Zoomies vs collector headers

[noslin]

Jim Fueling (rip) came up with those anti-reversion cones/headers back in the late70's, if they worked, they would still be used today you think?
 Again, long runs at a constant rpm could show some improvment (B'ville) but for the short duration of a drag race and that the classes that allow collectors are index/bracket---whats the point??

whats wrong with having a discussion about this (or anything else) even if your bracket/index racing?  The OP did not say anything about bracket/index racing.  its just a discussion between the two.

[Roger]

That's OK noslin. Look at all the great discussion this generated. Everyone has different opinions and that's cool. I'm going to go back through all this and see if I can learn something from it.

[Paul New]

When we ran our car injected alky with a mild SBC we switched from collector headers and lost a tenth and was never able to get it back with the zoomies..... we switched because zoomies look cool but HP was not the same. Later we ran at an event that required mufflers car went quicker again with the collector headers, even with this we went back to zoomies and sold the collector headers and put a blower on the car!!

[Roger]

Here’s some of the little published info I could find on the subject:

ZOOMIES vs HEADERS
Stahl Headers Newsletter, Issue #4, March, 1988
“It appears that most current late model dirt engines are 406’s to 430’s. Zoomie pipes (8 individual exhaust stacks) will run quite well from 3500 to 4500 and from 7000 to 7500. But, they give up from 25 to 35 HP at 5500 to 6500 which ends up being on the chutes where you can use all the power you can make. However, compared to Zoomies the “Shorties”, as we have labeled that collection of pipes that vary in pipe length from 14” to 16”, are the real disaster. Reports from several prominent dirt late model engine builders indicate as much as 45 to 50 HP difference between 5500 and 6500.”

With this input in mind my little 325hp street engine that goes in the roadster first will never see the high side of 5700rpm and might see little if any loss of performance between headers and zoomies. Maybe run quicker with zoomies because the headers added weight! So, I’m going to run both on my car and see for myself. Then when the race engine is done I’ll do the same thing again with zoomies and a set of larger headers that I’ll beg, borrow, or temporarily appropriate. From all the actual experiences that’s been shared here I’ll have a good chance of being a tenth slower with the zoomies. I’ll find out.

The Denverflatheader posted what I thought was a really good article that starts to look at cam timing that could help get back some of the power that was lost without headers. After talking with 4 different cam companies (who all had a little different idea of what was needed) they all pointed to a cam that needed more exhaust duration, an increased lobe separation angle, and minimum overlap as compared to a similar cam used with headers. Jones Cam Designs told me they did some tests years ago using zoomies and were emphatic that the exhaust side of the cam needed 10 degrees more duration than the intake.

And I found this little piece of information:

“I have found a consistent 5-8% power increase if the primary pipes are kept separate (zoomies), with a megaphone fitted to each primary”. This was written by A. Graham Bell, a noted engine tuner and tester in England about the same time David Vizard was also running similar testing in England. Megaphones on the end of your zoomies? Not a chance with me:)

Thanks to everyone for all their input. After all, a little shared knowledge can go a long ways in helping everyone better understand the technical parts of our sport. And that’s the point.

[denverflatheader]

Roger – am a strong advocate of empirical testing too, like your “plan to do” for your roadster.  Calculations and what-if scenarios are excellent today with computers, so easy, but the answers are hard to recall with passing of time.  First-hand testing, you remember forever.  Alan

dusterdave173 – good one on determining torque tube/collector length without a pyrometer.  Read that and saw immediately the benefit with your idea, and has a built-in correction factor (e.g. 4.00 versus 5.00 inch diameter).  You have to start somewhere… Alan

[wideopen231]

If anythinhg I hope that 5500 to 6500 is only place you loose.My combo is setup to leave at 6800 and shift at 7600 and cross finishline around 8800 to 9000.I can see zoomies loosing out on bottomend and have no problem with that.

[noslin]

  After talking with 4 different cam companies (who all had a little different idea of what was needed) they all pointed to a cam that needed more exhaust duration, an increased lobe separation angle, and minimum overlap as compared to a similar cam used with headers. Jones Cam Designs told me they did some tests years ago using zoomies and were emphatic that the exhaust side of the cam needed 10 degrees more duration than the intake.

 

one thing ive learned from hangin with my buddy who is the gearhead when it comes to engines.  he is a n20 guy, from what i understand the n20 guys move the exhaust lobe depending on how much hp they plan on making.  i think technically, they add the duration for the added exhaust from the n20 but then have to move the lobe to get the overlap back where they want it.   so, maybe in the sense of what the cam gurus are trying to do is help the scavenging of the exhaust by haning it open longer and also as the n20 cam guys do, move the lobe to get the overlap where it needs to be. i dont know if this is correct thinking but its something to discuss.

i wonder if its really fair test if just changing the headers and not changing the cam.  if setup is designed for collector style header setup and put zoomies on or visa versa, is it really an accurate assessment if one makes less/more hp then the other.

[dreracecar]

Exactly,  If only we could build our motors from the Jegs or Summit catalog based on advertised HP gains listed with the parts, one could build a single carb 350 Chevy that made 1200 HP for $2500

[noslin]

Exactly,  If only we could build our motors from the Jegs or Summit catalog based on advertised HP gains listed with the parts, one could build a single carb 350 Chevy that made 1200 HP for $2500

you sure your on the right thread?

