Better exhaust or new cam?

[Excaliber]

I run side pipes that are bolted to the collector with four bolts. On track day it's quick to simply unbolt and remove them and run open headers. I bolt on a short extension with a turn out to direct the "flames" away from the body.

The more horse power and flow you have the greater loss of horse power you will have from restrictive exhaust. In my case, 427 with 428 crank and solid roller cam that would turn up to 7,000 rpm, the side pipe loss was 97 horse power.

At the track I don't run air cleaners (2X4 intake) and also run bigger jets in the carb. With no air cleaners and open exhaust you need to increase the jet size to compensate for the additional air flow in and out. On the street, smaller jets, air cleaners, side pipes and I STILL can seldom go to wide open throttle due to traction issues. On the track, road race slicks are a must have for my setup.

[Tommy]

Jon,
Often, the key to getting the best answer is to ask the right question. You asked, "Which is a better way to get more hp....a bigger cam or different mufflers ...." I'm not certain that is the question you really want answered. Perhaps the question should have been, "What is the most cost effective way to make my car feel more powerful in street driving without giving up much comfort or drivability?" The answers to those two questions would be very different. For example, opening the exhaust would likely be the best answer to the first question if you were planning to use the car only on the track, but it wouldn't fare well as an answer to the second question. Perhaps you can refine your question and expand on why you are asking. I think that will get you better answers.

[saltshaker]

I recently changed carbs from 450 mech to 600 vac and there was a hudge difference....no bog vs tires that broke loose, but I still felt the motor could be more responsive. I also have driven the car on several trips of over 200 plus miles a day and the noise can be a problem( my ears ring all the time)... So when I thought about a motor that could be more responsive and had read about how restrictive the side pipes were I also thought that maybe a under the car exhaust might be less restrictive and give me more hp and move the noise from below my ears. With a muffler change in the side pipes maybe I could accomplish the same thing! As for air cleaners, I'm using Stelling & Helling....no room to go up!
Jon

[MaSnaka]

I have a 390fe which had a very dissapointing dyno run. After learning my side pipes and intake manifold were of the restrictive type thats all I changed. First the intake and the car ran very bad with my sidepipes. Then after changing the sidepipes to rare irons 2.5 dia mufflers the car picked up 70 hp on the dyno. My cam is about the same as yours. I also use stock iron heads D2TEA. I'm a believer in what has been said. It's important to get the A/F mixture correct too.

John

[vector1]

Originally Posted by saltshaker

Which is a better way to get more hp....a bigger cam or different mufflers for the side pipes or maybe exhaust under the car with low restrictive mufflers....fe headers are available to run the exhaust under the car, they look like Sanderson Headers but made by Hurricane at a reasonable price. Which would be the bigger gain? Any suggestions on the mufflers or cam? Currently using a Comp 282s ....

Jon

depends which one is more restrictive

[saltshaker]

Anyone using them and how did they change the sound and the noise level of your motor(FE)....has anyone done a dyno comparison to see the gain?
Jon

[Excaliber]

Don't be confused by the oft repeated "need for back pressure" to increase horse power. If that were the case, you would never see "open headers" on a race car.

The length of a header collector, in some cases, has an optimum length. One way to find it is to look carefully at the scorch marks or some other method that shows the temperature of the exiting exhaust gases. Then start cutting off the collector length until it just reaches the desired point, right at the highest temp exit point.

A two cycle engine certainly has a required "back pressure" point because of the nature of a two cycle. A properly tuned "expansion chamber" uses the escaping momentum of the exhaust to help "pull in" the fresh intake charge. That works best at near max rpm range. To some extent, this also applies to a four cycle, but not nearly as much and the "expansion chamber" becomes the "collector" on the end of the headers. No mufflers, in either case will add anything to the scavenging affect.

[RestoCreations]

A couple of points
-You will see a nice hp increase when changing from a restrictive manifold or header to a more free flowing 4 into 4 or long tube header system if you have a high hp engine. If you dont have a high hp engine, you are not going to see much of a change at all. Like was mentioned above, air in and air out. If your cylinder heads, intake, and cam are not up to par, then i would start there.

-I have seen some of these pipes that have a muffler with a flat face and then the flow hole in the center. This causes the air to hit that area like a brick wall. Its a dam, not a bottle neck. In that case, what really needs to be done is to make sure that area has a smooth transition. You can cut the muffler apart and create a smooth transition at that point. However, this requires a lot of work and might not be a project you want to tackle. Im not sure if anybody makes them with a smooth transition or if they just try to compensate the loss caused by the dam by making it smaller with a larger Internal Diameter muffler. I personally prefer the smaller internal diameter mufflers, but only if the hp loss is reasonable. I will take a 20hp flywheel loss any day over hearing loss. Look at the classic chambered website-he has a picture of reducers that make for a smooth transition-that is key. Now if only someone offered an option for 2-1/4 and 2" muffler section that would be nice.
-The louvers do catch the air when turned the correct way and make the pipes quieter/deeper, but you will also get a lot of back popping under deceleration.
-The larger louvers shown above will give a much better and deeper sound when faced the right way. The smaller louvers give the exhaust a higher pitched sound.
-The longer muffler section you can use without making the car look odd, the better.

Dwight-do you still have those inserts or did you toss them?

[xlr8tr]

more food for thought: if you have 4 header pipes at 1.75 inches internal diameter each, thats a total cross section area area of 9.6 square inches. A 2 1/2 inch ID muffler = 4.9 sq in, (no wonder there is a flow restriction) whereas a 3 inch ID muffler = 7.1 sq in, a 44% increase in cross section area, but still much less than the 4 header pipes. Although there is probably a bunch of fluid dynamics math thats way over my head to add to this...

[CobraEd]

Originally Posted by xlr8tr

more food for thought: if you have 4 header pipes at 1.75 inches internal diameter each, thats a total cross section area area of 9.6 square inches. A 2 1/2 inch ID muffler = 4.9 sq in, (no wonder there is a flow restriction) whereas a 3 inch ID muffler = 7.1 sq in, a 44% increase in cross section area, but still much less than the 4 header pipes. Although there is probably a bunch of fluid dynamics math thats way over my head to add to this...

Ahhh, . . but each pipe only fires and expells exhaust when that cylinder fires. It is not continual flow. Therefore the four pipes on the one side of the car share or contend for the flow volume of the muffler. They are not all flowing at the same time.

On the opposit end for induction, all eight cylinders do not draw air through the carb at the same time. They contend for it, each taking a turn.


There is a 47 page formula that explains this. I used to have it, but my dog ate it !!!


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[xlr8tr]

excellent point cobraEd! I knew there were smarter people than me here!

[undy]

Actually, as the exhaust gases flow through the system they cool and tend to shrink in size as they move, making the exit gases a bit slower than the entry gases.

[CobraEd]

Originally Posted by undy

Actually, as the exhaust gases flow through the system they cool and tend to shrink in size as they move, making the exit gases a bit slower than the entry gases.

I agree, but as stated, that is a function of the exhaust cooling, not due to the muffler storing the exhaust.


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