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Intake and exhaust ideas/recommendations...

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ViperXAC
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Joined: September 9th, 2021, 3:59 am
Stroker Displacement: 4.6
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Vehicle Make: Jeep
Vehicle Model: Wrangler

Intake and exhaust ideas/recommendations...

Post by ViperXAC » September 9th, 2021, 4:09 am

I'm in the process of swapping in a 4.6 stroker from Carolina Machine Engine.
The cam they're using is a Comp Cams X250H-14 which is 206/212 duration at .050 and .460/.476 lift, 113 LC.

So far, I'm planning on running a cowl intake from THOR to a Leigh Performance 62mm throttle body into a 2000+ intake.

For the exit side, a Banks header to 2.5" pipe with high flow cats. and a 2.5" in 2.25" out muffler.

Does this sound like it will breathe well and keep the torque curve around 2-3k rpms?

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Cheromaniac
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Re: Intake and exhaust ideas/recommendations...

Post by Cheromaniac » September 9th, 2021, 11:46 pm

Yup, that sounds like a nice combo. A 4.6L stroker making up to 250hp needs a 2.5" exhaust minimum. A 62mm TB is fine and you could go even bigger.
1992 XJ 4.6 Stroker - 5MT - Stroker build-up, Stroker "recipes" Sold :cry:
2006 Mustang GT - 5MT - Modded
midlife crisis car. :D

Russ Pottenger
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Re: Intake and exhaust ideas/recommendations...

Post by Russ Pottenger » September 10th, 2021, 9:54 am

Just curious, why would you run a 2.500 exhaust up to and including the muffler but restrict it to 2.250 exiting the muffler?

ViperXAC
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Stroker Displacement: 4.6
Vehicle Year: 1997
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Vehicle Model: Wrangler

Re: Intake and exhaust ideas/recommendations...

Post by ViperXAC » September 13th, 2021, 11:13 am

Russ Pottenger wrote:
September 10th, 2021, 9:54 am
Just curious, why would you run a 2.500 exhaust up to and including the muffler but restrict it to 2.250 exiting the muffler?
My reasoning behind knocking the exhaust diameter down at the tail pipe is to keep velocity up to assist in scavenging.

Same idea with only going with the 62mm TB, I know it will have less of an effect because of the plenum and runners on the intake, but my goal is to keep peak torque low in the RPM range and from my reading/research so far velocity is more important for torque than volume.

Randy Bobandi
I think I'll order a "tab"
I think I'll order a "tab"
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Re: Intake and exhaust ideas/recommendations...

Post by Randy Bobandi » September 13th, 2021, 4:40 pm

ViperXAC wrote:
September 13th, 2021, 11:13 am
Russ Pottenger wrote:
September 10th, 2021, 9:54 am
Just curious, why would you run a 2.500 exhaust up to and including the muffler but restrict it to 2.250 exiting the muffler?
My reasoning behind knocking the exhaust diameter down at the tail pipe is to keep velocity up to assist in scavenging.

Same idea with only going with the 62mm TB, I know it will have less of an effect because of the plenum and runners on the intake, but my goal is to keep peak torque low in the RPM range and from my reading/research so far velocity is more important for torque than volume.
That is maybe the most common misconception of fluid dynamics. At least in relation to combustion engines. You can not apply Bernoulli's equation to the turbulent flow of engine exhaust or intake air charge. Bernoulli's equation or the venturi effect is only applicable to laminar flow or "linear flow". This is why you see straight pipe, open headers on drag cars. If pressure drops worked on engine intakes and exhaust, you would see it on every production vehicle. You don't, you never will. Pressure drops (decreases in cross sectional area) within intakes and exhaust will only be restrictive to mass flow rate.

ViperXAC
Posts: 3
Joined: September 9th, 2021, 3:59 am
Stroker Displacement: 4.6
Vehicle Year: 1997
Vehicle Make: Jeep
Vehicle Model: Wrangler

Re: Intake and exhaust ideas/recommendations...

