Final thoughts on driveablity and cam selection
Thread Starter
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
Seems like a lot of initial for that cam .
What did your compression end up being?
If it helps any I got some very low speed surge on mine (a carbed motor with a large solid roller) when it started getting a touch on the rich side. Take away fuel and none. Yours can be tuned out Im sure.
What did your compression end up being?
If it helps any I got some very low speed surge on mine (a carbed motor with a large solid roller) when it started getting a touch on the rich side. Take away fuel and none. Yours can be tuned out Im sure.
Does anyone know what target AFR I should be shooting for with a cold start-up? My scans say I'm landing about 10:1 target AFR at 50-deg. If I throw any more fuel at it, I'll be in the 9's. Actually, my other cars smell a bit richer at startup. I get pretty good feedback having sidepipes right below the windows!
Another consideration is IAC steps by coolant temp. Seems like too little and I could end up richer than expected or too many steps could result in leaner than expected AFR. (Maybe I should multiply the stock value by 10% to allow for the increase to a 383, then multiple porportionally for any increase vs stock "IDLE vs coolant temp".
Melting Slicks
Joined: Mar 2002
Posts: 3,108
Likes: 126
From: S.L.C. UT
I'm taking 2-deg out for tomorrow. That puts it back to 25 -- just like stock.
Does anyone know what target AFR I should be shooting for with a cold start-up? My scans say I'm landing about 10:1 target AFR at 50-deg. If I throw any more fuel at it, I'll be in the 9's. Actually, my other cars smell a bit richer at startup. I get pretty good feedback having sidepipes right below the windows!
Another consideration is IAC steps by coolant temp. Seems like too little and I could end up richer than expected or too many steps could result in leaner than expected AFR. (Maybe I should multiply the stock value by 10% to allow for the increase to a 383, then multiple porportionally for any increase vs stock "IDLE vs coolant temp".
Does anyone know what target AFR I should be shooting for with a cold start-up? My scans say I'm landing about 10:1 target AFR at 50-deg. If I throw any more fuel at it, I'll be in the 9's. Actually, my other cars smell a bit richer at startup. I get pretty good feedback having sidepipes right below the windows!
Another consideration is IAC steps by coolant temp. Seems like too little and I could end up richer than expected or too many steps could result in leaner than expected AFR. (Maybe I should multiply the stock value by 10% to allow for the increase to a 383, then multiple porportionally for any increase vs stock "IDLE vs coolant temp".
Safety Car
Joined: Oct 2008
Posts: 4,022
Likes: 30
From: Los Angeles CA
mine runs very near stoichiometric when cold, I don't think I need it richer, for what? no load so it's not hurting anything. rich; I think is just to keep it alive when cold, I'm giving it what it needs in order to warm up and no more.
driving mode is more important to me.
when i had the stick it idle the same...
if you have the extra coin, go dyno it, and see what she does on paper
driving mode is more important to me.
when i had the stick it idle the same...
if you have the extra coin, go dyno it, and see what she does on paper
Last edited by slickfx3; Mar 3, 2011 at 03:25 AM.
Pro
Joined: Aug 2009
Posts: 725
Likes: 4
From: Plano, TX
Its not easy to tune for driveability when you are using batch fire injection. With sequential injection and some aftermarket computer like accel dfi you can adjust fuel injector timing.
The reversion or "blowing of exhaust gas into the intake" is a real problem at low rpms. That is why the factory cams have like 117lsa. No one would buy a corvette if it didn't idle right and have good manners.
If you time the injectors to spray when the intake valve is closed you can virtually eliminate cam surge. No matter what you do there will always be a little bit of surge but this is the main cause.
The reversion or "blowing of exhaust gas into the intake" is a real problem at low rpms. That is why the factory cams have like 117lsa. No one would buy a corvette if it didn't idle right and have good manners.
If you time the injectors to spray when the intake valve is closed you can virtually eliminate cam surge. No matter what you do there will always be a little bit of surge but this is the main cause.
Thread Starter
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
I also know the theory for PE and a warm motor. Are you sure the same rule applied for a cold motor?
Last edited by GREGGPENN; Mar 3, 2011 at 09:45 AM.
