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Home > Help Needed / General Tech Chat > 12G295 and N/A Metro Cam

dan187

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Wootton Bassett

9th Jan, 2011 at 03:07:47pm

I've just changed the head and cam on my 998 turbo to a 12G295 and a N/A metro cam.
(for info of the build before see the link below)


Trouble is it now lacks any power off boost and seems hardly any different on boost. It's been on the rollers to sort out fuelling and this is pretty spot on now. So i'm a bit confused.

Any ideas?

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

wil_h

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Betwix Harrogate and York

9th Jan, 2011 at 03:47:16pm

Is the CR the same or lower?

What have you timed the cam in at?

What rocker gaps have you set?

When dis boost arrive before, and what now?

That turbo?

Fastest 998 mini in the world? 13.05 1/4 mile 106mph



On 2nd Jan, 2013 fastcarl said:
the design shows a distinct lack of imagination,
talk about starting off with a clean sheet of paper, then not bothering to fucking draw on it,lol

On 20th Apr, 2012 Paul S said:
I'm mainly concerned about swirl in the runners caused by the tangential entry.


dan187

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Wootton Bassett

9th Jan, 2011 at 06:02:00pm

Thanks for reply.

CR is lower (28cc chambers now instead of 24)

Cam was timed using the dots. I have no other way to do it and don't have a variable timing wheel.

rocker gap set at 0.32mm

boost in before by 3500 now nearer 4000rpm

Renault 5 T2



I think the problem may be related to the ignition timing. I imagine the off boost timing of my new setup will be quite different to the previous one.

The thing is I'm having trouble with the megasquirt. It's not using the spark timing i set in it's tables but seems to be using its own values and im not sure where it is taking them from.

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

wil_h

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Betwix Harrogate and York

9th Jan, 2011 at 06:22:32pm

Increasing the cc by 4 will lower the CR by around 1 (from 9:1 to 8:1 for example). This would definately affect the boost threshold.

from my experience of a T2, the 3500 sounds about right with 9:1 CR.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph



On 2nd Jan, 2013 fastcarl said:
the design shows a distinct lack of imagination,
talk about starting off with a clean sheet of paper, then not bothering to fucking draw on it,lol

On 20th Apr, 2012 Paul S said:
I'm mainly concerned about swirl in the runners caused by the tangential entry.


theoneeyedlizard

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The Boom Boom speaker Police!

Essex

9th Jan, 2011 at 06:27:47pm

Time to turn the boost up?

In the 13's at last!.. Just

dan187

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Wootton Bassett

9th Jan, 2011 at 07:23:30pm

The biggest problem i'm having is the lack of off boost power from idle to 3500 rpm.

The car has no beans at all untill boosting.

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

dan187

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Wootton Bassett

9th Jan, 2011 at 09:52:59pm

problem mostly solved. It was megasquirt at fault. somehow it was running Alpha-N (TPS) not speed density. I'm sure it used to be right.

I had the fuelling sorted on a rolling road on friday (which is where i found out megasquirt didn't adjust the spark timing).

Presumably megasquirt was basically running fixed advance across the range.

The fuelling should still be pretty much the same now though shouldn't it?

Edited by dan187 on 9th Jan, 2011.

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo
Home > Help Needed / General Tech Chat > 12G295 and N/A Metro Cam
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