test&tune:Tpis airfoil,52mm TB, adj. fuel reg.,flowmaster mufflers

[sothpaw]

Vettelt193,

Yes, I've been looking into exhaust.
People say you shouldn't do headers
before you do exhaust.
I'm also considering an MSD 6a ignition
and new racing wires--what do you think?

Exhaust changes scare me though, as I don't
want to make it too loud; the wife dislikes the car already.

Do you know anyone with dyno or
track tests before/after on the dynomax?
Increased horsepower, subdued sound,
and stock look is exactly what I would
look for. I've only seen credible evidence
that flowmaster muffs. lead to lower ETs.

The flowmasters (?and maybe other systems
also) seem to have resonance problems and
need a cross-over pipe. But it's guess work
as to where to put that...

--If I did flowmasters, I would get some LT1
mufflers from the junk yard and weld on the
tips. I like that look--it is unique.

--Mileage: I bought it with 42000, it probably had
45-47k for the dyno in '98. By the '99 dyno, it had may be
50k or just under that.

 

[Vettelt193]

well, here is the deal... you are lucky in having a '93 in one way, you can easily take the cats off, if you want to... I don't want to get into the debate of environmental issues here, but a car that only gets used a few thousand miles per year isn't going to kill off the world if it doesn't have cats... I would put in a 'test pipe' where the cats are, and keep them if you want to put them on later... Headers and exhaust in your setup will probably reduce horsepower because it will flow too much... I have seen dynomax numbers on stock engines and they are good for some horsepower... One of the vette magazines did an article on most of the exhaust systems a while back (vette or corvette fever) On yours, it should be good for more than just a few... They are a bit more 'throaty' than the stock mufflers, but no one would be suspicious... I don't even think your old lady would notice (the key is not to mention the swap, and make sure you are getting the dynomax that are supposed to be quiet)... Flowmaster, in my opinion, do not work well... they do the opposite of what a muffler should do... The tend to really increase sound inside the car, while the sound ouside the car is louder, it doesn't seem loud enough to warrant the huge interior increase... (this is due to a setup that bounces the sound back and forth, then it goes up and down, up into the cockpit of the car)

Another option (if money is less of an object) are the power effects exhaust... closed they run like stock, open they are loud and run like straight pipe... I honestly think they are ugly as can be, but I am sure there is a way to put an LT1 tip on those as well (the company may even do it for you)

Option 3--- the borla system for camaros and firebirds has removable plates that have holes in them... the plates make the exhaust go all the way through the muffler, or straight out with no muffler at all... you could put a short Y before each muffler, and cap it off with a metal plate... when you want to have it loud, take off the cap, quiet for the wife, put the cap back on... the benefit is the stock mufflers are so big, you should be able to hide it behind everything so you can even see it from the back of the car, a local muffler shop shouldn't charge more than 150 to do something like that

--MSD = waste of money... I have never seen a car perform better with one that is only mildly modified... They also tend to eat up spark plugs... I am talking 15k miles on bosch plat. plugs... If you get up to 400 HP it may be worth it. Until then, the stock system works just fine. put your money towards exhaust...

--Wires may help, but don't expect anything.... the stock wires aint bad either... the whole stock ignition system is pretty good...

--at 50k miles, and a 10 year old car, I would go for new plugs... Here is the deal... The plugs that GM sells are something like 8 bucks each... well, they work much better than bosch plat. (2 bucks? each)... something about the temperature range makes them so much better it is unreal... They will also probably last you until you rebuild the engine. I like that because they are so hard to get to on 92-96 vettes.

Well, there goes another long post exhaust is definitely holding you back right now though, I think so much so that the increased rocker isn't really doing much for you, as well as some of the intake work.

Also, since you have a hypertech chip, which should be a stage II chip, you may try going back to stock and seeing how the car runs... Hypertech is famous for advancing the timing too much... If your engine is slightly better than stock, the chip could take you over the edge on timing, effectively reducing HP... On the OBD computers, I have seen many cars run better in stage I mode than stage II, because the timing isn't advanced as much... superchips is much better and will custom make you a chip for a reasonable price... This will take into consideration the icreased rocker height, increased air intake, and possibly exhaust

 

[sothpaw]

Plugs--
Well, I replaced them with OE plugs
(tune up) when I bought the car--
tuning up the newly purchased, used car
is a custom my Dad taught me!
But... you think the OE plugs are better
than Boshe plat plus 4 plugs? everybody seems
to love these! They are like 6 bucks ea.

