Race engine down on power - Saxperience

boylin · 24th May 2019, 17:37

Hi, bit of a long one this, but any help is gratefully received!

I have a saxo VTS that I use for trackdays. I inherited a supposed race engine a few years ago in another vts and after swapping the head, cams etc it is finally up and running and in my own saxo. The problem is it’s down on power. Spec of the engine is as follows:

JP4 bottom end (I think, as it didn’t have a breather pipe next to the dip stick).
Wossner high comp pistons
Forged rods
Race bearings
Arp rod bolts
J4 head- standard valve size
Ported and polished, and skimmed (unknown amount)
Catcams 274 duration (1321737) cams along with uprated springs and retainers
New set of hydraulic lifters
Catcams vernier pulleys
AT throttle bodies
Clio 172 injectors
4.5bar FPR
Mtech V4 ECU (megasquirt)
Running on 98 octane

After having a nightmare setting the timing to the catcams spec, we took it to be remapped at Mtech automotive (the place that had made the ecu in the first place). I was expecting about 180bhp. It developed 142bhp. The remapping guy said it was performing very flat and suspected cam timing to be out. Took it away, checked everything, cam timing was out, reset to catcams spec, checked about a thousand times, took it back to remap again, 143bhp. We’ve played about with cam timing on the rollers and got it as good as we can get it- developing 148.5bhp. Inlet cam made a big difference to the power curve, exhaust cam advanced and regarded by around 5° made no difference. The remap guy said this was unusual. He says the fuelling is now perfect and there’s nothing more to be done from a remap point of view.
Only 2 things we can think of now are low compression ratio or faulty cams? Annoyingly when the engine was in bits I never calculated the compression ratio, could this be something to do with having a J4 head on a JP4 bottom end? And also has anyone ever had any problems like this with catcams before?

Sorry for the long post. I want to try and cover all angles before stripping the thing down again!

Chipwizards · 24th May 2019, 21:11

Check it's getting full throttle.
Fit stock cam pulleys and pin it up, that will get the cam timing close enough to eliminate that variable.
If that doesn't fix it, take the lambda bung out and do a pressure test while doing a power run; if it's more than about 3 psi your exhaust is no good.
If that's OK get someone else to dyno it, check the power, fueling, ignition timing (actually measure it, under full load at high rpm- it will want to be around 24 degrees)
Check the timing on all cylinders, because with a megajunk ECU you never really know what is happening.

boylin · 25th May 2019, 07:17

Thanks for the reply. We did check it was getting full throttle. If I put the standard pulleys back on and set it up as standard will that work with these cams? These cams have been set up to catcams spec with a DTi gauge. That’s a good idea with the exhaust, I think I’ll start there.

Cheers