The Ford Barn

old31 · 06-02-2021, 03:20 PM

Does anyone know what the added HP would be for adding a 2nd carb and headers to an otherwise stock motor. No HC head.

BRENT in 10-uh-C · 06-02-2021, 03:29 PM

Quote:

Originally Posted by old31

Does anyone know what the added HP would be for adding a 2nd carb and headers to an otherwise stock motor. No HC head.

I can only speculate but likely only a couple of Hp, -if that.

Jack Shaft · 06-02-2021, 04:03 PM

If you only get 4 hp that's a 10% increase..header doesn't do much,Hick's exhaust manifold design is sound..

nkaminar · 06-02-2021, 05:35 PM

The header will not do much. The exhaust is pushed out of the cylinders and the stock exhaust manifold is large enough. A high flow muffler might help, especially if you have an aftermarket muffler that is restrictive.

However, the intake side can benefit from increased flow capacity. The air only has the atmospheric pressure to push it in. Adding a second carburetor and a manifold to match will help. This will only be felt at higher rpm. So if you are not going to race your stock engine you will not see much change. The stock engine will not take high rpm for very long. Look for increase of 7 horsepower. See http://www.rarecarrelics.com/tests-t...ord-engine.php.

The best bang for the buck is a higher compression head.

Pete · 06-02-2021, 10:25 PM

Quote:

Originally Posted by old31

Does anyone know what the added HP would be for adding a 2nd carb and headers to an otherwise stock motor. No HC head.

There is only one person that could know that and he rarely speaks.

old31 · 06-03-2021, 06:03 AM

Sponsored Links (Register now to hide all advertisements)

I should have been more specific. Sorry.

What is the increase in HP with a header that goes directly out an exhaust pipe with no muffler?

Jack Shaft · 06-03-2021, 07:31 AM

It depends on what else you do, extracting exhaust is only one piece of building a better air pump.. on a pure stock engine? negligible difference, probably not enough to accurately measure. Exhaust restriction isn't the core issue with stock model a engine performance.

chap52 · 06-03-2021, 07:43 AM

IMHO, better off just getting a HC head. Less to deal with. Chap

nkaminar · 06-03-2021, 07:52 AM

Warning: Technical discussion

When the exhaust valve opens there is a pressure pulse that travels down the exhaust pipe at the speed of sound. When it gets to the end it reverses as a negative pulse. The negative pulse will suck exhaust gasses out of the cylinder. The length of the exhaust pipe determines the timing of the scavenging and thus the rpm where it is most effective. In a race car you will find all the exhaust pipes in a header the same length and joined together with an added length of exhaust pipe (no muffler). The joined pipes reinforce the scavenging effect from each header pipe. A defusing cone at the end can widen the negative pulse and thus increase the effective rpm range.

Usually the cam is ground to take advantage of the scavenging effect. A stock Model A cam is not ground to use this scavenging. There may be some advantage but not like in a racing engine that has been designed for the scavenging effect.

The intake manifold can also be designed to take advantage of the pulses there. In this case there is a negative pulse that travels up the intake manifold and reverses as a positive pulse which helps push more charge into the cylinder.

the speed of sound in the exhaust and intake systems is dependent on the temperature of the gasses. It can be calculated but it ends up being cut and try for the final lengths and designs.

In a stock Model A engine getting the exhaust out is not a major issue, unless there is a restrictive muffler. Having an open exhaust header may help a bit but not much. I would guess maybe 2 horsepower, but that is just a guess.

ursus · 06-03-2021, 11:39 AM

Excellent explanation of scavenging, nkaminar! The level of restriction in the muffler has to have considerable effect on limiting the negative pulse.

Jim Brierley · 06-03-2021, 02:50 PM

You'd be wasting your money and time doing that to a stock engine. You would probably gain a small amount of power, but very little. It's the entire combination of things that give good results. A single carb such as the Stromberg 97, and higher compression will make an amazing difference. From experience I can tell you that on a stock engine, a 97 will outperform the smaller 81

updraught · 06-03-2021, 07:58 PM

Quote:

Originally Posted by Pete

There is only one person that could know that and he rarely speaks.

How will we know when he's spoken?

