Sidewinder 'Dip'

[UK Luke 72]

Here's two three four examples.
Plenty of people have heard or seen the same around 3-3.5k rpm.

The 1 5/8" apparently top out around 170bhp, ties in with what VW speedshop say their system will support and the CB performance 170hp build. The 180bhp build steps up to 1 3/4"
I only gained a 3hp taking the muffler off, but we know my induction is limited in the upper RPMs until we swap to the 40s but we're not talking about the upper rpms here

Muffler or not, the 'dip' remained. So it seems header related. Right in that rpm we want all the torque.

Has anyone tuned around it?
What did it take?

My engine with the bigger cam in the first chart seems to recover quite well. Why would that be?

My 2276, FK10, 11:1 1 5/8" VW speedshop sidewinder
https://www.thesamba.com/vw/gallery/pix/2280739.jpg

Baz's 2276,JPM cam, 10.2:1 1 5/8" VW speedshop sidewinder
https://www.thesamba.com/vw/gallery/pix/2216496.jpg

2110, FK8, 9.8:1 1 5/8" sidewinder
https://www.thesamba.com/vw/gallery/pix/2076339.jpg

Tabari's 2276 V26 9.8:1 1 5/8" sidewinder
https://www.thesamba.com/vw/gallery/pix/1456904.jpg

Alstrups, 1914, web 163 A1 1 1/2" sidewinder
https://www.thesamba.com/vw/gallery/pix/1283700.jpg
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[modok]

Yeah I know.
Tho you take out the dip may also take out the peak below it.
And it can be mild or a problem, a lot to do with the head flow ratio.
Im a believer in 75 percent area ratio as well as flow

[Brian_e]

I don't have a dyno sheet with a dip, but I have put a bunch of miles on my bus with a sidewinder, and I get a 10-11.5 AFR dip right in that same rpm range. When it dips that low, you would guess it kills the power like the graph shows. I can certainly feel mine when it goes rich.

I have tried most everything to get rid of it. Swapping to a VSpeed is next to try. I have noticed it with 3 different engines with the same style sidewinder. All IDF's. I also know another guy with a similar setup, and his does the same thing.

Torben believes mine is related to my flange to muffler section being to short, But other guys have the same issue and different mufflers.

Just a thought on something kinda related. Do you have an AFR chart that goes with the dyno pull? Maybe it would show yours going rich and killing power at the same point?

Brian
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[74 Thing]

Here is a John Maher 2276 w FK10 with 44 IDFs 42x37.5 hand ported 044 heads and manifolds and came out with 179HP and 177ft lb of torque on the dyno. He used the CSP Python exhaust (which is similar to a sidewinder) in 42mm.

If you look at the graph there is a dip in the torque as well.
https://johnmaherracing.com/2013/02/1953_oval_179bhp/

Maybe you should try a different exhaust to try to get rid of the dip since you are going to hit the dyno again. http://www.ttexhausts.com/vw-beetle-exhaust/

Why do you think your hp/torque numbers are down a bit compared to others-throttle body size and heads and manifold flow and dyno differences?

[bugguy1967]

Using the AA 1 5/8" with no dip, but I believe the primaries to be too long, which should restrict power above 7,000 rpm.

The racers in Real Street that have tried, have removed their sidewinders--all of which ran faster after swapping to a traditional style header arrangement.
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"A petrol engine can start readily, run smoothly and give every appearance of being in good order, without necessarily being in good tune." - Colin Campbell, "The Sportscar Engine"

[UK Luke 72]

We only made one tweak in that area, but we were doing full power runs nust getting data for when we have bigger throttle bodies on. Everything after the dip was good in terms of AFR.
Yes it did go a little skewy which ties in with the dip, but the VE table scales linearly. Suggesting the exhaust just doesn't scavenge as well around those rpms?

I don't want an exhaust poking out the back, I know the full merged setups make more up top, but they don't quite tickle my pickle.

Tabari, the dyno chart I pulled of your engine shows the exact same dip we're talking about.


74, itb size. Hopefully I'll be into the 160 region soon with a minimised dip

Brian, the dip is still there with no muffler, we tested it on the dyno.
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[modok]

In a sense... longer duration makes up for longer tubes.
My tri-y does not stick out the back

My latest design could rule them all, in theory, but that's only in theory. LOT more testing needed, but I am confident that there is no need to have it sticking out the back in any case.

Would say more but I am caught off guard, 10-15 years ago I was FAR more into it and I've known about it for 20 years, better late than never.

