Where has power above 7K gone

The Oily Bits S1 Specific Topics
1

Before I do my next mapping session in the coming week I was hoping to get some opinions and options to try either before or on the day. My predicament is that the engine is not making power above 7.5k, starting to taper off by 8k, did a power run on a dynapack up the road today as our rolling road only does readings in 1000 or 500 increments and I wanted to see what the curve looked like with a bit more resolution, will post them hopefully tomorrow, their printer was broken.

Here is the spec since December build:

Head:

VHPD

  • Ported a while ago locally (how good I don’t know it is difficult to say unless I flow test it but looks ok when comparing to what Dave says should be done on his website, lets call it an average port for arguments sake)

  • Std VHPD valves

CAMS

1444 - timed to Lobe Centre specs as supplied
Double springs and re shimmed to spec

Exhaust

Motorsport series exhaust manifold - I can’t tell the difference between janspeed/ebd etc so it’s propably one of them.

CRP

Eliseparts Backbox - re packed during rebuild

INLET
Jenvey 45mm individual throttle bodies with their manifold
Trumpet extensions as discussed previous threads

Fuel

102.6 octane leaded race fuel as supplied locally.

Not to much else, I am not by any means unhappy with the performance or torque figures which are now better than I have ever had before, I expected more from the cams, in that even though their duration was 4 degrees less than VHPD the lift was higher so should get more torque and smooth out the power at up to 8500rpm.

What I am saying if anyone comes across this page through a search is that the 1444’s have done more than I expected in the middle and have improved HP slightly, but most definitely are helping torque. Would hate someone to interprit this as slagging the cams.

From What I see my options are as follows:

  1. adjust cam timing to move power curve up and help it make power to say 8300 and rev limit at 8500rpm still having decent power at that point.

However what effect will this have on my torque peak because I like that just where it is, gear change at 8K puts me at torque peak which is great.

  1. leave the damn thing alone and be happy that it is making more power than it was 1000RPM lower and more torque than ever, and just keep rev limit at 8200rpm for those occasions on track where i want it to run on a little longer, but keep shiftlight at8k which is great for torque.

Dave I have not re timed the cams yet using Lift a TDC method as I first want to establish what effect that would have on my curves, but it is on my pre race checklist for next week to check cam timing for reference while the back is off the car.

What does the collective think, is there something small I am missing that will let it do better at 8+k, something like, oh it’s silver, no those don’t make power past 8k should have kept the orange one mate

2

You could be running out of fuel flow. Have you changed the injectors/regulator or fuel pump.

3

Do you have a fuel reg., and what pressure are you running?

4

Running 300cc injectors at 3.5 bar with in line bosch fuel pump, mounted to a gravity feed pick up welded into the bottom of the tank, fuel pump is mounted below tank level. Fitted adjustable FPR as well ages ago.

According to the emerald software good for 240hp, used to run 4.2bar with the std injectors before the mods but knocked it back when I fitted the 300cc’s. My thinking was that after looking at the pump specs it flowed more litres at lower pressure, and should still give me some headroom with injectors operating at a max of 87%. However it might be worthwhile taking the pressure up to 4bar again and having injectors operate with alot of headroom, never a bad thing. Not even a situation I had considered so thanks for the input even 5f s4–3y 5s fine once i have confirmed it I can take it off the troubleshooting list.

Russ since 1 January leaded fuel has been removed from sale locally, however the tracks supply and regs say that 100 or 102 octane fuel may be used, it makes my life easier because the tracks sell it so I don’t have to cart fuel around with me.

5

Jason, was the engine making good power above 7200 before and this is a change? or it never did after the rebuild?

6

Hi Uldis,

It has always been flatter from 7k to 8k losing perhaps 1 or 2kw, but pretty much a flat curve. I am going to try and get around to checking the cam timing today, if they seem way out then I will adjust and see what it feels like. Overlaying my collection of graphs last night, different dyno’s on most so numbers don’t mean anything but the shape of the vhpd and 1444’s has been consistent. The VHPD’s started making decent power at 6k and flattened out from 7k to 8k. The 1444’s have a better torque curve everywhere and with a rev limit of 8k would still be far better than the VHPD’s. it’s just worrying that power is falling away, love the mid range and don’t want to lose the torque or where it’s peaking at the moment,so unless cams are way off I will leave them as is.

Spent some time studying a selection of emerald maps last night and strangely all my maps have a constantly increasing rate of fuel from say 6k to 8k whereas many of the more aggresive maps I looked at have the fuel tapering off slightly at 8k, difficult to make any assumptions without an AFR curve but does this ring a bell with anyone, overfuelling at the top in my case.

7

I don’t have my maps now with me but from memory theu taper off slightly like you say.
I assume you have checked my power graps here.

The cam timing has not changed between runs because I wanted to isolate the effect of the induction and exhaust manifold design.
From my limited experience exhaust design has a lot to do with the shape of the curve, and you can see on the JV3 design the pwerband is from 5 to 8K. I like it like that but we’ll try a slightly different one soon.
I would say, try with 100-130mm trumpets to start with, and if possible something like the JV3 design (straight through & balance pipes).

Make sure your engine is well balanced for high RPM use though, otherwise… bad things can happen

8

You would expect the fuel slope to closely follow the torque curve, not the power curve, so as torque is growing, so will the fuelling, as torque falls (and it usually does above 6500) so fuel will fall. If the fuelling remains constant from peak torque to peak power and assuming that the fuelling is right at peak torque then there will be a degree of overfuelling, sometimes this is done to dampen the incoming charge and reduce the possibility of detonation, more often than not it shows that the engine has not been closely mapped at the peak power figure and that the fuelling has been extrapolated and then checked by a run with the fuelling logged. Rich is better than lean at these engine speeds but both rich and lean are power sappers.

Dave

9

Had the car back on the dyno on Wednesday, re timed cams to 143/113, they were quite far out and after re timing it felt alot better.

We managed to sort out the hole below 3000rpm quite nicely, and it made max power at about 7300rpm, the max is not logged on the graph as it is a load dyno and we only log the graph in 1000rpm increments, but we consistently saw 102kw at 7300rpm. Yes I could propably go shorter on the trumpets to get some more power to 8k, but just look at the mid range improvement, I have worked out my gear graphs and changing at 8500rpm in first and 8000rpm for 2,3,4 and 5 puts my rpm drop at max torque in every gear, so to be honest I am rather going to keep the mid range torque , although peak BHP figures would be nice I am super happy with the torque spread and placement. I have overlayed the latest curve on top of the last VHPD map we did, same dyno.

Thanks to Dave for the cam timing figures and Uldis for sending me his maps for perusal so I could get a better base map before the Dyno.

[image] MWEB Homepage [/image]

Well chuffed, lets hope I can make some use of that mid range on Sunday

10

Excellent!, good you managed to sort that one out.