[Roger]

My view of how to maximize power output with zoomies falls in line with what wideopen231 & noslin have said. If Stahl’s concept that you lose power between 5500-6500rpm is correct, then have a convertor that flash stalls to at least 6,000rpm to minimize the hole in the power curve might be a wise move just as wideopen231 mentioned.

As far as noslin’s thoughts, they might be right on the money. If you don’t have the effect of a collector headers to help evacuate the cylinder then you have to do something like opening the exhaust valve longer to do a better job of clearing the cylinder of burned gases. And to keep exhaust reversion, that’s exhaust flowing into the intake, to a minimum then add a few degrees of lobe separation in order to reduce the amount of overlap time for the reversion to occur. That’s the way it was explained to me by some very experienced (didn’t want to call them old!) and well known cam designers. Of course, this has little if anything to do with supercharged engines. But they weren’t the focus of my original question, I probably should have made that more clear.

As far as changing a cam and headers, the best I can do is use the same cam designed for zoomies with more exhaust duration and a wider lobe center angle and then put the headers on and see what happens. But it’s a good point.

Picked my updated car up from the chassis shop today so here’s a quick photo. Will post more in the Altered section after I get back from a short leave.

[BK]

“I have found a consistent 5-8% power increase if the primary pipes are kept separate (zoomies), with a megaphone fitted to each primary”. This was written by A. Graham Bell, a noted engine tuner and tester in England about the same time David Vizard was also running similar testing in England. Megaphones on the end of your zoomies? Not a chance with me:)

Maybe not  Megaphones. But what about stepped Zoomies?

[coupemerc]

Good discussion but don't loose sight of the big picture which is "the car". For example, I'm attempting to race in B/ND. Collector headers are prohibited, car is very light and I'm limited to a 12" wide tire. I don't know that I would want a ton of low end torque.

[noslin]

Maybe not  Megaphones. But what about stepped Zoomies?

in reading a bit, it sounds like the larger the exhaust opening (end) the stronger the negative pressure wave will be.  maybe this is why the megaphone is better then single diameter tube. 

maybe with the stepped zoomie there might be some benefit to this if calculated out correctly for each step.   i wondered about a reducing step and what effect that would have on the negative pressure wave if any.   sticking with conventional enlarging stepped headers, depending on where the step is, could tune it for the 5500-6500 range and probably wouldn't look bad either.

on my vw we went with stepped on third order.  total length was bout 36" long.  first two at 13" and then single about 13"   the turbo had divided housing and to effectively keep pulses equal for each side paired up opposing firing cylinders (1432 order) 1/3 2/4.  it would spool 30lbs in about .6 seconds on 70mm wheel for 140 cubes. 


dean

[Roger]

Update on collector headers vs. zoomies.
Took my roadster to the local 1/8 mile track yesterday and tested headers & zoomies. In an earlier post on this thread I took a guess that in certain low horse power circumstances, both exhaust systems would create similar if not close to the same results. This will be the first of two or three tests with future engine combinations, God willing:) The engine used in this first test is a Chevy 350 street machine engine that produces about 260hp in the car, idles at 700rpm, and pulls 14” of vacuum at idle. The cam has 1 degree of overlap at 0.050” lift while the compression ratio is 8.3-1 with the stock 86,000 mile dished pistons, cylinder walls, and stock heads.

 The car is foot braked and uses a 2100rpm stall convertor along with 4:10 gears and 31 tall slicks. Since the power band of this engine is relative low compared to an all-out race engine, it’s shifted at 5300rpm and goes through the traps at 4450rpm. While it would probably go quicker if I shifted it at a higher rpm, the Stahl Headers Newsletter comments earlier in the thread that zoomies have little effect at lower rpms compared to collector headers was the reason for this test. My header tubes have a 1 5/8” dia, are roughly 39” long, and have a 3” collector. Just about right for this engine’s rpm operating range. The zoomies are 10” long and have a 1 ¾” dia. The zoomies weigh 10# per pair while the headers weigh 24#.

The first 2 runs were with headers and the air temperature was 80 degrees. The last 3 runs were with zoomies and the temperature was 85-90-85 degrees. Everything else about the car stayed the same.

1st run with headers:   7.008et at 100.45mph
2nd run with headers:   6.975et at 100.22mph
3rd run with zoomies:   6.924et at 101.58mph
4th run with zoomies:   7.014et at 100.22mph
5th run with zoomies:   6.985et at 101.12mph

Average with the headers is a 6.991 at 100.33mph, and with zoomies is a 6.980 at 100.97mph. That’s an average difference of only 0.011 elapsed time between the two and a difference of 0.64 miles per hour, with the zoomies having a tiny advantage. If you apply these numbers to a performance calculator the headers make 254hp at 1620# race weight while the zoomies make 257hp at 1606# race weight My take-away from this test is that it makes little, if any, difference between the two types of exhausts if you operate at less than 5300rpm and your cam has little or no overlap. The lack of overlap will negate some of the wave scavenging effect of the headers. And the zoomies are staying on this engine as long as it’s in the car. When the race engine is done, we’ll do this all again with larger & shorter collector headers along with the same zoomies. Testing ideas start somewhere and this first one is the ground floor. The car may be slow right now but I’m supporting my local race track and enjoying life!

[denverflatheader]

Roger - enjoyed seeing initial results, your tests very accurate confirmation of the Stahl Newsletter.  Alan