Ranchero50 · 06-03-2021, 08:53 PM

To expand on what nkaminar said. This is the exhaust on my '29 speedster build. Eventually being fed by a blown B engine. @40" long primaries for @2800 RPM peak torque paired by firing order (1-4,2-3) for even exhaust pulses into an X pipe that will pull a negative pulse on the other upstream paired pipe and share the exhaust pressure pulses between the downstream pipes as each exhaust pulse goes through the system. As built it's actually just about as quiet at idle as the stock exhaust. There's a good bit of science into making it work and just a little guesswork too.

Pete · 06-03-2021, 08:59 PM

Quote:

Originally Posted by updraught

How will we know when he's spoken?

You definitely will know.

johnneilson · 06-03-2021, 09:14 PM

Quote:

Originally Posted by Ranchero50

To expand on what nkaminar said. This is the exhaust on my '29 speedster build. Eventually being fed by a blown B engine. @40" long primaries for @2800 RPM peak torque paired by firing order (1-4,2-3) for even exhaust pulses into an X pipe that will pull a negative pulse on the other upstream paired pipe and share the exhaust pressure pulses between the downstream pipes as each exhaust pulse goes through the system. As built it's actually just about as quiet at idle as the stock exhaust. There's a good bit of science into making it work and just a little guesswork too.

The two up two down crank and 1423 FO will make the siamesed ports much more efficient and reduce the amount of reversion between cyls.
Not too sure why limiting to 2800 revs, a decent flathead design will go much higher.

J

Pete · 06-03-2021, 09:34 PM

4 intake ports will go over 6200.

johnneilson · 06-03-2021, 09:42 PM

Quote:

Originally Posted by Pete

4 intake ports will go over 6200.

7000 plus with the right valve setup...

mach0415 · 06-03-2021, 10:39 PM

This may help...
https://www.modelaparts.net/dynoshee...ynosheets.html

Pete · 06-03-2021, 10:48 PM

Quote:

Originally Posted by johnneilson

7000 plus with the right valve setup...

Yup, well over 7000 with 4 valve 34 degree pentroof Weslake head...

Bick in New Zealand · 06-04-2021, 04:50 AM

Quote:

Originally Posted by Pete

Yup, well over 7000 with 4 valve 34 degree pentroof Weslake head...

Never heard of that setup........ details?

06-02-2021, 03:20 PM	#1
old31 Senior Member Join Date: Jan 2016 Posts: 2,094	Added HP for 2nd carb and header? Does anyone know what the added HP would be for adding a 2nd carb and headers to an otherwise stock motor. No HC head.

06-02-2021, 04:03 PM	#3
Jack Shaft BANNED Join Date: Dec 2019 Posts: 1,196	Re: Added HP for 2nd carb and header? If you only get 4 hp that's a 10% increase..header doesn't do much,Hick's exhaust manifold design is sound..

06-02-2021, 05:35 PM	#4
nkaminar Senior Member Join Date: Jan 2012 Location: Western North Carolina Posts: 3,899	Re: Added HP for 2nd carb and header? The header will not do much. The exhaust is pushed out of the cylinders and the stock exhaust manifold is large enough. A high flow muffler might help, especially if you have an aftermarket muffler that is restrictive. However, the intake side can benefit from increased flow capacity. The air only has the atmospheric pressure to push it in. Adding a second carburetor and a manifold to match will help. This will only be felt at higher rpm. So if you are not going to race your stock engine you will not see much change. The stock engine will not take high rpm for very long. Look for increase of 7 horsepower. See http://www.rarecarrelics.com/tests-t...ord-engine.php. The best bang for the buck is a higher compression head. __________________ A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past. Last edited by nkaminar; 06-02-2021 at 05:44 PM.

06-03-2021, 06:03 AM	#6
old31 Senior Member Join Date: Jan 2016 Posts: 2,094	Re: Added HP for 2nd carb and header? Sponsored Links (Register now to hide all advertisements) I should have been more specific. Sorry. What is the increase in HP with a header that goes directly out an exhaust pipe with no muffler? Last edited by old31; 06-03-2021 at 06:16 AM.

