Here we go, dirty washing in public and all that
The car has been up to Vince Mosley's rolling road in Llandeilo for a bit of testing etc. Vince has up dated his whole set up and has computerised the road plus added a weather station to correct the data for all sorts of atmospheric variations.
Between Jason and I we have made some changes to the engine earlier this year. I added a different exhaust manifold to suit the chassis mods based on a Miltek 4:1 system. Broadly similar to the heavily modified Ashley I ran before and agian modifed to suit the head which has some big holes in it! The head was modified by Jason with the valves up from 40.5mm to 42mm and additional porting to match. Having driven it a few times it felt well good but with 750kgs and over 200bhp it was allways going to feel lively
. It felt a bit flatter low down but picked up nicely. having seen the first plot it was clear that it was flat bottom and and then picked up strongly higher up.
Due to the changes to the rolling road the data this year will be different to the un corrected data from last year although we have the uncorrected data available as well. We spent a while checking and adjusting fuel and ignition maps to see what effect they had. There didn't seem to be many changes required other than at the bottom end, up to 3000rpm where it was down around 15bhp on where it should have been.
Generally a disappointing day as we started off down on power with a big hole around 4500rpm. After an hour or so we had the blue map. It just didn't really want to make peak power. Ok it was running to 8000rpm and still holding power but it wasn't really peaking as you would expect around 7k or so.
We then played with the cam timing. We tried retarding it a degree but this made it worse so we then advanced it and whilst it still didn't want to peak we added a dgerre or two at a time and we eventually ended up with the green trace. This is the opposite to what we did last year to gain power, we are essentially back where we started with last years engine when we first put it on the rolling road.
Analysing what we have got and comparing to the last plots uncorrected figures we have 183bhp max at the wheels (176bhp corrected). This years figs were taken in 5th gear and I'm sure last years were taken in 4th, based on that and just for a like for like comparison we would have about 219bhp at the crank. So like for like about the same but we should have more that that, I would have thought we were 4 or 5 bhp short of what I would have expected on that basis.
Going back to corrected bhp we have around 170+ bhp at the wheels from 5500rpm to over 7500rpm in a very linear form, with a slight peak at 6000rpm where we have the 176bhp, which is around 206bhp at the crank so not too shabby for an 8v but not what I had expected.
There is 10 or 15 bhp in there somewhere but where?
Whilst a little disapointing on the day it is now quite interesting to find out where the power is. After a couple of hours on the rolling road everything was overheating, petrol vaporising etc so we gave up.
Jason is convinced much of it is cam timing, I don't think it's that simple. I think the obvious culprit is the exhaust manifold, whilst very similar I've an idea the primaries were a few mm smaller that the Ashley. It's all ok in side as I cut it up to check and tidy it up. Maybe the valve dia increase has in some way affercted the induction length as well? I need to get some data over to Jason to have a look at and whilst I won't put all the answers up here I'll give you some clues what we do
Once we have list together I'll record where we are settings wise, do some checks and then re set it up and we'll run it up again and see if we can find the rest of the power.