Header primary diameter for a small motorcycle engine

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Rick!
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Re: Header primary diameter for a small motorcycle engine

Post by Rick! »

ptuomov wrote: Fri Jul 30, 2021 1:18 am Here’s what the curve looks like with the latest prototype exhaust, as of yesterday. Any obvious things to do if I want to shift the torque curve even more to the left? Just the usual, that is, smaller diameter longer pipes?
Help us understand the difference between the left and right graphs. The left graph is from the original post on 13,000rpm to 9300rpm where it looks like there is NFW that combo was ever going to hit 90hp @9300 (relative number). Or is the RH graph from a competitor's dyno run and that's your target?
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You can get a spare set of cams and let Camking do his thing. You've already been dq'd for some piddly detail, make them work for it this time.

For those looking for rules information, here is the 2016 version. I'm still not clear on how the RPM is limited to 9300.
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Re: Header primary diameter for a small motorcycle engine

Post by ptuomov »

The last figure that goes to 15k rpm is from yesterday with our prototype exhausts. I don’t have a comparable stock exhaust graph for you to post, but the prototype was better across the board compared to both the bike exhaust and the most popular exhaust with these cars. Surprisingly, even at the top end, despite the much smaller primaries.

I’m going to blank out the hp numbers on the y axis from future posts because that’ll help us focus on the shape of the curve.

Given the shape of the last dyno run curve, is there an obvious change we should make to the exhaust? If one can’t conclude anything from it, that’s fine. However, my thoughts are that since the torque curve stays so flat up to 13000 rpm, this suggests that for a 9300 rpm limited engine we should make the pipes all significantly smaller diameter. Significantly smaller than the current “smallest that anyone has ever run” size that we tried yesterday.
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Re: Header primary diameter for a small motorcycle engine

Post by ptuomov »

Rick! wrote: Fri Jul 30, 2021 7:59 amI'm still not clear on how the RPM is limited to 9300.
There's a locked ECU box that you must buy to race in this rpm-limited series. It cuts fuel at 9300 rpm and above.

The ECU box has the same external interfaces as the unrestricted rpm ECU box, so one can just swap the boxes and run the full rpm range.

Fuel maps can be independently adjusted with Power Commander within the rules in both the rpm restricted and rpm unrestricted classes.
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Re: Header primary diameter for a small motorcycle engine

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However, my thoughts are that since the torque curve stays so flat up to 13000 rpm, this suggests that for a 9300 rpm limited engine we should make the pipes all significantly smaller diameter. Significantly smaller than the current “smallest that anyone has ever run” size that we tried yesterday.
May I ask, What is this “smallest that anyone has ever run” diameter size?

Thanks.
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Re: Header primary diameter for a small motorcycle engine

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Ptuomov, given Exhausted's strong preference for large radius bends such as 4" for 1 3/8" od 0.060" wall, have you succeeded in sourcing similar sizes or are you persevering with ~3" radius?

Has anyone succeeded in sourcing smaller od pre bend in large radius 304L, 316, or 439, none of which suffer from the embrittlement plaguing 304 - - 321 being too expensive for this hobbyist

I've tried Performance Tube, Columbia River, Patriot Exhaust, Cone Engineering, SPD, Burns Stainless etc and none stock 1 3/8" or 1 1/2" od 0.060" wall pipe at 3" radius - - some list it, but a phone call reveals "no stock"

I'm even willing to use std 1018 mild steel pre bend then ceramic coat it, but that's also unavailable
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Re: Header primary diameter for a small motorcycle engine

Post by ptuomov »

Leftcoaster wrote: Tue Aug 03, 2021 1:41 am Ptuomov, given Exhausted's strong preference for large radius bends such as 4" for 1 3/8" od 0.060" wall, have you succeeded in sourcing similar sizes or are you persevering with ~3" radius?

Has anyone succeeded in sourcing smaller od pre bend in large radius 304L, 316, or 439, none of which suffer from the embrittlement plaguing 304 - - 321 being too expensive for this hobbyist

I've tried Performance Tube, Columbia River, Patriot Exhaust, Cone Engineering, SPD, Burns Stainless etc and none stock 1 3/8" or 1 1/2" od 0.060" wall pipe at 3" radius - - some list it, but a phone call reveals "no stock"

I'm even willing to use std 1018 mild steel pre bend then ceramic coat it, but that's also unavailable
For the summer, I’m working with metric sizes and mild steel. My buddy has a pipe bender setup at work so we get whatever we want from straight pipe.
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Re: Header primary diameter for a small motorcycle engine

Post by Leftcoaster »

ptuomov wrote: Tue Aug 03, 2021 2:39 am
Leftcoaster wrote: Tue Aug 03, 2021 1:41 am Ptuomov, given Exhausted's strong preference for large radius bends such as 4" for 1 3/8" od 0.060" wall, have you succeeded in sourcing similar sizes or are you persevering with ~3" radius?