HOW rich it goes should be an indication if its a problem or a feature.
That richness is double metering from reversion.
Good for MPG, but bad for heat. How can it be good for MPG? well not at WOT.
Secondary volume and length can be tuned to minimize it. IMO secondary length should be at least 2/3 primary length or same as primary length, and also will help to have more volume where it merges. Offroad systems which merge sharp are the worst for this.

[rayjay]

The other day I was looking at one of the cheapy old style bug headers with the super short collector and it got me wondering about "ideal" collector sizing and length. There's lots of good info on the net.

[Paul.H]

Well I do have a 1 3/4 inch merged "out the back" header that could be tested but I won't be fitting it that's for sure. Maybe you could all chuck in some cash and get Luke to do it ? Yeah thought not

It'd be like driving a reality train into "dysney world"

[94touring]

I have a rich spot (11s) according to my wideband in the same area on my 2110 bus, twin 40 idf's and just a c35 cam, 40x35 heads, with 1.5 inch exhaust. My solution was since I have a cb blackbox was increased the timing a couple degrees in the rich area and then pull it back out as air fuel goes back to mid-upper 12s.

[challomoner]

[94touring]

[Alstrup]

[challomoner]

Very informative post torben. Guess I'm going for the ballistic option then 😅

[modok]

A tri-y with secondaries 1/2 primary length, and tertiary 1/2 primary length
DOES work very well, and has no dips, but it's powerband is not very wide.
Compared to the dyno graphs here what you get is flipping the dip and the hump before it, just swaps them, so the powerband is "dip free" but actually narrower.
Although IMO that WORKS better for street driving and canyon carving. Killer midrange. Engine runs more consistent temperature. Good MPG when driving in the lower rpms.
But for street/strip it's not better. If you want to CRAWL on the street and fly at the track and/or when nobody is looking....not as good, because you are just using the top end and the bottom end, and will have live with some reversion in the midrange.
Lengthening the tertiary improves low end AND top end, but CREATES a dip in the middle.
Shortening the secondaries means you have to shorten the tertiary also so that's no overall improvement either, just narrower powerband.
So that "system" I think, "is what it is" and you can take it or leave it.
I've seen that kind of length ratio work well on MANY kinds of engines, and it works on VW and Porsche too.
But there are more possibilities.
The SAME way added volume near the merge can SOFTEN the problem in a four into one, SO can it with a tri-y.
The primaries can merge into the secondaries tight, but where the secondaries merge into the tertiary..... that is where volume could be added to allow the tertiary length to be longer and/or secondaries to be shorter and soften the bounce back from the other side.
I believe it CAN work and it hasn't been tried much.

Probably should learn how to tune your regular header too.
So, ready when you are. Get some tubing and lets get to welding.

[Alstrup]

Yeah, but oin the other hand, this 1 / ½ / ½ length is the part that I do not necessarily buy. I see the theory behind it, but real life sometimes differ from the theory. My reasoning is, that if you look at say a 1700 cc Kent engine I helped tune last fall, where we went from a 4-1 short tube header and a very annoying power and afr dip in the midrange to a hand built 4-2-1 header (The engine resides in a Westfield 7, so nothing fits and have to be hand built) The guy that built the header basicly copied a Burton 4-2-1 from a Fiesta XR2. Burtons super street/race header is 1 / 1,5 / 1. This engine pulls a healthy 145 hp @ 6300.
Also, both Simons and Supersprint 4/2-1 headers for Golf & Jetta´s are 1 / 2 / 0,5, or their high rpm ones which are 1 / 1,5 / 0,5
Manufacturers for Honda tend to use 1 / 1 / 0,5 for street engines and a lkittle shorter secondaries for higher rpm track engines.
Opel is basicly the same pattern.
I had the opportunity to help work on a Mercedes 230 SLK which had a Klemann power kit installed (It went bad because they over did it as Klemann often do, so it needed a rebuild.) This engine has an M62 supercharger, so it is not 100% apples to apples, BUT, I did notice that the Supersprint header on it also was 1 / 1 / 0,5. This engine was 235 hp/350 Nm after the detune.

All this taken into consideration, with most of these engines designed to peak at or above 6000 rpm I have the feeling that the secondaries should be longer if possible.
Also, when the Slk 230 was repaired I came across a calculator specificly developed for designing 4-2-1´s for Mercedes. We played a little with it both with low and high boost to see how it affected the exhaust lengths and in all cases it recommended secondaries in the 3/4 to 1 compared to the primaries.

As always, we will have some space limitations, but based on these observations I tend to lean in the direction of relatively longer secondaries in order to make the engine have a wider powerband. But I am open to be proved wrong
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[Wreck]

Does changing the intake length make any difference to where the dip is and how bad it is ?

[UK Luke 72]

[94touring]

[Alstrup]