Steve
The output matches the modifications. Happened to speak to Brett this
afternoon and as he dynoed a z18T in late September with similar
modifications with 165rwhp your figures sound about right.
If it is pinging at 20 degrees your compression still sounds like 7.5:1 or
above. We axed the in chambers in my old motor and reduced it down to 6:1,
sat the pistons down the bore, hence the love for boost and ignition
advance. From memory on 25PSI we were still running 25 degrees advance and
still no detonation/pinging on pump super, however we did learn from the US
that 'high speed detonation' on turbo motors running large boost is
practically undetectable, so who knows. I don't know if we were lucky but
both my motor and Bretts FJ ran on pump super. I see a lot of guys on the
list running premium/optimax etc for street driving and have often asked
myself the question why, again maybe just the characteristics of the motors.
A couple of things that I am unaware of with your motor
Is the block o-ringed, if not it would be a wise investment next time you
need to rebuild?
What throttle body do you have?
Have you ran a pressure test across the intercooler to note any drop, ie.
inlet side 15psi outlet side 12psi?
What size turbo?
Forged Pistons?
If you are in Sydney we could arrange to meet as it has been a while since I
sat my arse in a 1600.
Jim
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]] On Behalf Of Steve Taylor
Sent: Tuesday, 7 November 2000 9:26
To: [EMAIL PROTECTED]
Subject: Re: Z18et Cam Timing/Power
Jim,
Im not too sure on this one, should of cc'd the head while i had it off i
know,
but b4 it was a totally standard head and the only decompressing ive done is
in
the chambers of the new head, still just a standard head gasket, can this
sortof drop in compression be achieved thru extensive chamber opening??
If so well that may be the problem im not sure. Tryed up to 20 degrees
advance
on the dyno with no increases so ive dropped it back to around 17-18 to ward
off pinging. As for the cam yeah like u and a few others have said the
standard
cam had a much better overall curve than the modified one but still made
exactly the same overall power - so it cant be blamed for the loss of power!
Umm apart from that im not too sure what to do next? Im thinking of getting
a
vernier cam gear and trying to get some horsies out of the cam timing?? Dont
know how successful this will be.
Does that sortof power seem about right for my setup?? Or is something
defintely amiss??
Cheers
Steve.
(p.s. she still hoots along anyway!:)
Jim Jones wrote:
> Steve
>
> Steve how far did you go down in compression ie. before and after. We
have
> seen many cars on the dyno lose anywhere between 20 - 50hp after they have
> decompressed the motor. As an example if you went say from 8:1 to 7.5:1
> with the same ignition settings then a loss of 20hp is possible. Did you
> screw any more advance into it after you decompressed the head, try 5
> degrees and see what the difference is.
>
> Decompressing will change the characteristics of the motor.
>
> As far as the cam, as I suggested the 'standard' cam was better overall (
> curve) than the special grinds so a portion of the loss may be
attributable
> to a change in cam?.
>
> Let me know how you go.
>
> Jim
>
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED]] On Behalf Of Steve Taylor
> Sent: Monday, 6 November 2000 6:23
> To: ozdat
> Subject: Z18et Cam Timing/Power
>
> Jim Jones might be able to throw some light on this one?? Anyway i
> recently blew the head gasket on my Z18. Its running a digi 1,
> intercooler etc and on 15psi was makin 180hp@wheels just b4 it blew....
> I rebuilt the motor with a polished, decompressed head, with heaps
> bigger ports and port matched manifolds and a new cam. Got it all up and
> running and it is now only makin around 160hp@wheels!!!! I tryed the
> standard cam and it makes the same power just with a bit better curve.
> Does anyone have any idea where all my power has gone or is hiding -
> cause id love to know!!! Can there be that much power in cam timing?
> Cause i set it to factory specs and maybe it was advanced b4 i took it
> apart?
> Sorry bout the length but im screwed if i know whats going on
> Steve.
>
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