I had my 1500cc engine rebuilt by SM this summer, and local dealer installed it. I just had it out at Cota for the first HPDE outing. A few things are different from the original ~42 hours before my first rebuild.
- The gearing seems different. For example, on the main straight at Cota I just barely get into 6th gear now after the rebuild, but I used to get into it much earlier. I have not reviewed data yet, but am running same best track times as before so I would expect corner exit speeds to be similar. Would the SM engine rebuild to the new "X" engine designation with improved clutch bearing have changed anything with regard to transmission ratios from the original 2021 SR3XX?
- The install after rebuild also included a new throttle cable and new throttle position sensor. But, now car has difficult time idling, seems too low. I need to look into adjusting idle up slightly.
- My GDU was completely gone thru and inspected, supposedly looked brand new and was resealed.
- More concerning is a very unusual shift issue has arisen for the first time. It occurred 2-4 times in three sessions. After downshifting for approaching corner, and rapidly accelerating from the corner, the engine or transmission is slipping (almost like downshifting momentarily) or hiccup, hard to explain. This primarily happening between 2nd to 3rd, but once or twice from 3rd to 4th, no other gears. This is concerning as quite abrupt acceleration ~1 second stall. Any ideas? Could it be some type of clutch adjustment (I have standard, not spin safe).
Thanks, Dan
Hi Dan (@raider89), several people have reached out to me with this exact same question about the x engine conversion. One had a brand new car with an x engine that exhibited the same characteristics that you described. I haven’t reached out to any of the experts to ask but I understand that the gearing is the same so I am wondering if the difference in performance is caused by the change from 50w oil to 60w oil that Radicals made as part of the x conversion?
(@davidf) Have you experienced this with your new rebuild?
That refreshed engine is still in its crate, so I cannot answer or compare until I swap that engine and test.
The gearing seems different. For example, on the main straight at Cota I just barely get into 6th gear now after the rebuild, but I used to get into it much earlier. I have not reviewed data yet, but am running same best track times as before so I would expect corner exit speeds to be similar. Would the SM engine rebuild to the new "X" engine designation with improved clutch bearing have changed anything with regard to transmission ratios from the original 2021 SR3XX?
There are only two possibilities: 1) engine transmission gearing changed (unlikely), and 2) GDU ratio changed during refresh. I was at COTA last week with SR3 XX 1500cc and 3.07 gear ratio. On the front straight I was redlined in 5th gear; on back straight I was shifting into 6th well before the red and white curbing on the right, and hit 10000 rpm before the 250 brake marker, 140mph max speed on back straight. Easy fix regardless of case 1) or 2) -- swap out the gear ratio in the GDU. (I have one 42mm cut down socket left if you want to buy it. $85 shipped.)
The install after rebuild also included a new throttle cable and new throttle position sensor. But, now car has difficult time idling, seems too low. I need to look into adjusting idle up slightly.
Ugh. I had a similar problem which was caused by over-torquing the TPS sensor. I had to replace the sensor. Try loosening your TPS sensor screws so they are just snug. I suggest going through the entire TPS reset procedure which is described in engine guide (somewhere on this site). Also, you will want to be sure that your throttle cable is adjusted correctly so that you have little bit (very little) of slack at idle, and full throttle throw without stretching the cable. You can use the steering wheel to see the TPS value or PTMon. If you have questions call me. Details are very important in TPS and throttle cable adjustment. If you still have issues after TPS reset, replace the TPS, but low battery voltage can also cause throttle and idle problems.
More concerning is a very unusual shift issue has arisen for the first time. It occurred 2-4 times in three sessions. After downshifting for approaching corner, and rapidly accelerating from the corner, the engine or transmission is slipping (almost like downshifting momentarily) or hiccup, hard to explain. This primarily happening between 2nd to 3rd, but once or twice from 3rd to 4th, no other gears. This is concerning as quite abrupt acceleration ~1 second stall. Any ideas? Could it be some type of clutch adjustment (I have standard, not spin safe).
