Supercharged apex....won't spin past 9000rpm

[Woody255]

Hi all,
I have an Apex built for snow drags with an MPI s/c, stage 2...2 1/2. Running 18-19psi at 10,400 on pure C14+. PC5 with Autotune, POD300 data logger etc. This was built a few years ago and has dominated the local snow drags. At the end of the season, I began having a few issues with the throttle bodies coming lose, as I did not have them tethered down securely. That has been resolved, and all was good. At the last heat of the day, I could only run up to 9000rpm, and I still cannot figure out why. No abnormal noise, both S/c belts are good, throttle bodies secure etc. AFR readings are proper, clutches look fine...any ideas out there? Thanks. Woody

 

[gouldsjett1]

Check your boost tube connections from the s/c to the front of the intercooler.

 

[kinger]

Have you changed anything in the clutch recently?

 

[Woody255]

No, haven’t changed anything. It was working great, and the very next pass it wouldn’t pull the rpm.

 

[maim]

how heat soaked was the sled? where clutches hot?

 

[MrSled]

No, haven’t changed anything. It was working great, and the very next pass it wouldn’t pull the rpm.

I would do a leak down test. Don’t sound good. How much boost?

 

[kinger]

Have you checked the throttle blades are opening fully at WOT?

 

[Woody255]

It did not get hot. Engine runs perfectly, just simply won’t climb to full rpm. My first though was a SC belt failure, but they are ok....I will do a compression test to be sure, but I do not think it’s an engine problem.
Mr.Sled, 19psi

 

[mbarryracing]

Does it rev / pull hard right to 9000 rpm then flat-line?
Same with boost? Jumps up then flat-lines? If so, maybe if your SC has an internal sprag type clutch it might be that it's now junk / slipping when reaches a given boost level... Seen that happen on certain model MPI SC's (aren't repairable), and have that happening right now on a SC Wave Runner.

 

[Woody255]

Does it rev / pull hard right to 9000 rpm then flat-line?
Same with boost? Jumps up then flat-lines? If so, maybe if your SC has an internal sprag type clutch it might be that it's now junk / slipping when reaches a given boost level... Seen that happen on certain model MPI SC's (aren't repairable), and have that happening right now on a SC Wave Runner.

Yes, that’s what’s happening. All seems well until I run 100% throttle. Happen to have any photos ? Thanks

 

[stone88]

Check for boost leaks

 

[Woody255]

Update here...found the vacuum line coming off the BOV was severely cracked. Fixed the hose, problem solved.

 

[MrSled]

Update here...found the vacuum line coming off the BOV was severely cracked. Fixed the hose, problem solved.

Nice!!! at least it was inexpensive!

 

[NOS-PRO]

Update here...found the vacuum line coming off the BOV was severely cracked. Fixed the hose, problem solved.

Awesome!