Setting the car up - an update.

The car was now setup and ready for it's first track day, however there was something that we thought was not quite right, the bhp we were producing seemed a little low. Whilst 157 bhp was a good performance gain and is still a lot of fun to drive, we were hoping for about another 10 - 15 bhp more from our set-up. This led one of the more mechanical owners of TrackBitch to head to the forums and enquire about what we have got, with some interesting responses.

We had measured the boost pressure from the carb top whilst most owners of Renault 5 GTT measure them from the carb base as you lose 4-5 psi through the carb itself and it gives a more accurate reading as to what the engine is actually getting. This could mean the car has even more potential than we think. See some thoughts below:-


With regards to BHP
Our rolling road said - 143bhp at the wheels but calculated 157.6 bhp at the flywheel. When the rolling road calculated flywheel BHP at the start he calculated a drive train loss of around 20%. For some unknown reason once tuned he calculated a drive train loss of about 10% - which is physically impossible. Drive train loss is much more consistent, if anything it is more at low power NOT less, in his calculations for us drive train loss changed and was FAR more at high power?

Talking to the guys on RTOC.org and using a 2wd loss calculator on line it is FAR MORE likely that our flywheel power is now 170bhp.  You can do the same by entering your drive train type (front, rear or 4 wheel drive) and wheel HP here
http://www.dyno-power-run.com/dynocalc.shtml

If you enter fwd and 143 whp in to this calc it gives our car a maximum 170bhp and a power to weight of 205bhp per tonne. We still have the option to safely add about 3 psi of boost (due to setting up at around 15psi carb base instead of 18psi carb base).

So we can probably expect 180+ bhp in the near future.

Ultimately what really matters is wheel horse power - torque at the wheels is the only accurate measurement a rolling road can offer, but as manufacturers use flywheel horse power (because they dyno their engines on a bench not in the car) then we have used flywheel bhp for comparison to other cars.

Lastly, we don't think we have a lazy turbo - we think at high boost (20psi +) we may well have a boost leak, probably at the wastegate, due to wastegate creep (probably caused by our poorly T3 actuator - which has no adjustment in it) or a possible leak elsewhere in the boost pipe work or the inter-cooler.


The full posting can be read on RTOC but you'll need to sign in to read it.