13100 rpm fourbanger restricted to 9300 redline

[ptuomov]

Run CR9EK plugs, give you a little bump in compression, we sometimes deepen the pocket to push the plug down further.
Get a manual cam chain tensioner, its good insurance.
Grind down the cam chain plastic guide a bit between the cams, it creates some drag on the chain. Line bore the cam tunnels, Suzuki is terrible.
No other tricks, you can take a lick off the deck of the block if its passes inspection, 0.025" PTH and it will sing.

Repairs according to the manual are legal, so I have to see what the manual says one should do with a slightly corroded or scratched block.

[johnef]

Keeping stock gasket, and put PTH to 0.025" by machining the block down to get your desired PTH. She will hum.

[ptuomov]

Keeping stock gasket, and put PTH to 0.025" by machining the block down to get your desired PTH. She will hum.

And the head will also work better that way, compared to shaving the head.

How much will the camshafts retard if I shave the block that way?

[stealth]

Splash of Nitro in the tank...

[ptuomov]

Splash of Nitro in the tank...

That would smell, no? They do take fuel samples. I think one could theoretically create a swirl pot sort of fuel reservoir in line between the in-tank pump and the injectors and use that to spike only the fuel that is used in the startup. But since the cars take a variable time to line up with engines running, it would have to be a pretty big one. In any case, this is just for shits and giggles hypotheticals, we're not going to run with illegal fuel.

In any case, we now have two chassis/cars, one of which gives 10% less power to the wheels. Everything else has been swapped between the cars except the frame, the rear axle, and the wiring loom. Swap the ECU, swap the throttle bodies, swap the power commander, swap the exhaust, swap the air box with sensors, swap the whole engine, etc. the chassis number 1 always dynoes 10% higher across the entire relevant rpm range than supposedly identical chassis number 2. Both on a tire roller dyno and a hub dyno. Any ideas?

[BLSTIC]

I'd be looking at the rear axle then, and any bearings supporting it. If it's mounted like a go kart and the bearings that support the axle aren't designed to operate at an angle anything bent will stress the bearings a lot.

Also if it still uses a chain drive, there's a lot to say about efficiency there. A worn, poorly lubed, or otherwise wrong chain system on a bicycle can chew up to 10%. There's even a measurable difference in cyclist performance between most common practice and best technology.

Have you confirmed that you are getting the same signals at the ecu connector, and checked resistance on each wire?

[ptuomov]

On a dyno, both chassis coast down with same resistance. The computed driveline loss from the roller dyno is the same.

All the bearings in the rear of the car have been replaced already…

[MadBill]

"...and the wiring loom..."

Possibly low ignition primary voltage due to a bad connector, ground or partially severed wire? Or, real longshot, battery and alternator.

[Momus]

Splash of Nitro in the tank...

That would smell, no? They do take fuel samples. I think one could theoretically create a swirl pot sort of fuel reservoir in line between the in-tank pump and the injectors and use that to spike only the fuel that is used in the startup. But since the cars take a variable time to line up with engines running, it would have to be a pretty big one. In any case, this is just for shits and giggles hypotheticals, we're not going to run with illegal fuel.

In any case, we now have two chassis/cars, one of which gives 10% less power to the wheels. Everything else has been swapped between the cars except the frame, the rear axle, and the wiring loom. Swap the ECU, swap the throttle bodies, swap the power commander, swap the exhaust, swap the air box with sensors, swap the whole engine, etc. the chassis number 1 always dynoes 10% higher across the entire relevant rpm range than supposedly identical chassis number 2. Both on a tire roller dyno and a hub dyno. Any ideas?

What are the details of the rear axle- photos?

I've done a bit of work with low friction, low rolling resistance drives.

[ptuomov]

"...and the wiring loom..."

Possibly low ignition primary voltage due to a bad connector, ground or partially severed wire? Or, real longshot, battery and alternator.

I can think of three ways that the ECU can impact the power that the engine produces:
(1) Secondary electronic throttles
(2) Quantity of fuel injected
(3) Ignition advance

We have verified that (1) and (2) are the same between the cars. (1) can be verified visually and (2) can be verified with a lambda meter. There's no chance that either explains 10% torque difference throughout the curve.

We just ordered a device that allows us to see the ignition advance. If that is different, then ECU inputs are to blame. Wiring loom, sensors, etc. It's not the ECU as swapping the ECU between cars doesn't change the situation.