--car has 72 k mi today, so wires should go
as a matter of maintenance, I suppose.

--MSD: very interesting. So you have seen it
and it does nothing on stock cars? You could
be right. I have only 1 data point on it, and that
was in combo with other intake mods (bypass, airfoil,
intake, plus MSD got .4sec )

--hypertech: yes, I should try a stock one, but I am cheap.
During dyno. #2, The tech showed me the hp/Torq curves
and you can see tiny waves in the curve because the knock
sensor is actively fighting the computer (which I guess has
over-leaned the mixture!!!). But the car never knocks...
the knock sensor is winning! And I keep 93 octane gas in it.

--I'll have to do some research on dynomax then. If it was stock
look, no resonance, and it helped (.2?) I would do it in a heartbeat.

 

[Vettelt193]

I have worked with a handful of LT1 powered cars with MSD, and it never seems to make a noticable difference in speed... the only comment that ever gets made is the car seems to run a bit smoother... don't get me wrong, there is no doubt that MSD will make a stronger spark, it is just the factory system on LT1's is good enough... When I talk about this, it is from mildly modified to one car that had heads, cam, intake, gears etc. + 6 psi supercharger with no real difference (the guy with the supercharger cranked it up a notch and blew out the bottom end, once you get to 600 hp, the LT1 isn't too happy)

--I am trying to find the info on the quiet dynomax mufflers... I only had a few minutes this afternoon to look and didn't come up with anything (I am second guessing myself on the brand now, but i really thought it was dynomax)... I am sure I can dig up that sound/hp test that one of those vette mags did awhile back, it was on a 96 GS if anyone out there remembers?

--I have heard good and bad things about the plus 4 platinum plugs... I was going to go for them, but my corvette tech said he would gladly put them in, and he would gladly charge me a second time to change them out and put in the GM parts. (I do not, under any circumstances, enjoy changing the plugs on an LT1 or LT4, it is worse than rebuilding the whole top end of the engine when you have no lift) He told me quite frankly he has done many cars both ways, and the GM plugs are the only way to go (he does have other views on wildly modified cars) I can tell you many friends of mine change thier bosch plugs on a regular basis because their cars tend to not run right after awhile, where as my '93 had 100k+ on it with no problems at all... the choice is yours though...

--The .4 that the guy with MSD got came most entirely from the intake... the factory intake is a joke, and it is the first thing that should be removed from every C4 corvette!

--You may try an auto salvage yard for a stock chip... in the back of the corvette trader there is one called coastal corvetes (tiny ad, all text) they will probably sell you one for hardly anything, because no one wants them...

--ok, found some info on quiet mufflers... Walker Quiet Flow is what they are called... they look almost exactly (if not exactly) the same as the factory mufflers, supposed to sound the same, but flow more... I think anything you do to free up the exhaust would help big time... --- try just taking out the cats if you want to, that would do it for you as well... with 70k miles, you will notice a big increase in power without them

well, hope this helps again!

 

[-=Jeff=-]

Hey bob,

using your formula and my race weight of 3450 (89: No air bags or ASR) and a 1/4 info of 12.82@110 What is you calculated RWHP and BHP for my beast?

THANKS
-=Jeff=-

EDIT.. Oh yeah it is a 6spd w/3.45 gears

 

[sothpaw]

Vettelt193,

Can you embellish that sentence where
you mentioned that headers combined with
the exhaust would actually scavenge too much
gas out and so reduce hp?

--I would put on random technology's cats, I
can't remove them in MD since we have emmissions
testing and I don't want to mess with this every
2 years. Anyway, it sounds like as an experienced
tuner, you would recommend the exhaust at least
and maybe the bullet cats and exhaust?

--Do you think I could get .3-.4 from cats/exhaust
with my set up?

Thanks for all your info, you've saved me from
buying the MSD 6a. I've been unsure and putting
it off. I felt burned when I found out the hyper tech
chip doesn't help--I'm very wary of cheap horsepower!

