictive however on the later year vettes their exhaust is much more flowable.

 

Exhaust mods can have a big sotp effect because they change off-idle torque, throttle response, and sound. It doesn't necessarily mean its adding any horsepower though.



btw Gregg, 2.25 + 2.25 = 3"

 

The torque is what I feel and I noticed a nice gain in torque which is where the TPI shines. I don't have actual numbers as I'm no drag racer but I felt it and that's what matters to me. Increase the torque and you are going to increase your fun!

 

I think reading and research is the best place to start. Jake mentioned the TPIS book which is good , VADER 86 on his web page pretty much goes through that and more for free. 65z01, and Nathan Plemons also have good and informative sites, you will find to make real gains, will take real parts, as GM's designs are pretty good.

I think that if you are looking at maybe one or two mods probably the best bang for the buck is to put NO2 on the car, other things to look at would be a gear (depending on what is in the car) and some intake work.

Set some type of goal in performance for yourself for a couple of reasons, A) after you start looking at this stuff setting a budget might be a good idea (unfortunately, real parts are not cheap for these cars), so you get things that really work and don't end up buying things that have no or very little effect. B) putting together a combination of proven things (intake, cam, exhaust) that will deliver performance. MY 02

 

My first recommendation for a TPI Vette is to start with Exhaust work.
Replace the entire Exhaust with the following items:

1. Long Tube Headers - this will eliminate the Precats.
2. Hi-flow Main cat or no Main cat at all.
3. Cat- back exhaust with high flow mufflers.

Vic

 

Gregg;

Are you going to have your exhaust custom fab'd or does someone make an H pipe for true duals, w/ or w/o a cat?

 

Does this mean the EXHAUST pipes directly connect to an L98 manifold are 2.25 (vs 2.5")? My original math (in my previous post) is based on 2.5" pipes. If the pipes are 2.25", your equation is closer to equal -- but not exact.

Pi(1.125)Squared = 4 sq" x 2 = 8 sq in for two 2" circles
Pi(1.5)Squared = 7 sq in. for a 3" circle

7 doesn't really equal 8. But -- if it's O.K. or even good to slighty increase pressure as you head to the back of the exhaust (as Vader indicates), then it would seem that the exhaust system can not be improved much without looking at headers/intake.

 

The front Y pipe is made up of 2 2.25" pipes, yes. The pipe connecting to the exhaust manifold is that small. The rear Y is the same size. The ports on the exhaust manifolds are tiny, which combined with elimination of the unnecessary precats, is why the headers improve the power so much.

 

I strongly suggest you listen to Vic. He has one of the best running LTR TPI setups on this forum. I have seen it many times at the track and it's very impressive.

 

If you add Longtube Headers, high flowing cat, free-flowing mufflers, well-sized and leak-free exhaust work, you should se BEYOND 30HP..
At least on early L98's..