Highest power exhaust for GSX-R750 L1 2011-2023?

[BLSTIC]

Duplicate post

[ptuomov]

According to the simulation, the resonator can hurts a little bit in the 7500-11000 rpm range and does about nothing to the top end:

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Black with a can, green with straight pipe.

The can in question pictured here:

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[BLSTIC]

Is that the correct way to model it? I saw engmod4t has a ton of different ways to model muffler-ish things if proper wave action was required to be simulated.

[ptuomov]

Is that the correct way to model it? I saw engmod4t has a ton of different ways to model muffler-ish things if proper wave action was required to be simulated.

It's an empty resonator can with a perforated tube. I modeled the main muffler using the full muffler functionality, but just modeled this as an empty can without the perforated tube. It's not right, but it's close enough to government work -- in my opinion, it gets the direction correct.

[ptuomov]

We’ve got three fully rebuilt and fully legal engines now in addition to the existing one in the car. With the second (identical to the current) exhaust bunged for individual cylinder fuel tune, each engine should last a very large number of track miles with all cylinders at right AFR at all rpms. Our focus will soon move from the powertrain to handling, starts, weight distribution, etc.

[ptuomov]

Getting ready to shake down and test on ice:

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[ptuomov]

I know this is the wrong forum, but any thoughts on the chassis setup?

On paved track and long races with regular (rear differential) race cars, my rule of thumb is that you want the center of gravity as low as possible and about 60% weight in the rear and 40% in the front. With the appropriate suspension, center of gravity below the wheel hub center is money.

This car has a live rear axle without a differential (so the inside wheel must lose traction in corners), is driven on a circuit that is 1/2 gravel and dirt and 1/2 paved. Furthermore, the races are very short (3-5 laps with 1km lap) with a standing start so it's about 1/2 a drag race at the start and 1/2 a circuit race afterwards. Clockwise track but a lot of turns in both directions. Where would one want the center of gravity for a car like this?

[BLSTIC]

Just throwing it out there (haven't looked into chassis setup much beyond the things you normally have adjustment for) but it sounds to me like you want decent weight transfer then, not just front to rear for the drag race, but left to right as well so you don't have the axle fighting so hard to go straight, at least on initial turn in.

The problem with high weight transfer is that it it tends to oversteer under acceleration in turns from the difference in traction/normal force.

Perhaps you could do it with springs and bar? A stiff rear anti-roll bar would lift the rear on turn in, and if you had (very aggressive) progressive springs on the front (soft linear on the back) you could get at least some diagonal weight transfer back on the wheel once you're already sideways.

I almost certainly introduced unintended consequences in this post though.

Come to think of it, is a rising rate anti-roll bar a thing? I can think of a way to make one but I've never heard of one

[Rick!]

See my response in your Chassis post.

[ptuomov]

The problem with high weight transfer is that it it tends to oversteer under acceleration in turns from the difference in traction/normal force.

This is an additional good point which I have to think thru. If you're already accelerating when the still turning, you're using some of the rear wheel traction budget to turn and some to accelerate, which should cause understeer. Countering this, I believe that the weight transfer helps the rear wheel traction and hurts the front wheel traction because the weight transfer due to forward acceleration doesn't by my understanding impact the centripetal force working on the center of gravity.

I have to talk to the driver and he'll educate me on whether this is an issue.

[ptuomov]

See my response in your Chassis post.

Didn't see it there.

[BLSTIC]

The problem with high weight transfer is that it it tends to oversteer under acceleration in turns from the difference in traction/normal force.

This is an additional good point which I have to think thru. If you're already accelerating when the still turning, you're using some of the rear wheel traction budget to turn and some to accelerate, which should cause understeer. Countering this, I believe that the weight transfer helps the rear wheel traction and hurts the front wheel traction because the weight transfer due to forward acceleration doesn't by my understanding impact the centripetal force working on the center of gravity.

I have to talk to the driver and he'll educate me on whether this is an issue.

I was more referring to when a rwd car is turning left in oversteer under power (ie dirt track most of the time), more "weight" (spring load, corner weight, weight transfer, whatever) on the right hand wheel induces oversteer/rotation under power from the right wheel having more available traction from the higher normal force.

If you counter this by increasing the right *front* spring rate, preload, ride height (or even front bar) you get diagonal weight transfer and more pressure on the left rear, and the car tends to rotate less under acceleration.

I used to do what I could to get the car to understeer on power. I never reached that point, I didn't have that car for very long, but the reduction in oversteer meant that I could apply what little power I had much earlier in the corner than on the initial shakedown runs.

The problem is getting the diagonal weight transfer on the exit of the corner while still allowing the car to do the initial turn-in

[ptuomov]

What kind of individual cylinder fuel trim maps do you guys use with equal-length intake trumpets and sequential tri-y motorcycle exhaust?

[ptuomov]

A general observation from running a bunch of EngMod4t simulations: The individual cylinder trim is influenced both by unequal intake trumpet lengths and non-symmetric exhaust design. The exhaust configuration matters much more at low rpms and the intake configuration much more at high rpms. For an engine with 15k redline rpm and 11.5k peak torque rpm, below 8k rpm the individual cylinder trims are all about asymmetric exhaust pulse interference and above 8k rpm they are all about intake trumpet lengths. I am thinking that this might not be specific just to this engine but might apply more generally to four-cylinder engines that have varying intake and exhaust geometry across cylinders.

[modok]

Indeed,that is probably true more often than not. It's even possible an exhaust system that should be symmetrical will run like it isn't.
I don't think you will have to worry about that, but, it happens a lot more than people think.