Important! : What RPM

23rd July 2017, 22:42

Hi all
Just looking for some advice on max rpm for standard internals.
I have recently done a lot of work on my vts race car and spec on engine is as follows.

Catcam 743,s

Head ported/polished, skimmed .5 and valves cut in .3 running 210psi compression.

Gsxr 1000 bodies with 50mm velocity stacks

All new bearings rings and seals OEM

Running on omex 600 ecu

Mapped at 174bhp 170nm

The rev limit is set to 7450rpm but the car feels like it wants and needs to rev higher. I have they are fine to rev to 7800rpm on standard internals but would anyone here have any knowledge of this? Video link below is some testing I was doing after mapping on bodies. Limiter creeps up quite fast!

https://youtu.be/crUw_4xaIts

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24th July 2017, 11:53

All depends on your powerband, if your still making power/torque after 7450rpm then you should raise it. I cant view the graph any larger in work to see where your powers dropping off.

24th July 2017, 14:15

still on hydraulic tappets I presume so I wouldn't go any further than that especially with a race engine.

torque seems to peak particularly high which suggests the timing is a little retarded, which will accentuate the feeling of urgency up top.

however I'm not sure of the valve clearance on your bottom end vs that cam spec.

24th July 2017, 21:58

Quote:

Originally Posted by Synister

All depends on your powerband, if your still making power/torque after 7450rpm then you should raise it. I cant view the graph any larger in work to see where your powers dropping off.

Yes looking at the graph it seems to be still pulling. Even driving the car it feels like it wants to rev a little more.

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24th July 2017, 22:09

Quote:

Originally Posted by welshpug

still on hydraulic tappets I presume so I wouldn't go any further than that especially with a race engine.

torque seems to peak particularly high which suggests the timing is a little retarded, which will accentuate the feeling of urgency up top.

however I'm not sure of the valve clearance on your bottom end vs that cam spec.

I was always a little nervous of clearance as the say the 743 is a about as aggressive as you can go with standard pistons. They have been correctly timed in by the engine builder who is also the guy that mapped it. He thought if we increase the rpm it could make a little more power. But he didn't want to risk it as he didn't build bottom end, as that was done by myself. I think your right about torque as before the bodies were fitted that figure was lower in rev band but it lost 2nm with bodies and gained 8bhp.
The car feels quick but I just feel it needs a little more rpm, only not sure is it worth risk.

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24th July 2017, 22:14

When the car was pretty much stock apart from full exhaust and good induction it made 139 Bhp.
See graph below it was hitting limiter at 7800,ish
I know that's not normal so I'm thinking someone before I had the car may have raised that limiter!

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27th July 2017, 21:53

You probably need a longer intake to bring the torque down the revs a bit. Unfortunately that means tipping the engine forwards or cutting the bulkhead.
7800 is fine.
The revs shown on that Dyno-Dynamics plot is calculated from road speed, so it's not unlikely that the reading is incorrect.

27th July 2017, 21:58

Quote:

Originally Posted by Chipwizards

You probably need a longer intake to bring the torque down the revs a bit. Unfortunately that means tipping the engine forwards or cutting the bulkhead.
7800 is fine.
The revs shown on that Dyno-Dynamics plot is calculated from road speed, so it's not unlikely that the reading is incorrect.

I'm actually working on an air box at the moment with 78mm cold air feed pipe. I really felt the effects of the car sucking in so much hot air In my last race. Thanks I think I'll up it to 7800! That with the new cold air feed should really help

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