If the ignition advance is the same, then the power has to be lost between the transmission output sprocket and the tire.

Right?

[ptuomov]

What are the details of the rear axle- photos?

I've done a bit of work with low friction, low rolling resistance drives.

https://www.speed-car.com/xtrm-e.html

Same manufacturer, different model year karts, so not fundamentally different.

[Rick!]

Short center distances between sprockets are much more sensitive to slight misalignment than longer ones, like on a motorcycle.
You may want to look up some chain/sprocket formulas just to verify the center distance and chain length is proper for your sprocket combination.
Tight chains are not fast and will eat power and wear our sprockets faster.
The primary drive sprocket looks hella small which will exacerbate center distance and alignment issues.
O-ring chain or cheaper version? What is the smallest chain that will work for your hp level? Beefy chains eat power also.

The pic doesn't show how the center section is attached to the frame. There is more than just two thin walled brackets, right?
Is the center section square to the chassis? Is the engine square to the chassis and the center section? Most engines like that use shims for horizontal adjustment. The center section should have room for shims if done right.
The chain adjuster is just on one side? How do you keep the center section straight when tensioning the chain?

Did you do the wholesale swap and put the "low power" engine into the "hi power" chassis?
Same with tires, sprockets, axles and center sections - what does it take to make the hi-power chassis lose 10% power to the wheels?

Maybe keep track of your changes with a proper fishbone diagram and notebook to eliminate memory lapses and "I thought we already did that" issues.

[ptuomov]

Did you do the wholesale swap and put the "low power" engine into the "hi power" chassis?

Same with tires, sprockets, axles and center sections - what does it take to make the hi-power chassis lose 10% power to the wheels?

Maybe keep track of your changes with a proper fishbone diagram and notebook to eliminate memory lapses and "I thought we already did that" issues.

Yes, we did a wholesale swap of the bike engines (and transmissions) between the two chassis. ECUs also. However, what has not yet come off the two chassis is (a) wiring loom and (b) anything downstream of the motorcycle engine front chain sprocket. Because of this, the 10% additional torque loss in one chassis has to either come from ECU input problem thru the wiring loom (which would have to manifest itself in an ignition issue because fueling is the same per lambda sensor and electronic throttles can be visually confirmed to open the same amount) or a mechanical problem downstream of the front chain sprocket. Right?

The same difference shows up with a hub dyno and tire roller dyno so it can’t be the tires. But it could theoretically be anything in the rear axle and chain geometry, even though two two chassis are manufactured by the same manufacturer and we’ve swapped all items that usually wear (sprockets, chains, bearings, etc.) in both chassis.

[ijames]

Trying to approach this from a different direction, this may not be useful. Either the engines are actually making 10% different power, or the power is being made but is being lost in one of them. Start with #1. You say the AFR is the same so the fueling is the same, but do you have any way to measure actual engine airflow or fuel flow? Can you log the ecu data and compare the engines that way? If somehow the airflow is restricted on the weak chassis you would see the same afr on the lambda meter if the ecu tune is good but different maf or map or ve (or whatever your ecu reports) readings. As for #2, these are making about 70 hp (I think you said), so 10% is 7 hp. If you are making the power but it isn't getting to the wheels it must be getting lost due to friction and should show up as heat. I would think that 7 hp (= 5225 watts) worth of heat should show up with an IR thermometer somewhere after a bit of time under load. Make a run on the dyno or a lap or whatever, then take readings on the engine, chain, sprockets, cv joints, rear end, all the brakes, everything you can. One of those cheap ir cameras would be great, or try to video the display on a simple ir thermometer while also showing where the laser dot is aimed and just slowly scan it over everything as soon as you shut down the motor, then do the other car the same way.

Good hunting.

[Momus]

There are a lot of places in that rear drive you could be losing power due to friction and misalignment.

First thing to check would be your toe alignment.

Too tight press fits of ball bearings in the hubs or fit of the wheel spindles in the bearings is easy to over look and will cause zero or negative clearance.

Drive unit misalignment

Friction seals LU/ LLU type, may be fitted instead of no contact LB/LBB type or Z/ZZ shields if balls.

Tight CV joint ball tracks, bottoming CV

Correct bearings but crush preload on the upright bearings from innacurate assembly, ditto for the sprocket carrier assembly

Brake drag from misalignment, master cylinder adjustment sticky pistons etc.
Slight pitching error on the sprocket teeth is not unknown. Unnecessary O ring chain.

Chain run looks strange on the underside?