Supercharged 450 running out of puff !

[Richard 858]

Since getting a tighter belt sorted for my supercharger I've noticed that when pushing on the motor is starting to cough & splutter a bit at 5,000 rpm +. I'm putting it down to fuel or air starvation or spark when at full chat.

I have a single Pipercross air filter fitted to ACT silicone inlet hose (into larger Bosch AFM), standard fuel pump (but green giant injectors) and Lucas 14 CUX (let's not start that argument again though !)with decent leads & NGK 7 grade plugs.

Was making 415bhp with some belt slip so it seems it's just the extra top end load from a non-slipping supercharger that is causing the issue.

Any ideas welcome. Thanks in advance.

[spitfire4v8]

Was it mapped with a slipping belt then?

[Richard 858]

At the time of mapping the belt just started to squeal a little when over 5,000 rpm. Gradually got worse after that until I fitted the tighter belt. On reflection I suppose this could be the reason but I'm also beginning to think that the standard fuel pump might well be at it's flow limit (or a bit beyond).

[Duke Thrust]

How much boost are you running?

Could be the sparks being blown out (had this problem on my Noble)

[neal1980]

I would speak to Hoofa im sure he had problems with the supercharger being too small and not being able to flow as much as he wanted. You may have found your brickwall but I hope not....

[Richard 858]

I'm only running 6 psi of boost and have the larger C38 supercharger. I'm still inclined to fit an uprated fuel pump and perhaps go for a twin air filter set up to remove another potential restriction, will this madness never end !!!!!!!!!!!!!

[spitfire4v8]

Might be an idea to do some testing before throwing money at it willy-nilly fashion

[900T-R]

spitfire4v8 said:

Might be an idea to do some testing before throwing money at it willy-nilly fashion

This. Always a good idea.

[Pupp]

Maybe close the plug gaps a tad in case you're blowing out the spark (really). How do you know the boost is *only* 6psi?

[blitzracing]

If you are still running the lambda probes you can do a direct voltage measurement across the black / white wires. If you get 1.2 volts or more at full power it wont be fuelling. If its zero volts its running very lean or your sparks are going out- If you are running out of fuel, you will see the lambda voltage drop of before it gets to the point of misfire. I now have a vision of some poor passenger holding on for dear life, whilst trying to read a DVM, as you hit 150 MPH.

[Bluebottle]

My original install ran lean over 5K rpm due to the original stock fuel pump (you are right on the limit of its max flow rate) and that's assuming its in good condition also,
I found that my fuel filter (which I had paid every year for a new one in the service) looked about 15 years old and definitely was restricting flow.
personally I would be fitting a Bosch 044 pump and filter regardless with an SC install.

Other things to check;

check the fuel regulator, if MA mapped your system then I guess its stock Bosch? if so did he replace it when you had it mapped, my old one didn't like the increased suction from the FI so I had to renew it?

Check the vacuum advance diaphragm on the Dizzie is still working,the extra psi suction tore the diaphragm on my ancient crispy critter so had to replace it.

[ChilliWhizz]

Bag of Maltezers says it's not getting enough air. Or maybe fuel. But if you fix the fuelling then you won't be getting enough air. A well known guru identified this problem on beastie, and I'm sufficiently confident to wager a bag of Maltezers on it. Although if I win I'd rather have wine gums.

Chilli

[macdeb]

Firstly, WOW! 415hp on Lucas and only 6psi boost?? respect
I'd guess problem could be fuel regulator or fuel pump maxing out as has been said.

[fatboychim]

Bluebottle said:

Check the vacuum advance diaphragm on the Dizzie is still working,the extra psi suction tore the diaphragm on my ancient crispy critter so had to replace it.

This happened on mine.


Have you fitted the BEGI fuel reg? Also I think Bluebottle runs the twin air filter as well

[Bluebottle]

ChilliWhizz said:

Bag of Maltezers says it's not getting enough air. Or maybe fuel. But if you fix the fuelling then you won't be getting enough air. A well known guru identified this problem on beastie, and I'm sufficiently confident to wager a bag of Maltezers on it. Although if I win I'd rather have wine gums.

Chilli

Yeah I wandered about air to, but if the was an air restriction it would just feel flat and assmatic and not cough and misfire?

[Richard 858]

Thanks for all the advice chaps.

Boost was measured with pressure gauge at Rolling Road session with MA.
Standard fuel regulator is still in place but looks to have been squeezed a little to up the fuel pressure slightly (according to MA).

I will check/adjust as many of these suggestions as I can over the weekend (although I'm not sure the missus has the nerve for a consistent high speed run with voltmeter in hand !) and report back when issue is sorted.

[neal1980]

Sorry I assumed that the pump would be replaced as part of the conversion. That is seriously pushing it to beyond what it was designed to do and leaving you with NO room for safety.

I would replace ASAP, cant believe you have got it over 400bhp on the standard pump so it must be a great engine @ 6psi!!

[SILICONEKID345HP]

Those 088 pump cause havoc with the fuel system ,i would fit one of those tanks ,what ever they are called .

[Sardonicus]

Pupp said:

Maybe close the plug gaps a tad in case you're blowing out the spark (really). How do you know the boost is *only* 6psi?

^ This its quick and cost nothing and certainly worth a try I would before you start getting involved

[Bluebottle]

Sardonicus said:

^ This its quick and cost nothing and certainly worth a try I would before you start getting involved

Bodge it, or fix the problem, your choice...plug gap is not the problem.