Turbo Busa not revving past 7000rpm issue

[P44rgy]

I have a Turbo Busa fitted to the rear of my Austin Mini car. its running 0.7 bar (10psi) boost. On a recent track day, after 6 laps the engine struggled to rev past 7000rpm (10,000 easily prior to the issue). Any ideas as to what's wrong with it? My thoughts were plenum popping off then getting sucked back down again or fuel pump as fuel pressure was showing 3 bar. It has a Bosch 068 pump fitted and the fuel line from tank to pump are 7/16 (11mm) and 8mm from pump to engine. was thinking of swapping to the 044 Bosch pump.

 

[Hayabusa Wannabe]

Welcome @P44rgy. Cool car! I know that stumbling at 7,000 has been reported a few times.

For reference what year busa engine is this?

Some reported this issue with clogged secondary injectors due to lack of use. Is it okay with this setup to run a can of Seafoam through it? After some cleaning action the engine would indicate to you if this is an issue even if it does not resolve the problem completely.

 

[P44rgy]

Welcome @P44rgy. Cool car! I know that stumbling at 7,000 has been reported a few times.

For reference what year busa engine is this?

Some reported this issue with clogged secondary injectors due to lack of use. Is it okay with this setup to run a can of Seafoam through it? After some cleaning action the engine would indicate to you if this is an issue even if it does not resolve the problem completely.

Hi. Its a Gen 1 but has been fully built to take the turbo setup. Pulled 293bhp on the rollers and then did about 4 laps until it had this issue.

 

[202mphbusa]

are you watching or logging air fuel ratios?
I would do a quick compression test and leakdown then if everything check out you are not chasing a gremlin when you have a mechinical issue

Maybe cam timing jumped

 

[P44rgy]

are you watching or logging air fuel ratios?
I would do a quick compression test and leakdown then if everything check out you are not chasing a gremlin when you have a mechinical issue

Maybe cam timing jumped

Thanks. Im not watching or logging air fuel ratios. The engine build is brand new. Done a few hours being bedded in on an engine dyno then some runs on the rollers. You don't think the plenum idea or 3 bar fuel pressure are anything?

 

[202mphbusa]

Plenum could have lifted
I have mine bolted down since my first bike incarnation

 

[P44rgy]

I'm going to fit Schnitz throttle body clamp and then strap the plenum to the throttle bodys.

 

[202mphbusa]

I'm going to fit Schnitz throttle body clamp and then strap the plenum to the throttle bodys.

Fixed ?

 

[ColdBusa]

The plenum blowing off would not stop the engine from revving up. I've had it happen while making a pass, all that happened was a loss of power. The fuel will compensate with the loss of MAP and decrease accordingly (depending on how you have it set up).
I'd be leaning towards a fueling issue. 3 bar (43PSI) is decent fuel pressure for low boost conditions, but was that 3bar at idle? If you're not monitoring it, could it be dropping when loading up the injectors leading to a possible fuel filter issue? What fuel are you running? Depending on the fuel, are you flushing the system post use (Q16)? When were the injectors clean/flow tested last?
However, for something like you are running it's highly recommended to monitor and log the basics to troubleshoot issues like this.

 

[202mphbusa]

Plenum could have lifted
I have mine bolted down since my first bike incarnation

A funnyish story
I was at DAS Eric was turning up and tuning my bike
at the time it was non intercooled little (28/76 from memory) turbo

boost unlimited plenum kept lifting so we stuffed a sweat shirt under the tank......nope
block of wood and belt sander to get the thickness right she held 28psi and made 382 HP thru S2000's and a FMU