I have recently upgraded my engine, but am getting worse performance than before (15.5 sec 1/4 mile vs 15.2), and I can't figure out what is causing it.

My EF is running an AU engine with an EF head. Mods to date:
- SS Inductions snorkel
- Amsoil 2-stage foam panel filter
- bell-mouthed 3" airbox exit
- Territory induction tube
- 68mm throttle body
- port-matched manifold
- 10mm phenolic manifold insulator
- Bosch '931' 267cc injectors
- Autolite 985 projected-tip spark plugs
- vernier adjustable cam gear
- Crow 7739 valve springs
- Coby F19CP headers w/ cat delete
- TI Performance J3 chip and tuning pack
- high-stall torque converter (2700-2850 rpm)

The previous head was a non-Tickford EF (39mm exhaust valve) with ported exhaust and lightly tidied intake, skimmed for 9.7:1 compression. The cam was a Franklin RH24B (196/192 deg @.050, 113 deg LSA, .265/.252 cam lift). AU MLS .65mm head gasket.

The new head is an EF XR6 Tickford (41mm exhaust valve) with ported exhaust, pocket ported intake, 4-angled seats and 3-angled valves, equalised valve heights, deshrouded valves, polished chambers, skimmed for 10.0:1 compression (with graphite gasket). The cam is an Auckland Cams 1258 (208/198 deg @.050, 114 deg LSA, .258/.243 cam lift). Graphite 1.4mm gasket (to seal the corroded coolant ports in the block, the reason for the rebuild in the first place).

With the better flowing head, higher compression, and hotter cam, I should be getting significant performance improvement, but it’s actually worse than before. I swapped the old cam back in to see if that was the problem, but it made essentially no difference.

I have adjusted the vernier cam gear to get maximum performance, after testing various advance and retard settings. I have also adjusted the ignition advance to get maximum acceleration at each rpm/load setpoint (starting low and adding 2 degrees at a time until it stops improving) – ending up at 26.5 degrees maximum advance. I have set the WOT air-fuel ratio at about 12.2 at peak torque, rising to 12.9 at redline (according to my WBO2 sensor). There is no audible detonation, but maybe the knock sensor is sensing knock and pulling out timing anyway.

I am stumped as to why it is performing so poorly, so I did a compression test (warmed up, throttle open, plugs out):
1 147
2 152
3 150
4 143
5 152
6 135
That’s a lot lower than it was before (about 175), but then the cam has more duration (6-12 deg), and the cam timing is likely a little different. It is also a lot wider range than it was before, and I am a little concerned about #6. I expected quite a tight range. I can’t find any evidence of a head gasket leak.

I also read the plugs. They are all very similar, and this is an example:



The insulators are almost completely white (a few have a small amount of very light tan on one side), and they all have varying amounts of black (and reddish?) speckling. The ground strap does not change colour at all, but stays light coloured all the way down. These are brand new spark plugs, gapped at 1.1mm, the same Autolite 985s I have been using for many years with good insulator colour and strap colour change at the start of the bend. I have tested the resistance, and they are all in a narrow range. I can’t imagine that the head and cam changes are significant enough to require a cooler plug. I know it’s not running lean, as I have logged WOT AFRs multiple times in the 12.2-12.9 range. The fuel is BP Ultimate 98 octane (no ethanol).

I am at wits end, as nothing is making sense, so would appreciate any suggestions you might have.

Thanks for your help.

I have to ask why did you take the AU head off??? cos it totally different to the EF head not only that but the valve timing is different!! I have a AU motor in my EL yer sure I don't have all the other things you have but I have changed the cam chip in the ECU high flow cat with headers and 2- 2/1 exhaust and SS Induction, she 195kws

I have to ask why did you take the AU head off??? cos it totally different to the EF head not only that but the valve timing is different!! I have a AU motor in my EL yer sure I don't have all the other things you have but I have changed the cam chip in the ECU high flow cat with headers and 2- 2/1 exhaust and SS Induction, she 195kws

The AU bottom end with an EF/EL head is a fairly common setup. Think of it as a block swap. As the crank gear, cam chain, cam angle sensor, bolt patterns, etc are the same as the EF/EL, retaining the EF top end is straightforward. The cam timing works the same as on an EF block.

The EF head - especially the Tickford XR6 - flows much better than the AU. What you effectively end up with is an EF engine with the NVH improvement and built-in windage tray of the AU - the best of both worlds.

I bought the freshly rebuilt engine as an AU bottom end with an EF top end. Like I say, it's the best of both, so it was what i was looking for. And the previous non-Tickford EF head worked just fine on the AU block, so the problem I'm seeing cannot be an issue of EF vs AU head.

It sounds like your AU engine is very stout. Based on the mods I have done to my engine, I would expect to get 160-170 rwkw. I had it dyno'd at 150 rwkw with the old, tired EF block before many of my current mods.

Well, the compression isn't the reason for the poor performance. I tested it again, and had a d'oh moment. I am unable to see the pressure gauge from the driver's seat, so I was turning it over exactly 9 times, as that has previously been enough to max out the reading. It turns out that the pressure is increasing only about 15-20 psi per turn, so 9 revs was not getting it to full pressure. It takes more like 12 turns to hit peak psi (maybe that tells me something). Now that I have measured it correctly, it averages 175 - about what it was before - with a high of 192 and a low of 164. This is about what I would expect from a slight increase in compression ratio and cam duration.

So I'm back to square one.
- good compression
- cam timing tuned
- AFR tuned
- ignition timing tuned
but less power across the board than before the new head and cam.

Do the spark plugs give us any clues?

Any suggestions would be much appreciated.

So where did you end up setting the cam timing bud

I also think ignition timing is way to low.
I personally suggest upping your timing to 34 degs total.