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cutout location

 
chrisaustria chrisaustria
User | Posts: 187 | Joined: 01/13
Posted: 05/05/14
02:51 AM

Hi!

I've ordered some QTP cutouts (2.5") for my 66 GTO. Where is the best position to install them? I did some research and hope for more hp on the drag strip.
I choose manual ones because I don't need them on the street and the electric cutouts are a source of leakage and other troubles I was told.

This is my car: https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-prn2/t1.0-9/10156001_4219059892103_7167230352728347328_n.jpg

What do you think?  

shyrgfuh3 shyrgfuh3
Enthusiast | Posts: 475 | Joined: 11/13
Posted: 05/05/14
03:31 AM

chris dude, what are you thinkin? your tires spin so bleepin bad now off the line, more hp will make your car slower, lol.

you need TRACTION.

your car might get leaner with them open.  

chrisaustria chrisaustria
User | Posts: 187 | Joined: 01/13
Posted: 05/05/14
03:42 AM

I don't think I can get more hp at low rpm's, so it won't really make a difference with traction I guess. For traction I got the big Nitto Drag Tires now.

I did some maths.. again Smile My 2.5" dual pipes have a max. flow of 1000cfm. My mufflers only flow about 500-600cfm. I'm no exhaust expert but I have reason to believe that I will loose some power at higher rpm's because of a restriction in exhaust flow.

There are now 2 sollutions... get better flowing mufflers like Hooker Max Flow (they flow about 500cfm each!) or get cutouts. I decided to try cutouts first, but I'm not sure if they should be before or after the H-Pipe. A H-Pipe is good for power, so probably it's better to use them between H and mufflers?!  

chrisaustria chrisaustria
User | Posts: 187 | Joined: 01/13
Posted: 05/05/14
03:55 AM

my maths if you are interested:

- every in² of straight pipe can flow about 115cfm
- 2.5" pipes have 4.4in² that equals to about 500cfm
- 2x2.5" pipes without bends flow 1000cfm... with bends let's assume it's reduced about 20% to 800cfm
- my mufflers flow 250-300cfm each
- on the intake side there is a 750cfm Holley and a taperd spacer

So if my carb isn't way to big the exhaust will need to flow the full 800cfm at high rpm to make the most power, but my mufflers limit it to max 600cfm. The use of cutouts will eliminate the restriction from maybe 4000-6000rpm. I have no proof of my arguments, but it's only $100 to try. But even with all the maths I don't know where to place the cutouts.

The reason why I don't get better flowing mufflers to make the power all the time is: Sound... I really like the Flowmasters and I don't need some extra hp on the street because they won't be used.. with cutouts I can keep costs low, keep my Flowmaster Sound that I like and get rid of the restriction in flow on the stip.  

shyrgfuh3 shyrgfuh3
Enthusiast | Posts: 475 | Joined: 11/13
Posted: 05/05/14
03:57 AM

it doesn't matter in this case because you have single pipes until they meet the h pipe now. all you will be doing is letting the exhaust out before the h pipe.

you still need to be concerned about running it lean. i would not just stick them on then leave the jetting as is.


SPACER - If you can run a taller one, i would do that.

TIRES- The race ones will help a little but they will not work miracles.  

chrisaustria chrisaustria
User | Posts: 187 | Joined: 01/13
Posted: 05/05/14
04:09 AM

The H Pipe is there to balance the exhaust pulses for a better flow. But with open cutouts there is no restriction in flow so it may not be necessary to use it.
Maybe someone tried them before and after the crossover and can tell me if there is a difference.

After the H-Pipe the ground clearance is better.. if it doesn't matter where to place them I'll place them in front of the mufflers at position 2 on the pic.  

chrisaustria chrisaustria
User | Posts: 187 | Joined: 01/13
Posted: 05/05/14
04:15 AM

My carb now runs a little rich. At high rpm's it's still about 12:1 AFR. I wanted to change that but maybe I'll keep it as it is and try what happens with the cutous. I can connect the sensor on the track and see if AFR is higher with open cutouts.

The spacer is 1"... 2" will not fit.  

shyrgfuh3 shyrgfuh3
Enthusiast | Posts: 475 | Joined: 11/13
Posted: 05/05/14
04:22 AM

The H Pipe is there to balance the exhaust pulses for a better flow. But with open cutouts there is no restriction in flow so it may not be necessary to use it.

drag cars do not use cross overs so there's that answer.



Maybe someone tried them before and after the crossover and can tell me if there is a difference.

not a chance and if so it would not be back to back on the track or dyno so the results might not be helpful


before the h pipe is better but there's not a ton of difference.


100 lbs of sand bags in the trunk might help more.  

chrisaustria chrisaustria
User | Posts: 187 | Joined: 01/13
Posted: 05/05/14
04:42 AM

That's an interesting fact that drag cars dont use crossovers. So I'll try to use them after the headers and only put them back if there is a problem with ground clearance.

Last time I removed the spare wheel.. maybe that was a mistake.  

chrisaustria chrisaustria
User | Posts: 187 | Joined: 01/13
Posted: 05/05/14
04:47 AM

Another question.. how is a drag racing exhaust designed? On real drag cars? And how will open headers affect low end Performance?  

shyrgfuh3 shyrgfuh3
Enthusiast | Posts: 475 | Joined: 11/13
Posted: 05/05/14
04:56 AM

hello

these days its designed on computers and tested with a few different variants on a dyno on the engine it will be used on.  

tuffnuff tuffnuff
Moderator | Posts: 2567 | Joined: 12/09
Posted: 05/05/14
08:28 AM

Here is an interesting article on exhaust.

http://www.popularhotrodding.com/enginemasters/articles/hardcore/0505em_exh/viewall.html

Smile  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

chrisaustria chrisaustria
User | Posts: 187 | Joined: 01/13
Posted: 05/05/14
03:57 PM

Very interesting, thank you Tuff!  

chrisaustria chrisaustria
User | Posts: 187 | Joined: 01/13
Posted: 05/28/14
05:15 AM

I did it... installed QTP cutouts:

Video before - after:
https://www.youtube.com/watch?v=WOTjcHib_0Y  

shyrgfuh3 shyrgfuh3
Enthusiast | Posts: 475 | Joined: 11/13
Posted: 05/28/14
08:29 AM

hi chris;

your links do not work for me. the previous drag race video did.  

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