advance cam or not?
Thread Starter
Burning Brakes
Joined: Sep 2000
Posts: 1,199
Likes: 1
From: NewCastle IN. USA
I'm going to leave it alone for now.
from the simulations I've ran, the difference isn't much. I can get more out of installing a lighter flywheel.
its more work, but the results of going from a 30lb to 15-20lb flywheel seem to be greater. I may go to another trannie while I'm at it and make better use of the power I have.
I hope.
RJ
from the simulations I've ran, the difference isn't much. I can get more out of installing a lighter flywheel.
its more work, but the results of going from a 30lb to 15-20lb flywheel seem to be greater. I may go to another trannie while I'm at it and make better use of the power I have.
I hope.
RJ
Safety Car
Joined: Jul 2001
Posts: 3,667
Likes: 0
From: TurtleCreek Twp Ohio
Cruise-In III Veteran
RJ, how are ya? My buddy EricVonHa mentioned that his TPIS ZZ9X cam had specifications that DID NOT match his cam card. When he had the cam in the block and checked the timing events.. he found that their published specs were off by 3 degrees. He also mentioned that the TPIS cam cards look strangely almost identical to CamMotion cam cards. So, I'd degree your cam justt to make sure it as "advertised". 
Thread Starter
Burning Brakes
Joined: Sep 2000
Posts: 1,199
Likes: 1
From: NewCastle IN. USA
Hi aquaman,
missed ya at the IRP event, should have shown up there was only 11 or 13 cars on the track.
I can believe Eric's cam card was off, mine is too (card says 246 duration, TPIS say's its 242 per phone call). after some of the replys I'm not sure where the thing is (advanced, 0, retarded), I'll have to get a better idea of just where it is and where it should go before trying anthing (don't want to make it worse).
RJ
missed ya at the IRP event, should have shown up there was only 11 or 13 cars on the track.
I can believe Eric's cam card was off, mine is too (card says 246 duration, TPIS say's its 242 per phone call). after some of the replys I'm not sure where the thing is (advanced, 0, retarded), I'll have to get a better idea of just where it is and where it should go before trying anthing (don't want to make it worse).
RJ
Le Mans Master
Joined: Feb 1999
Posts: 6,172
Likes: 11
From: somers, ny
Rj, my 701 is also 246. I thought 242 was pushing it a bit for my application, but 246.....was more than i wanted. It's in the car now and while it doesn't idle that bad, the overlap drives the ecm a little nuts and it smells super rich at idle. If i had to do it over again, i would look for something in the 236-242 range. 4 degrees off on both lobes is a lot IMO.
Thread Starter
Burning Brakes
Joined: Sep 2000
Posts: 1,199
Likes: 1
From: NewCastle IN. USA
ralph,
I feel the same way 246 is more than I wanted.
when I got the cam I called TPIS and ask what the deal was. they said it was a 242 and that the cam card was wrong.
I took their word for it, but it sure makes me wonder.
after running the numbers thru Desktop dyno2000 I find that most of the info on the cam card is for 246 duration except that the intake centerline should be 108.2 using the opening and closing events listed (not the 107 the card says).
I have mine idling at 1000rpm, like you said, it drives the ECM crazy at lower rpms but 1000 seems to work pretty well.
not sure if it would still idle OK with the cam retarded, so its just one more reason to leave it alone.
If I had it to do over, I'd probably have a custom cam ground.
maybe:
238dur @ .050"
less lobe seperation (108-111?)
and more lift.
it would be a trade off and the cam company would probably think I was nuts.
If you do your own prom tuning you can add some spark advance around idle and lean out the MAF tables (just a little around the idle area) to help out the richness. it won't totally go away but it does help some
I feel the same way 246 is more than I wanted.
when I got the cam I called TPIS and ask what the deal was. they said it was a 242 and that the cam card was wrong.
I took their word for it, but it sure makes me wonder.
after running the numbers thru Desktop dyno2000 I find that most of the info on the cam card is for 246 duration except that the intake centerline should be 108.2 using the opening and closing events listed (not the 107 the card says).
I have mine idling at 1000rpm, like you said, it drives the ECM crazy at lower rpms but 1000 seems to work pretty well.
not sure if it would still idle OK with the cam retarded, so its just one more reason to leave it alone.
If I had it to do over, I'd probably have a custom cam ground.
maybe:
238dur @ .050"
less lobe seperation (108-111?)
and more lift.
it would be a trade off and the cam company would probably think I was nuts.
If you do your own prom tuning you can add some spark advance around idle and lean out the MAF tables (just a little around the idle area) to help out the richness. it won't totally go away but it does help some
Le Mans Master
Joined: Feb 1999
Posts: 6,172
Likes: 11
From: somers, ny
RJ, mine actually idles pretty good...in fact it will idle down around 400 rpms without stalling...at least with this single plane intake i'm using. The superram would stall at anyhing thing below 800. The issue i have is the overlap tricking the O2 into thinking it's dead lean and then the ECM throws all the fuel it can at it. Right now i have to FP at only 40 psi...and the ECM is max'ed out at idle, but at least it's not choking me. At higher pressures, it's like a top fueler at idle. Jesse has offered to help clean up the tune a bit at idle.
My cam card showed 246/246 and that's how it degreed. I think i would have been happier if they ground their cams as they advertise them (ie 242/242).
My cam card showed 246/246 and that's how it degreed. I think i would have been happier if they ground their cams as they advertise them (ie 242/242).
Thread Starter
Burning Brakes
Joined: Sep 2000
Posts: 1,199
Likes: 1
From: NewCastle IN. USA
ralph,
one other thing that happened at lower idle rpms, the vaccume wasn't steady. it would jump up and down. that makes the fuel pressure jump also (since it uses vaccume to reduce fuel pressure). it was a never ending cycle: vaccume drops for a split second, fuel pressure goes up = O2 says rich.
vaccume goes back up, fuel pressure drops = O2 says lean.
the lean spots out number the rich spots (since higher vaccume happens more of the time) and the ecm see's it as "more lean spikes than rich spikes" so it must be lean.
that plus any reversion of air thru the MAF is seen as flow going into the motor and the ecm adds fuel again.
very hard to get it close to right.
RJ
one other thing that happened at lower idle rpms, the vaccume wasn't steady. it would jump up and down. that makes the fuel pressure jump also (since it uses vaccume to reduce fuel pressure). it was a never ending cycle: vaccume drops for a split second, fuel pressure goes up = O2 says rich.
vaccume goes back up, fuel pressure drops = O2 says lean.
the lean spots out number the rich spots (since higher vaccume happens more of the time) and the ecm see's it as "more lean spikes than rich spikes" so it must be lean.
that plus any reversion of air thru the MAF is seen as flow going into the motor and the ecm adds fuel again.
very hard to get it close to right.
RJ
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Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Try increasing your minimum idle speed. Besides the vacuum/fuel pressure cycle, you probably have a similar, idle speed/IAC, cycle. As the idle spreed goes up, the IAC closes to reduce it. When the idle speed starts to drop, the IAC opens to keep it up. Ski-dwn-it described it as an, "idle death spiral", finally resulting in the engine stalling. In his case, I believe he plugged the IAC passages and he idles his engine off of throttle plate opening. What you are describing is pretty much the same thing, plus the fuel pressure/mixture as an added aggravating factor. SOME IAC action is desirable, if an idle can be maintained, for cold starts and A/C operation.
RACE ON!!!
RACE ON!!!
Last edited by CFI-EFI; Aug 5, 2004 at 10:42 AM.
