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.

Re: Added HP for 2nd carb and header?
 

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

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..

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.

Re: Added HP for 2nd carb and header?
 

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

Re: Added HP for 2nd carb and header?
 

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?

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.

Re: Added HP for 2nd carb and header?
 

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

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.

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.

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

Re: Added HP for 2nd carb and header?
 

How will we know when he's spoken?

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. :D

https://i.ibb.co/yB5w9p8/IMG-20210531-203008-565.jpg

Re: Added HP for 2nd carb and header?
 

You definitely will know.

Re: Added HP for 2nd carb and header?
 

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

Re: Added HP for 2nd carb and header?
 

4 intake ports will go over 6200.

Re: Added HP for 2nd carb and header?
 

7000 plus with the right valve setup...

Re: Added HP for 2nd carb and header?
 

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

Re: Added HP for 2nd carb and header?
 

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

Re: Added HP for 2nd carb and header?
 

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