 

[Vettelt193]

Jeff: you have yourself one heck of an engine! My calculation comes out to 312 RWHP, 367 at the crank, using the 15% loss again... this is using the MPH calculation, with such a low time, you could be running as much as 380 HP at the crank though... are you running good at the bottom end? I am guessing you have 367 HP, with a TON of low end torque, which is why the calculation seems off...

--headers + exhaust... The stock headers are already pretty good... (the F body cars have manifolds, not headers, so those stink) what happens is, the exhaust manufacturers have to make the aftermarket headers significantly 'better' to justify the high cost, the problem is, 'better' to them is much more flow... to a slightly modified engine, it comes out to too much flow when combined with a good exhaust... what I mean by too much flow is: your car needs some backpressure, if super free flow exhaust was the best, top fuel dragsters would have 2 inch long pipes coming off the engine, but they still have a good length of exhaust (and these guys run Huge HP) It is also really hard to justify the high cost of headers versus a good exhaust system... You will only flow as much as your weakest point... on a stock corvette, a good rule of thumb is to start at the very back of the car, and work your way to the front...(mufflers, resonator, cats, then headers) I would only go with headers on supercharged cars, or wildly modified cars that can really benefit. Otherwise, cars close to stock could actually lose power (especially on the bottom end)

--The reason why I suggested the cats was the low cost, and for sound... aftermarket cats will change your sound a bit, but not as much as taking out the center resonator... The plan was to keep interior noise down as much as possible... My guess, with the miles on your car, a set of high flow cats, and a good set of mufflers will shave a good .2 off the quarter mile... .3 to .4 if you lose the resonator too, and basically go cat back... I am just concerned for the high sound levels (usually this is easy, guys tend to want lots of sound, so they can just cut it all out)

--about hypertech... their products do work (on some cars) My guess is they don't test enough... As good as chevy has become at making engines with consistant power output, it still ranges +-5%.... Lets say hypertech got an LT1 with 300 HP, they do their tweaking and get it up to 315... now they can advertise 15 HP gain... the problem is, your LT1 may have come with 305 HP... their tweaking of the computer may be too much for your car.. so instead of getting 320 HP, you wind up with 290 HP because the computer is going beyond the engine's capabilities... I suggested the stock chip as a trial... some cars really benefit from the hypertech chip.. I have seen very good results... on the flip side, I have seen lower times with hypertech (and the lower times always seem to be on cars that ran a bit better than the rest)

--One more thing to think about... this is one mod that I really like... Underdrive pulleys... The kit you usually see is really expensive, but at www.enginedressshop.com, they have much better prices... On the LT1, you don't get a ton of power like you would on the L98 (the water pump is the biggest drag on the system, and LT1/4 cars it is direct drive off the cam) but, for 100 bucks, you can get the kit from this place (I haven't used them before, so I am not sure how good they are... they don't seem to make anything for the LT4's) The underdrive pulley kit is just 'free' HP in my mind... it should help everything out too... longer life for all the accessories, better gas mileage etc... On an LT1, a car with the pulleys can expect to run the same with the A/C on, as a stock car with the A/C off... (that is about what it feels like anyway)

 

[-=Jeff=-]

Jeff: you have yourself one heck of an engine! My calculation comes out to 312 RWHP, 367 at the crank, using the 15% loss again... this is using the MPH calculation, with such a low time, you could be running as much as 380 HP at the crank though... are you running good at the bottom end? I am guessing you have 367 HP, with a TON of low end torque, which is why the calculation seems off...

Bob,

Thanks for the engine compliment. As for the power I can only get a 1.9 or 2.0 60' out of the car. I had it dyno'ed on a Mustang Dyno last year (running rich) and it dyno'ed at 301 RWHP @5550rom and 340RWTQ at 3550rpm.

Here is a list of the goodies I have:
350 Shortblock .040" over bore
4-Bolt Main Block
ARP bolts Throughout
10.5:1 Compression (approx)
CNC Ported L98 Heads 2.00/1.57 valves
TPiS Mini-Ram with AFPR
Edelbrock/BBK 52mm Throttle Body
TPiS ZZ9 Cam Lift: .483/.520 duration @ .050 212/226 LSA 112
1.6i/1.5e Comp Cams Pro-Magnum roller rockers
24lb. SVO Injectors
MAT sensor relocation kit
Breathless Vortex Rammer
Custom PROM
Hooker Super Comp 1-3/4" Full Length Headers
2.5" Random Cats
Flowmaster LT1 catback.