Ugh again. Download life data -- check whether your RPM is rising during those "slipping" events, or whether this is a throttle or fuel issue. I suggest delivering that data to SM asap. I am not an engine expert, but this is a concern.
I also recommend that you download and analyze Aim data from prior sessions and after refresh to compare exit speeds and RPM in each corner and straight. You should get an answer pretty quick on a couple of these problems just by looking at the Aim and ECU data.
I will be digging into data this week. I agree with your comments about gearing, no changes on my part, and my run experience prior with Cota is similar.
I found one of the hiccup spots, make sure you have sound on. Just exiting turn 1 at Cota upshifting from 2nd to 3rd. This was typical for the other ~12 times it happened all day. Normally exiting turn 1 and turn 11.
The ratios are the same in the even in the updated engine - standard Hayabusa.
That sounds to me like it is jumping out of gear under high load which is very strange to see.
Feel free to send me over the Life data and I can take a look through it for you, not saying I will seeing anything more than most but another pair of eyes can be useful.
As David mentioned resetting your throttle bodies/TPS may help the idle. Again strange that this has happened after a refresh when this should have all been set up for you.
Hi Dan,
Sean here from Spring Mountain Racing. Are you able to send us over the Life data so we can take a look at this so we can help solve the issue you're having with the vehicle shifting incorrectly.
As far as the X on the engine. The gear ratios do not change when we go in and update the input shaft bearings to the latest spec. If you're able to please send me your AIM data comparing the sessions before the refresh and the sessions after the refresh. I will have my engineer go through them and see if we can figure out what's going on with the top speed of your vehicle.
It definitely looks like an aggressive slip of a gear popping out, a slipping clutch isn't usually that aggressive, and it doesn't lose as much drive. It looks like you get a near instant 2kRPM surge.
We had/have a similar issue with one of the local members here, his GDU was the issue, the drive ring on the forward gear was popping out momentarily. I'd triple check all the adjustment on the reverse linkage cable.
I can't remember what the solution they had was but I seem to recall they just disassembled it/inspected it/found nothing obviously wrong and it worked after going back in. One of the original theories was possibly the drive ring on the shift fork was installed upside down from it's original position as it wasn't replaced either. I have no idea if they actually ended up flipped it, nor have I had my GDU apart yet to fully understand it's operation. I'm at the track tomorrow and I'll ask the mechanic. But your video looks basically identical to his complaint.
A slipping clutch isn't usually that aggressive, and it doesn't lose as much drive. It looks like you get a near instant 2kRPM surge.
Some additional clarifications: this was an intermittent issue/concern. I ran 4 sessions, it occurred in 2nd, 3rd, and 4th sessions, a couple times each. Each session has approx ~10 laps. In those turns 1 and 11 at Cota, coming from high speed to lowest speed on the track so engine was probably at lowest RPM when start upshifting after apex. There are a couple other turns that actually get down to 2nd gear, but I dont recall it happening at any of them and they are at higher RPMs thru apex. For whatever reason, it seems like the low RPM are contributing. I sent the requested data to Sean and Dan as requested, will see what comments are forthcoming. I just dont want to be damaging something with this new rebuilt engine, that exercise was painful enough.
UPDATE: I got consensus replies noted below from both Sean and Dan which are super detailed and helpful. I will work with my local dealer for resolution. Now, I am just trying to copy and paste the informative replies but the website keeps blocking.
Great info. I just want to re-emphasize that if/when you replace the TPS sensor, be sure not to over-tighten it. Just snug or barely snug. I learned this two weeks ago from dealers and Radical technicians. -- it is easy to ruin a TPS by simply over tightening the screws that hold it into position. When I replaced my TPS, the problems I was having went away immediately.
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So the only other problem to solve after the TPS issue is your gear ratio. Ask the tech that refreshed the GDU which gear ratio was installed, or see for yourself by removing the left side cover of the GDU. I think the standard gear set 3.07:1 is good for SR3 1500 at COTA.
My car has original standard 3:07 also, which is good universal for me at several different style tracks and HPDE only.
