Beat that dead horse again! clarification PLUS new question

[Marteney, Steven J.]

I'm very interested in comments to Brent's response below.  I too have done
a lot of reading on TPI's but haven't got too play much, that comes in
another week or so when the engine comes back from the shop.

My understanding was that the TPIs only flowed good until about 5300 rpm,
but the cutoff shouldn't be like a switch.  You're seriously compromising
power output potential by setting up a combination that makes peak HP above
this range.  I think the 5300rpm figure is where the runners resonate and
flow best, but duration is also key in that determination.  Need to find my
equations for that :-)

I'm curious if anyone is running the stock ECM ('89 Firebird L98, or rather
B2L) with GM's ZZ3 cam (208/221 @ 050, 474/510 lift, 112 LSA) as well as the
stock TPI induction.  I'm wondering if this combination will at lest be
driveable until I can get into learning ECMs.  Also has 10.2:1 compression,
up from 9.4:1 stock.  Any comments?
Steve


-----Original Message-----
From: Brent Obermiller [mailto:ober_b at sssnet.com]
Sent: Saturday, October 30, 1999 1:19 PM
To: gmecm at efi332.eng.ohio-state.edu
Subject: Re: Hello/Beat that dead horse again! clarification




BluVette wrote:
> 
> OK guys, let me reword the original message and clear up a few points
along
> the way.
> 
> I designed and built and engine. I designed the cam. ACCORDING tot he CAM
> GRINDER and HIS computer, that cam is good for 600-650 HP, with all other
> factors taken into consideration such as heads and the rest of the
> modifications done. *I* limited the engine with 30# injectors, so if there
> was any possibility of the stock computer, with a chip in it that has
> already been modified for the supercharger.  I'm a mechanic, not an
> electronics engineer. Please, whenever possible, put your replies into
> laymens terms, and that would help a bunch!  :o) Thanks.
> Now, back to my original problem. When the engine hits 5400 rpms, it just
> stops. I was told on another list that the computer limits the rpm's at
5400
> on a stock L-98 enine in 1989. BEFORE the modifications, with only the
> supercharger, it did the same thing. I really need to spin this engine up
to
> at least 6000....so, does the computer limit the rpm's at 5400 or is
> something else doing it?  It did it with the old stock injectors, and i
> would have thought that the engine would lean out at a higher rpm with the
> new 30# injectors.
> Next problem is the idle. It is hunting between 500-700 rpms. The cam is
on
> the radical side, along with custom made full roller 1.6:1 rockers. I HAVE
> to raise the idle up to about 800-850 rpms, as it dies right now when
coming
> to a stop about 1/2 the time, especially when the engine has been running
at
> WOT, and then letting off the gas, it dies almost immedatly.
> I am sure that there are other factors to take into consideration that I
may
> not be aware of as of yet. The engine is also equiped with water/alcohol
> injection, just ahead of the throttle body to help eliminate detonation,
and
> that combined with the lowered compression ratio has done a GREAT job, and
> no knock or detonation is apparent, even under full boost conditions, so I
> don't *think* that the advance curves need to be played with any more than
> they may have already been altered by the custom chip that is already in
> place.
> 
> Someone on the list suggested swapping out the computer with one from a
> turbo GM car. Good idea, but, just HOW would I go about this, and is it
> compatable with an 89 Corvette onboard systems already in place?
> 
> Inquiring minds want to know :o)
> 
> Thanks to everyon that has been involved in this thread to this point,
> pleasae be patient and I will get up to speed.   TIA!
> -Barrett
> SCAR Corvette & Performance
> 1010 W. Hwy 131, Clarksville, IN  47129
> (812) 941-0839
> bluvette at scarcorvette.com
> www.scarcorvette.com


I read somewhere that the Tuned Port intake is only good for a certain
rpm range (5300rpm being the top).  The runners are something like 22"
long.  Also the air box volume is supposed to limit the rpm's of an
engine.  Have you considered the Accel box intake?  If I'm way off here,
help me, I'm a TBI person and have only read a lot about TPI. 

-Brent
 "A little knowledge is a dangerous thing"