I wish I could figure out how to post the picture, but the link will just have to do. This link is from a post by ZL1powr showing his dyno time with Hooker Super Comp 2 1/8 undercar headers (no mufflers - green line) as well as his Hooker 2 1/8 side mount headers (no mufflers - red).

http://forums.corvetteforum.com/show....php?t=1021019

This dyno time shows a variety of information (ie, he looses no power with his custom made glasspack mufflers), but it does bring up an interesting point on which I would like to get some opinions.

It is interesting to me that when you just compare the headers with no mufflers, the undercar header offers more power above 5,500. The difference becomes pronounced at 6,200 when the dyno run is stopped. My initial thought would be to wonder what that difference would look like at 7,000 rpms (he does have a solid roller in there).

I have been considering the side pipes for sometime now but here in my concern. I have a high strung 468 solid roller motor in my vette that really does like to turn some RPM - pulls all the way to 7,000 when I want it to. It is my knee jerk to keep the undercar headers on for now and keep ALL of the high rpm performance advantages. I would put the sidepipes on when I install a larger displacement motor (one more driveable) and won't be turning those high rpms.

Do sidepipes just not want to flow above 6,000 rpms? Any thoughts/experiences on this?

Thanks.

B.

 

I wonder if it doesn't have something to do with the twin (nearly) 90 degree bends in each sidepipe. The under-car exhaust has a straighter, and therefore less obstructed, flow.

 

The results don't mean that much unless you run all the time without mufflers. Full length pipes and mufflers might be more restrictive than mufflers (not Hookers) that you can get for the sidepipes.

 

Anyone have a picture of the inserts he made?

 

Z-Man - No doubt muffler flow is an issue for me as well. I don't have it offhand, but I do have in my files a list of mufflers and what they flowed on a flow bench. With that number, you can figure out if it will be a restriction with your HP levels.

I hear what you are saying about the test above, but there just seems to be somewhat of a restriction way up top with the side mounts.

Although I do prefer the look of the Hooker sidemounts, I do wonder if the Stahl headers would have produced the same apparent disadvantage up higher in the RPM band?

B.

 

It could have something to do with the extra long primary tubes.

 

I thought that longer primary tubes produce more high rpm hp?

 

You may be right, but for some reason I always thought the opposite.

 

Longer tubes tend to give you a larger power curve, and increase torque over a larger range. The header diameter has more to do with where a header makes it's most power. For example think of a top fuel dragster, short large tube headers. They make all their power at high rpm and keep it there. Now if you wanted to build something for low end torque you run the longest tubes you can along with a fairly small diameter to keep exhaust velocity high.


Pat Kunz

 

 

The headers primary length will definetely move the power band. Longer tubes move the torque down, just as we're seeing in the graph. The side mount headers have longer tubes and so it makes more power down low, less up high. Text book.

 

I've read nothing but good about Stahls. I bet they are pretty good across the entire range, however, they are pretty pricey. Also, I tried to order some and received less than optimum customer service.

 

Excellent; thank you.

B.

 

Pat - Thank you for your insight as well.

Z-Man - Sorry to hear about the customer service on the front side. I do remember the Stahls being a bit on the high side as well. Do you recall the price range?

B.

 

Here is a picture. They were made with 2.5" ID smooth perforated tube with a difuser at the entrance. The sound absorber in the picture was fiberglass but it didn't last long. I am now using absorber material extracted from another glass pack muffler and that has held up well.

 

Just about a grand for the 1-7/8. I had aftermarket heads, so I needed stepped headers and the Stahl adapter flanges. Painted. Check out #115.

http://www.stahlheaders.com/Frame%20New%20Drag.htm

 

That would be one of my guesses.

I work in a research lab and we deal with this sort of thing all of the time. The number of bends absolutely does effect the flow potential in our systems. We go out of our way to eliminate bends in our tubing... our (orbital) welder cost $25,000... just to weld SS tubing (polished on the inside) and eliminate any ridges on the inside of the tube at the weld.

I don't know how much of this information translates for 2-1/2" car exhaust pipes, but I am willing to bet the number of bends is a factor.

 

those do look nice

 

will these work with Steeroids?

thanks,

jim

 

Don't know. I haven't seen anyone with that combination...