06-03-2021, 07:31 AM	#7
Jack Shaft BANNED Join Date: Dec 2019 Posts: 1,196	Re: Added HP for 2nd carb and header? It depends on what else you do, extracting exhaust is only one piece of building a better air pump.. on a pure stock engine? negligible difference, probably not enough to accurately measure. Exhaust restriction isn't the core issue with stock model a engine performance.

06-03-2021, 07:43 AM	#8
chap52 Senior Member Join Date: Jun 2013 Location: Marana Arizona Posts: 1,776	Re: Added HP for 2nd carb and header? IMHO, better off just getting a HC head. Less to deal with. Chap

06-03-2021, 07:52 AM	#9
nkaminar Senior Member Join Date: Jan 2012 Location: Western North Carolina Posts: 3,899	Re: Added HP for 2nd carb and header? Warning: Technical discussion When the exhaust valve opens there is a pressure pulse that travels down the exhaust pipe at the speed of sound. When it gets to the end it reverses as a negative pulse. The negative pulse will suck exhaust gasses out of the cylinder. The length of the exhaust pipe determines the timing of the scavenging and thus the rpm where it is most effective. In a race car you will find all the exhaust pipes in a header the same length and joined together with an added length of exhaust pipe (no muffler). The joined pipes reinforce the scavenging effect from each header pipe. A defusing cone at the end can widen the negative pulse and thus increase the effective rpm range. Usually the cam is ground to take advantage of the scavenging effect. A stock Model A cam is not ground to use this scavenging. There may be some advantage but not like in a racing engine that has been designed for the scavenging effect. The intake manifold can also be designed to take advantage of the pulses there. In this case there is a negative pulse that travels up the intake manifold and reverses as a positive pulse which helps push more charge into the cylinder. the speed of sound in the exhaust and intake systems is dependent on the temperature of the gasses. It can be calculated but it ends up being cut and try for the final lengths and designs. In a stock Model A engine getting the exhaust out is not a major issue, unless there is a restrictive muffler. Having an open exhaust header may help a bit but not much. I would guess maybe 2 horsepower, but that is just a guess. __________________ A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past. Last edited by nkaminar; 06-03-2021 at 08:04 AM.

06-03-2021, 11:39 AM	#10
ursus Senior Member Join Date: May 2010 Location: Oregon Posts: 1,374	Re: Added HP for 2nd carb and header? Excellent explanation of scavenging, nkaminar! The level of restriction in the muffler has to have considerable effect on limiting the negative pulse.

06-03-2021, 02:50 PM	#11
Jim Brierley Senior Member Join Date: Jun 2010 Location: Temecula, CA Posts: 4,085	Re: Added HP for 2nd carb and header? You'd be wasting your money and time doing that to a stock engine. You would probably gain a small amount of power, but very little. It's the entire combination of things that give good results. A single carb such as the Stromberg 97, and higher compression will make an amazing difference. From experience I can tell you that on a stock engine, a 97 will outperform the smaller 81

06-03-2021, 08:53 PM	#13
Ranchero50 Senior Member Join Date: Aug 2019 Location: Hagerstown MD Posts: 224	Re: Added HP for 2nd carb and header? To expand on what nkaminar said. This is the exhaust on my '29 speedster build. Eventually being fed by a blown B engine. @40" long primaries for @2800 RPM peak torque paired by firing order (1-4,2-3) for even exhaust pulses into an X pipe that will pull a negative pulse on the other upstream paired pipe and share the exhaust pressure pulses between the downstream pipes as each exhaust pulse goes through the system. As built it's actually just about as quiet at idle as the stock exhaust. There's a good bit of science into making it work and just a little guesswork too. __________________ Building a '29 Speedster, the hard way...

06-03-2021, 09:34 PM	#16
Pete Senior Member Join Date: May 2010 Location: Wa. Posts: 5,407	Re: Added HP for 2nd carb and header? 4 intake ports will go over 6200.

06-03-2021, 10:39 PM	#18
mach0415 Senior Member Join Date: Jul 2011 Location: Chester, SC Posts: 162	Re: Added HP for 2nd carb and header? This may help... https://www.modelaparts.net/dynoshee...ynosheets.html __________________ Thanks, Mark in SC "We the unwilling, led by the unknowing, are doing the impossible for the ungrateful." -- By society, who is still arguing over who said it.