Post by ViperXAC » September 13th, 2021, 6:02 pm

Randy Bobandi wrote:
September 13th, 2021, 4:40 pm
ViperXAC wrote:
September 13th, 2021, 11:13 am
Russ Pottenger wrote:
September 10th, 2021, 9:54 am
Just curious, why would you run a 2.500 exhaust up to and including the muffler but restrict it to 2.250 exiting the muffler?
My reasoning behind knocking the exhaust diameter down at the tail pipe is to keep velocity up to assist in scavenging.

Same idea with only going with the 62mm TB, I know it will have less of an effect because of the plenum and runners on the intake, but my goal is to keep peak torque low in the RPM range and from my reading/research so far velocity is more important for torque than volume.
That is maybe the most common misconception of fluid dynamics. At least in relation to combustion engines. You can not apply Bernoulli's equation to the turbulent flow of engine exhaust or intake air charge. Bernoulli's equation or the venturi effect is only applicable to laminar flow or "linear flow". This is why you see straight pipe, open headers on drag cars. If pressure drops worked on engine intakes and exhaust, you would see it on every production vehicle. You don't, you never will. Pressure drops (decreases in cross sectional area) within intakes and exhaust will only be restrictive to mass flow rate.
See sections 6 and 7 here. https://www.hotbikeweb.com/understandin ... ies#page-6
See 4th set of lines down begining with "Small runners..." https://help.summitracing.com/app/answe ... ner-volume
Have a read of this whole article. https://www.motortrend.com/how-to/ctrp- ... aust-size/

I have spent the last two months reading articles and looking at dyno graphs concerning intake and exhaust. Every forum thread similar to this one has a response similar to yours. Check out a dyno graph for a dragster and look at where the torque high point is, I don't want to have to run up to 5k rpms to hit my torque peak. I want my torque peak down where its useable near 3000-3500k. To do that, I need to keep velocity up in both the intake ans exhaust tracks.
You cant compare a dedicated drag engine to a daily driver.
Also, im pretty sure almost every production car's intake reduces in size before entering the intake manifold. The stock 4.0 throttle body reduces from 62mm to 58mm, wonder why that is.

Randy Bobandi
I think I'll order a "tab"
I think I'll order a "tab"
Posts: 40
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Re: Intake and exhaust ideas/recommendations...

Post by Randy Bobandi » September 13th, 2021, 7:11 pm

ViperXAC wrote:
September 13th, 2021, 6:02 pm
Randy Bobandi wrote:
September 13th, 2021, 4:40 pm
ViperXAC wrote:
September 13th, 2021, 11:13 am
Russ Pottenger wrote:
September 10th, 2021, 9:54 am
Just curious, why would you run a 2.500 exhaust up to and including the muffler but restrict it to 2.250 exiting the muffler?
My reasoning behind knocking the exhaust diameter down at the tail pipe is to keep velocity up to assist in scavenging.

Same idea with only going with the 62mm TB, I know it will have less of an effect because of the plenum and runners on the intake, but my goal is to keep peak torque low in the RPM range and from my reading/research so far velocity is more important for torque than volume.
That is maybe the most common misconception of fluid dynamics. At least in relation to combustion engines. You can not apply Bernoulli's equation to the turbulent flow of engine exhaust or intake air charge. Bernoulli's equation or the venturi effect is only applicable to laminar flow or "linear flow". This is why you see straight pipe, open headers on drag cars. If pressure drops worked on engine intakes and exhaust, you would see it on every production vehicle. You don't, you never will. Pressure drops (decreases in cross sectional area) within intakes and exhaust will only be restrictive to mass flow rate.
See sections 6 and 7 here. https://www.hotbikeweb.com/understandin ... ies#page-6
See 4th set of lines down begining with "Small runners..." https://help.summitracing.com/app/answe ... ner-volume
Have a read of this whole article. https://www.motortrend.com/how-to/ctrp- ... aust-size/

I have spent the last two months reading articles and looking at dyno graphs concerning intake and exhaust. Every forum thread similar to this one has a response similar to yours. Check out a dyno graph for a dragster and look at where the torque high point is, I don't want to have to run up to 5k rpms to hit my torque peak. I want my torque peak down where its useable near 3000-3500k. To do that, I need to keep velocity up in both the intake ans exhaust tracks.
You cant compare a dedicated drag engine to a daily driver.
Also, im pretty sure almost every production car's intake reduces in size before entering the intake manifold. The stock 4.0 throttle body reduces from 62mm to 58mm, wonder why that is.
The articles that you posted only mention mass flow rate (engine displacement x cross sectional area) and its effect on power per RPM. That's common knowledge and not at all in question. Nobody is putting 3" primaries on a K24 Honda. You may be confusing two different principles here.

