MC tweaks

[Nate Stuart]

Cody said:
> I have a few questions about simple tweaks for power on an MC engine in a
> '87 5ktq. I'm not quite satisfied with the power I have in the EFI car (I
> highly doubt I EVER will be satisfied no matter how much it has), but I
> can't spend the cash for the T3/T4 and header right now, so I'm wondering
> what more I can do to get a bit more out of it with what I have.

The hill only gets steeper at this point, you've already conqured the
fueling issue, now it's down to ignition, airflow, and airflow.

> First thought is I remember somebody mentioning porting the collector of
> the stock header. Whats the full story there? As far as the rest of the
> exaust I'm running no cat and I removed the rear muffler.
> The biggest issue I see now with the stock turbo is that it just can't
> match the flow I'm requesting from it. With the boost set at 2.4bar
> absolute I get great mid range power, but after about 3000rpm the boost
> starts to drop until arround 4500rpm it levels off at 2.0bar. I have heard
> of people porting thier turbos, but my thoughts on that go with the
> compressor is supposed to have a very specific clearance at the inlet and
> porting would mess with that. I fully understand that my biggest
> restriction right now is the stock EM and turbo, but like I said I can't
> afford to change them right now.

I think the EM is where most of your restrictions are hiding (mine too).
Just cant stuff enough air through it fast enough, a bigger turbo will
help, but the problem is still there, and may be in a different form with
a larger turbo. You may never reach 'peak boost' until way high in the rev
range, your boost will keep on climbing, however it may never plateau like
it's supposed to, and can, with a proper header.

> I was thinking of checking out the specs
> on 944 turbos, I have a bunch of them laying arround. I also have a
> k26/k27 hybrid, but last time I tried to fit it I found that it hits the
> alternator. Maybe I'll try that again with a smaller alt belt now that I
> think of it.

If you've got the turbos to swap around go for it, report back with the
results. I've got the same boost taper, and I'm pretty sure it's the
manifold thats my biggest problem, but the V8tt is the next step for me,
so the 'development' of my I5 has reached it's end. Still for the little
money thats in this motor, and the fact that the engine is mechanically
bone stock the power that I'm getting from it now is phenomenol. :)

> I plan on porting a head to put on it this week, and matching the intake
> manifold to the ports, but I don't expect much from that. I think I havfe
> an adjustable cam puley (it's for a 924, not sure if its the same, I'll
> look today) so I may tweak the cam a touch. Are there any other tricks for
> these motors, or any other suggestions?

You'll probably gain a little from each of those, the ingition timing may
be your next place to look for a little more power, once I went to the
programmable ignition it was quite clear that there was some conservation
in the stock MC maps, they work well, but there is more to be had with
some more aggressive timing (especially at high boost levels). Wont get
you more boost anywhere probably, but you'll have some more grunt at the
same boost.

HTH, and let us know how she goes!
-Nate
'89 90tq
'88 90q
http://www.newtsplace.com/90tq