Since last year I have changed to:

Homebrew Custom PROM
30lb. SVO Injectors
1991 Engine Harness and ECM
No Cats
Stock LT4 Cat-Back

I don't know what my power is yet but feeled stronger with the Speed Density tuning. I also need to swap out the Stock mufflers I feel they are too restrictive

 

[Vettelt193]

Jeff:, with your setup, the stock mufflers are really holding you back.. look for a big increase in HP with a good aftermarket set... How do you drive the car off the line? feather the clutch, or dump it? feathering it heavy will get you faster 60' times I would think... You should be down to 1.8 easy... hope this helps

 

[-=Jeff=-]

Jeff:, with your setup, the stock mufflers are really holding you back.. look for a big increase in HP with a good aftermarket set... How do you drive the car off the line? feather the clutch, or dump it? feathering it heavy will get you faster 60' times I would think... You should be down to 1.8 easy... hope this helps

Yeah I had the Flowmaster set up last year but it was a but on the annoying side.. I found a set of Stock looking straight through mufflers in Corvette Central I may try. They are only $230

I dump the clutch off the line.. I need to replace it next year though.

 

[sothpaw]

Bob,

What do you think of the MAT sensor relocation kit?
Will it drop the time even .05-.1 sec?

You mentioned aftermarket gears at one point--
someday I might go to 3.73s (when my existing
case goes, mechanic says it will be one year soon),
do you know what kind of time reduction I would get
out of that? .2s? .4s?

--Very interesting stuff regarding headers. You've done/
seen lots of LT1 vette mods eh? Your experience/knowledge
is exacly what every tuner needs; I realized long ago that
it's all about what the weak link is in the system. Trouble is,
it depends on what GM did that year: Did they put restrictive
mufflers on? or is the cat a bigger restriction? You have the
answer: muffler, then resonator, then cats, lastly headers.

--So to clarify, I could get .3-.4s out of mufflers/cutting the resonator
and cats, but it would be loud inside. Would a crossover pipe help?
I do favor cat-back systems--may as well go hole hog if you do it
at all. I just want it relatively quiet (not as much as stock though).

 

[jstkrsn]

I have a Hypertech Thermo Chip on my 92 LT1. I can tell no difference except for the fans coming on earlier. It is a piggy back assembly. Your stock chip plugs into the Hypertech one, then into the ECM. You can take it out and put the stock one back in any time. It only takes a few minutes. I'm thinking of doing the 1.6RR. I've heard of 15-20HP gains. All at high RPM's of course.

Jim


Borla mufflers, TB bypass, 51mm TB w/air foil, K&N, 160 Thermo, Cut air box, 315 rear tires, Taylor wires, Bosch +4's.

 

[sothpaw]

Jim,
That is the stage 2?
I asked my mechanic (not the guy who
put it in) to take it out and he said there
was only one chip, the hypertech one.
'92 is the same as '93 right?

Perhaps I will have to look into this myself...
Is it easy to open the ECM?

 

[jstkrsn]

Correct, it is the stage II. The ones I had bought before for my 86 vet and 87 Firebird were reprogrammed chips, but they were Traco and Jet brands. I could really feel the difference with them. The hypertech Chip I have now, the original chip plugs into it from the side, and then the whole thing plugs into the ECM. That leaves the portion of the chip that deals with normal engine functions untouched, and only the performance functions are bypassed and modified. That is what they emailed me. But like I said, I can't tell the difference. The air temperature seems to make more of a difference. I have one of those accelerometers, and some cool morning when I have time I will run a couple with and without. But the first one seems to always be the best, for the second and third the engine is hotter.

The ECM is really easy to get to on the 92. It's right obove the battery. Three bolts, turn it over and there is a small cover 2"x4" or so. Four screws and it exposes the chip. Then you just push on the clips to the side on either end, and they push it up. To put it back in, you push it in gently, then push the clips back towards the chip to lock it in. Can be done in five or ten minutes.