Sigforty

So can someone explain to me exhaust pulse tuning and what factors can change the performance of an engine. I am looking at an issue I have with my car right now. It appears by being off with the exhaust pulse the engine will have reduced torque of the midrange. I have installed some cutouts on the car, and noticed they help increase my midrange when open due to allowing the pulse to exit before the mufflers. The car is a Corvette Z06 with LG pro headers and x-pipe with the stock Ti mufflers. The image below is dynojet results with the cutout closed and open.

WYATT318MOPAR

iTrader: (28)

The Closer To The Engine You Can Get Your Crossover Pipe The Better Off You Will Be At Eliminating Exhaust Gas Pulses In Your System...only Tru Way To Measure And See Where They Are Being Created Is To Remove What X Pipe Or Crossover You Obviously Have Now And Apply A Light Coating Of Black Gloss Paint To The Underside Only Of The Exhaust Pipe Section From About 10 Inches Back From The Headers Extending About 3-4 Ft..bring The Car To Normal Operating Temp And Take For A Short Drive Maybe 1-2 Miles The Pulses Will Cause The Section Of Pipe They Are Created In To Burn The Paint Off Way Before The Rest Of It..install The Balance Tube In The Center Of The Burnt Section The Use Oven Cleaner To Remove The Left Over Paint...this Is The Best And Most Fool Proof Way..maybe Not The Most Technologically Advanced But Tested And Proven...every Engine, Car, Combination Is A Little Different So Even Manufactured Aftermarket Pipes May Not Be Right For You Exact Application...hope That Helps You Out Man..

1989GTA

You need to do an internet search. Try "exhaust science vizard" for a good article and " exhaust terminator boxes".

Sigforty

I will try to look that up.

I got some information on the exhaust system from Larry Meaux who ported my heads. It appears that somehow I am on a bad length for the total exhaust system, and when I open the cutouts it allows the pulse to exit at a better time. All of this exhaust stuff has a relation to how the engine displacement and camshaft specs. Here is some of the stuff Larry showed me.

PipeMax calculates you need a 1.750" OD by 28.3" to 31.6" inches
so you are very close with current Headers

on the Collectors, PipeMax = 3.000" OD x 16.9" best

or 8.5" or 33.8"

the H-Pipe should be at = 16.9"
the X-Pipe should be = 67.7"

the "Worst Lengths" are
Worst HP/TQ Loss Collector Lengths= 25.4 , 50.8 , 101.5 , 203.1 inches long


-- Total Exhaust System Tuned Lengths (Primary ends to TailPipe end) --
Best HP/TQ Tuned Collector Lengths= 16.9 , 33.8 , 67.7 , 135.4 inches long

1989GTA

Larry is right there among the best when it comes to exhaust systems. I'm using Pipemax myself. Larry has given you some good free imformation.

Your collector or secondary pipe should be 3.00" in diameter and hopefully it is. Your total secondary exhaust length which you have listed at the very bottom of your post is what you need to use. The measurement starts at the end on the primary pipes in the collector and ends where your exhaust system ends in the atmosphere.

Ideally your cut out should be at 16.9" or one of the lengths mentioned at the bottom. For something really interesting and not needing a cutout do a search for exaust termination boxes.

Sigforty

Yea, it is hard to move stuff with the C5 exhaust system an retain ground clearance. Here are the measurements on what my exhaust looks like now.
My collectors are 11" long
The x-pipe is at 20"
The cutouts are placed right around 60"
The total exhaust system length is around 124". I only counted the muffler diameter once, but the c5 has a funny muffler setup. The mufflers are at 15.5 inches long.

The main thing is the amount of torque I gain in the midrange by having the right exhaust length.

ZMONSTER!

iTrader: (9)

Back from the dead!
I have a few questions about all this but for now what is the ideal length of an H pipe? Does the length of the crossover effect anything?

Sigforty

I have not heard anything about the length of the crossover, but I do know where it is placed will make a difference.

ZMONSTER!

iTrader: (9)

Ya I see that placement of the crossover is important but what about diameter and length? Anyone?

white2001s10

iTrader: (4)

Sigforty, what ever happened to your car?
Did you get things all worked out?

1989GTA

David Vizard had something on the crossover. I know he had a minimum. Maybe 1 3/4" or 2" for the diameter? Also there were some parameters on the length. Maybe a Google search for "David Vizard exhaust" would turn up the article.

ZMONSTER!

iTrader: (9)

Ive looked around but either I didnt see it or it didnt come up. I know the article I read had alot of info on it but I dont recall seeing anything regarding crossover specifics, or anything about cat placement.

1989GTA

Hmmmm, I know I read about it in one of David's articles. I was doing some research on exhaust termination boxes and came across it. Maybe it was on his website www.gofastnews.com

Update: I did a quick search and found where David sugested using 2" pipe to connect the exhaust termination boxes as an H pipe. I believe that confirms what I read in another one of his articles. I also think he said not to exceed 36". Again going by memory so don't take that as gospel.

ZMONSTER!

iTrader: (9)

Sounds good man appreciate the link!

Sid447

Balance/Cross-over Pipes or merge/X-pipes:

This is straight out of "How To Build Horsepower" by David Vizard
ISBN 0-931472-24-5.
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......."Extensive dyno work & highway testing has demonstrated that a simple crossover pipe -interconnecting the two sides of a dual-exhaust system just after the collectors & ahead of the mufflers- can increase engine power.
The power benefits of a cross-over pipe apply to both street & race cars, but the reason for power enhancement differs in each instance.
In an open exhaust race vehicle with a x-over between the collectors, the pipe transfers exhaust shock waves from one side of the system to the other.
With a street system, the x-over pipe performs an additional function: The x-over allows each side of the engine to partially share the combined muffler flow capacity.
Although, even the most effective x-over will not double system flow, improvements of 25% are common.
Crossover systems can be constructed in several different ways. The single, straight crossover is acceptable when muffler flow capacity is exceptionally high, but a double x-over system will increase performance if the mufflers are restrictive or engine output exceeds 350hp.
In simple terms, the more restrictive the mufflers, the more essential the x-over pipe becomes."
D.Vizard

In Summary about this modification:-

1]..."Prove 100% successful at reducing noise. Anywhere between 1 to 3 dB....
2] ..60% of cases on a dyno show a power increase of up to 12hp with 5 to 8 being normal....
3] ..40% of cases showed no change in power....
4] ..NO cases of any reduction in power.....
5] ..Length of balance pipe is not critical. Dyno test with pipes as short as 18" responded in the same manner as ones 72" long"...

D. Vizard
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**John Lingenfelter (RIP) says: "..Ensure balance pipe dia. is no less than 80% of main exhaust diameter...." (This was in reference to retro-fitting one to a true dual system without a balance pipe).

Sigforty

Well, by adding the cutouts I can see more of my potential under the curve increase as to without them. Not much I can do right now though due to lack of funding.

kelp

Just ran into this skimming along. Look, it's a pulse problem vs feedback into intake for sure. I had the same thing, and what got rid of the midrange trough is tuning it to run on MAF above 3000 vs 4000. Strange but true,that was the cure. Don't ask me why.