4.2l give or take 300ccs

[fatjon]

I just started stripping down my soon to be turbocharged AJP and can confirm what has long been suspected. It is a late 4.2 engine number p4200-891, it was lifted out of a 99 cerbera 4.2 and it is in fact a 4.5, 91mm bore, steel crank, etc.

little wonder there are so many folks claiming their 4.2 is as fast as a 4.5, it probably is a 4.5.
Bloody shame I had already ordered the 4.2 head gaskets and bearings, DOH!


Jon

[brogenville]

Good stuff jon- it always did feel a very strong engine. I take it the heads and everything looked standard?

So if you're using standard head gaskets are you just intending on keeping the comp ratio the same?

[fatjon]

No, can't get away with enough boost to be worthwhile at 10:1. Accralite are making me a set of pistons with the CR dropped to 8.2:1

Should be able to run up to about 18 PSI, its not going in the Cerb though, at least not yet, but we are making the manifolds the right shape so it could be done later.

Jon

[brogenville]

Custom pistons eh? I take it they're not already on order!?

Are you willing to make any predictions of bhp at this stage?

[fatjon]

Fortunately not! Had a long chat with one of Accralites technical chaps a couple of weeks ago and he is of the opinion that full skirts would be better than just making new slipper pistons with a lower crown. He reckons they will distort and cause poor sealing at this level of power. The argument seems logical and they have a lot of experience in such matters. Having stripped the engine a new complication came to light, the clearance between the bottom of the pistons and the crank webs at BDC is very small indeed. It looks like the answer will be somewhere between the two with a bit more skirt to support the piston but short of a full diameter one. Have to do some careful measuring tomorrow to see whats possible then send them a piston and a few measurements and photos. Also need to swap the head gaskets and bearings for the 4.5 versions. TVR, love em but they really are a rule unto themselves.

We are hoping to make around 750BHP reliably, maybe more if we push our luck. I have a pair of Garrett GT2860RS turbos with a 0.86AR housing and a few tweaks so the limit is 800BHP after which the turbos move out of their maps. The plan is to use an Emerald ECU, I have one on the Cerbera and I'm impressed with it, plus it supports odd fire engines which is handy. Can't wait to see how long the T5 lasts when we hit it 700-800BHP!

The car is pretty much prepared in terms of the bodyshell and suspension. I'll post a few pics tomorrow, as I said it's not a cerb but the engine part of the project may be of interest to the cerb community.


Jon

[DonnyMac]

Hi FJ,
Please keep this thread updated, I've bookmarked it.
700-800bhp, now there's a thought.
D.

[brogenville]

Interesting you say that about the emerald supporting odd firing orders as i was talking to track car joo a few weeks ago about the differences between the emerald and mbe ecu options, and (don't think I'm dreaming this up) I seem to remember him saying that "technically" the emerald doesn't support a 75 degree flat v8, but that for some reason it actually results in a better mid range torque. I cant really remember exactly what he said- but does that make any sense to you?

[fatjon]

The standard Emerald K3 did not support odd fire engines but Dave Walker and his programmer did a special firmware just for the AJP. Without odd fire support on a 72 deg V8 with a flat plane crank every other ignition event would be 15 (ish) degrees out. The big difference with the emerald in the mid range is that (if you forget emmissions) you can correct a major hole in the fueling map. Take my word for it, the car is transformed. There is a lot of talk about absolute BHP as the main criteria for performance but what really matters in a dyno curve is the amount of area under the line which shows the true performance of the engine as it accelerates to its ultimate output. Is easy to make an engine do 1000BHP in a rev band of 500 rpm with virtually nothing either side but it will be eaten alive by a well tuned ford fiesta unless it has 18 gears to keep it in its power band. I'm not party to the firmware of the Emerald but I think I know where Joo is coming from. A flat plane V8 is in reality 2 four pot engines on a common crank, so in software you can treat it as 2 engines, each followings its own sequence but 180- 72 and 180+72 degrees apart, viewed in that way it's true to say that an ECU can either handle it as one complex engine or 2 simple ones. Not sure which way the MBE or emerald handle it but TBH from a tuning viewpoint it's not important provide it gets the spark to the plugs of each bank at the right crank angle. I rather suspect that since the MBE uses 2 lambdas and 2 throttle pots with separate correction tables for each bank that it also treats the AJP as two four pot engines. I think Joo has done some work on the MBE code, maybe he can shed some light, are you out there Joo! BTW Joo , the cerb passed its emmissions on monday, thanks for your help!

Jon

[trackcar]

Broges yeh you misheard me .. the reason I was suspecting for the better midrange on the emerald is that i'm absolutely convinced the crank offset theyve got is wrong by 10degrees. 0 degrees timing on the emerald is actually 10degrees btdc. i think it's an injector firing timing which is different on the emerald by 10degrees compared to the mbe. I'm not sure, and havent seen a figure for the mbe yet, and i'm making a lot of assumptions not least of which that batch firing and 10 degree change on injector timing is going to make any difference at all. but fact is if you swap an mbe to an emerald and bespoke map them both the emerald will make more midrange every time. the crank trigger offset is the only thing i can think of. In the emerald we have option to swing the injector events around more so one day when i have more time i'll investigate that more.

[brogenville]

Cheers Joo- I was confident you'd come along and clear up my cloudy memory.