What you mentioned in an earlier post was that you decreased the cross sectional area of your tailpipe to increase the exhaust gas velocity. That leads me to believe that you thought Bernoulli's equation would aid in scavenging. What you did there was simply restrict the flow of your exhaust gasses. Bernoulli's principle is not applicable to exhaust gasses leaving a combustion engine. It is not applicable to intake air charge either. The flow of fluid must be linear in order to achieve the venturi effect. Intake air and exhaust gas is wildly turbulent. Therefor it is crucial that combustion engine's intake and exhaust ducts be as free of obstruction and changes in cross sectional area as possible.

I mentioned top fuel cars as an example. That's the pinnacle of automotive engineering where engines must operate at peak efficiency.

Also, any decrease in diameter at the throttle body is simply to allow the intake tube slip over the throttle body flange. The ID of Jeep engine intake tubes and throttle bodies are virtually the same. Not even close to having any effect on the mass flow rate of a turbulent air charge.

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Cheromaniac
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Re: Intake and exhaust ideas/recommendations...

Post by Cheromaniac » September 13th, 2021, 11:39 pm

ViperXAC wrote:
September 13th, 2021, 11:13 am

My reasoning behind knocking the exhaust diameter down at the tail pipe is to keep velocity up to assist in scavenging.

Same idea with only going with the 62mm TB, I know it will have less of an effect because of the plenum and runners on the intake, but my goal is to keep peak torque low in the RPM range and from my reading/research so far velocity is more important for torque than volume.
There's absolutely no point in using a 2.25" tailpipe as there's no scavenging effect by the time the exhaust gases get there. Just go 2.5".
FWIW my 4.6 stroker made peak torque at 3500rpm, with 90% of that available at just 1500rpm. The front half of my exhaust system was 3" in diameter (2.75" at bends) and the rear half was 2.5".

https://www.angelfire.com/my/fan/Exhaust.html

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Re: Intake and exhaust ideas/recommendations...

Post by 275/350 I-6 » September 17th, 2021, 6:38 am

[/quote] There's absolutely no point in using a 2.25" tailpipe as there's no scavenging effect by the time the exhaust gases get there

https://www.angelfire.com/my/fan/Exhaust.html
[/quote]

That’s what I was thinking, at the muffler exit & tailpipe, it is to far down stream for any scavenging effect, the exhaust is simply being pushed out at that point, hence the larger diameter recommend.

From another point of view, I don’t think there would be a measurable amount of power loss to downsize the diameter like you described. If you already have the exhaust in that configuration I would run it, but if I was starting from scratch, like I just did with my 4.7 build. I would go 2.5” from the header collector through the hi flow cat, and muffler, all way to the end on the tail pipe at 2.5”.

275/350 I-6
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Posts: 55
Joined: February 4th, 2020, 8:48 pm
Stroker Displacement: 4.7
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Vehicle Make: AMC
Vehicle Model: CJ-7
Location: NC

Re: Intake and exhaust ideas/recommendations...

Post by 275/350 I-6 » September 17th, 2021, 6:41 am

[/quote]

There's absolutely no point in using a 2.25" tailpipe as there's no scavenging effect by the time the exhaust gases get there

https://www.angelfire.com/my/fan/Exhaust.html
[/quote]

That’s what I was thinking, At the muffler exit & tailpipe, it is to far down stream for any scavenging effect, the exhaust is simply being pushed out at that point, hence the larger diameter recommend.

From another point of view, I don’t think there would be a measurable amount of power loss to downsize the diameter like you described. If you already have the exhaust in that configuration I would run it, but if I was starting from scratch, like I just did with my 4.7 build. I would go 2.5” from the header collector through the hi flow cat, and muffler, all the way to the end on the tail pipe at 2.5”.

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