Has anyone succeeded in sourcing smaller od pre bend in large radius 304L, 316, or 439, none of which suffer from the embrittlement plaguing 304 - - 321 being too expensive for this hobbyist

I've tried Performance Tube, Columbia River, Patriot Exhaust, Cone Engineering, SPD, Burns Stainless etc and none stock 1 3/8" or 1 1/2" od 0.060" wall pipe at 3" radius - - some list it, but a phone call reveals "no stock"

I'm even willing to use std 1018 mild steel pre bend then ceramic coat it, but that's also unavailable
For the summer, I’m working with metric sizes and mild steel. My buddy has a pipe bender setup at work so we get whatever we want from straight pipe.
Congratulations, using metric sizing yet - - not only are 4" radius bends impossible to find in 1 3/8" and 1 1/2" o.d.'s but when "stepped" there's an undesirable 19% increase in area - - if increasing to 2.0" od by 1/8" increments the area difference decreases by 17, 16, 15, and 14%; where possible a 15% area reduction being preferred at each step

Starting at 1 5/16"od and increasing to 1 3/4" with 1/16" increments, it seems metric equivalents are 32, 35, 38, 40, 42, and 45mm ods, which if they can be "slipped" into one another and depending on wall thickness, can create area differences closer to 15%

Are you able to share the diameters, wall thickness, and radius' you're working with - - and whether your colleague may be willing to supply other customers?

I reached out to Brazilian and Argentine manufacturers, but it appears their aftermarket relies on inch sizes created by imported US dies
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Re: Header primary diameter for a small motorcycle engine

Post by englertracing »

Once you go smaller hide your findings inside some big diameter dummy primaries to confuse the competition :mrgreen:
To keep it light you want 0.8 or 1mm wall
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Re: Header primary diameter for a small motorcycle engine

Post by ptuomov »

The material selection is totally beg borrow and steal here now, so we’ve got short sections of 2mm wall tube (!), Lada Samara aftermarket primaries (!!), home made collectors, etc. in this exhaust. It’s a Frankenstein with all sorts of DNA in it, but it does want to go pretty hard for a four stroke exhaust. I doubt that anyone would copy it because of the looks alone, no matter what the results! It is however not necessary to further camouflage it as the external diameters don’t appear to have any rhyme or reason to them. Exporting these materials might amount to unintentional comedy and the recipient suspecting a candid camera episode being filmed.
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Re: Header primary diameter for a small motorcycle engine

Post by Momus »

Slow taper primaries (or stepped) from laser cut, light guage 304 ss, might be a feasible hydroform option if ugliness is tolerable or desirable.
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Re: Header primary diameter for a small motorcycle engine

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Momus wrote: Sat Aug 07, 2021 8:54 am Slow taper primaries (or stepped) from laser cut, light guage 304 ss, might be a feasible hydroform option if ugliness is tolerable or desirable.
The pipes currently in the car being raced this weekend have steps both in the primary and secondary pipes. I like steps.

If I attempt to hydroform anything in a concrete mold with pressurized water, it's for sure going to be ugly!
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Re: Header primary diameter for a small motorcycle engine

Post by ptuomov »

I just saw a video of a 600cc engine in this series making 96+ crank hp at 8800 rpm with long and skinny AF 4-2-1 headers and secret sauce intake trumpets. Their headers look like instagram models compared to our regular housewives. We're making low to high sixties hp in the rear wheel on a calibrated dyno depending on things, so on the dyno we suck relatively to the competition and likely suck absolutely too. The two cars did a bit of an unofficial drag race today and the 96+ hp competition left us in the dust. So it's not just their happy dyno, they burn rubber on low gear shifts and we have a great viewing angle on their rear wheels! Their driver driving our car said that our car must have a lot longer gears while in reality we are within the rules mandated +/-1%.

Then again, our driver can turn the wheel and press the pedals. I think he was among the fastest in the free practice with the underpowered car tonight.
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Re: Header primary diameter for a small motorcycle engine

Post by Momus »

ptuomov wrote: Fri Aug 13, 2021 2:50 pm
Momus wrote: Sat Aug 07, 2021 8:54 am Slow taper primaries (or stepped) from laser cut, light guage 304 ss, might be a feasible hydroform option if ugliness is tolerable or desirable.
The pipes currently in the car being raced this weekend have steps both in the primary and secondary pipes. I like steps.

If I attempt to hydroform anything in a concrete mold with pressurized water, it's for sure going to be ugly!
No need at all for a mold.

2 stroke expansion chambers are regularly formed from 2 flat profiles with lightly flanged edges welded and pressurised.
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Re: Header primary diameter for a small motorcycle engine

Post by MadBill »

Momus wrote: Mon Aug 23, 2021 2:49 am.
2 stroke expansion chambers are regularly formed from 2 flat profiles with lightly flanged edges welded and pressurised*.
*With water of course, never air.
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Re: Header primary diameter for a small motorcycle engine

Post by BLSTIC »

MadBill wrote: Mon Aug 23, 2021 12:16 pm
Momus wrote: Mon Aug 23, 2021 2:49 am.
2 stroke expansion chambers are regularly formed from 2 flat profiles with lightly flanged edges welded and pressurised*.
*With water of course, never air.
But I like the risk of death...

Also, home water blasters can probably provide appropriate pressure for this. Air compressors - not so much.
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