Thread Starter
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
mine runs very near stoichiometric when cold, I don't think I need it richer, for what? no load so it's not hurting anything. rich; I think is just to keep it alive when cold, I'm giving it what it needs in order to warm up and no more.
when i had the stick it idle the same...
when i had the stick it idle the same...
Gee....I wonder why they put chokes on pre-EFI cars? Hmmm....
So Slick...How can you go from pissing all over a 230/236 cam one week to implying you are as happy as a pig in mud?
Safety Car
Joined: Oct 2008
Posts: 4,022
Likes: 30
From: Los Angeles CA
I have started cars with chokes that started OK partial vs. full choke many times. what does that mean?, AFR leaner...I gave it what it wanted.
just the facts, I am emotionless here, as in many things, there are favorable aspects and unfavorable aspects, just bc, i ONLY said it idles at XXX, does not mean I have declared forever love and allegiance. Nor was I pissing on anything, I am calm, try it....
Last edited by slickfx3; Mar 3, 2011 at 01:28 PM.
Melting Slicks
Joined: Mar 2002
Posts: 3,108
Likes: 126
From: S.L.C. UT
Yeah I know the factory runs some rich A/F ratio's. I think WOT A/F on my C6 is in the low 11's. And if you get your A/F in the low 10's or richer you will start seeing black smoke. But we know there is some power to be had leaning P.E. from the low 11's to at least 12.5. And the factory has to make them extra rich for the people who try to get 100,000 miles out of a fuel filter that is plugged up. Being rich is safe.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Safety Car
Joined: Oct 2008
Posts: 4,022
Likes: 30
From: Los Angeles CA
cruise 17-15
idle in gear 14.7
part acceleration 14.3 keeping up with traffic, normal driving, and looking at cute chicks
decel 20-17
half throttle 13.5
full throttle 12.5
kickdown on full throttle from 4th to 3rd on the 700r4, 13.5
wideband dialed in.... priceless
idle in gear 14.7
part acceleration 14.3 keeping up with traffic, normal driving, and looking at cute chicks
decel 20-17
half throttle 13.5
full throttle 12.5
kickdown on full throttle from 4th to 3rd on the 700r4, 13.5
wideband dialed in.... priceless
Thread Starter
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
Last year, I leaned my PE -- kicking and screaming. But, depending on which cell, it's 5-10% lower than stock values. As it looks, I could still lean it further before hitting "ideal" AFR for PE. I'm running in the 12-12.5 range for WOT.
I just got thru cutting fuel in half for a warm start. I also returned to the extreme advance used for factory startup (20° - APYP vs 10° - ARAP). The surge was less prevalent but it seemed more cold blooded.
Guess I'll try more rpms, more start-up fuel, and figure out whether to raise/lower the decay number (if I want to slow decay rate). I'd be shooting for a compromise of richer AFR for the 1st minute or two.
Another oddity....some target AFR for the last minute of open loop went to 16:1. Must be related to my MAP settings at the lowest values. My INT values are in the 130-134 range when less than 1g. The idea is to trim as lean as possible for idling. Of course, closed loop kicks it back up to where it's supposed to be -- stoich.
I just got thru cutting fuel in half for a warm start. I also returned to the extreme advance used for factory startup (20° - APYP vs 10° - ARAP). The surge was less prevalent but it seemed more cold blooded.
Guess I'll try more rpms, more start-up fuel, and figure out whether to raise/lower the decay number (if I want to slow decay rate). I'd be shooting for a compromise of richer AFR for the 1st minute or two.
Another oddity....some target AFR for the last minute of open loop went to 16:1. Must be related to my MAP settings at the lowest values. My INT values are in the 130-134 range when less than 1g. The idea is to trim as lean as possible for idling. Of course, closed loop kicks it back up to where it's supposed to be -- stoich.
Thread Starter
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
If not, that's one area you could improve your mpg. Did you activate your hwy mode? If not, that's another.
Though I'll be pleasantly surprised if I can get mine lower than 800rpm (with factory-like smoothness) or below 1200rpms for cold start-up, I continue to shoot for the holy grail of 17mpg with 30mpg. Right now, I'm about 15mpg with 27hwy.
But, I haven't hit warm-weather season yet. That's another difference between me and you LA guys. It get's COLD here!
Last edited by GREGGPENN; Mar 3, 2011 at 11:37 PM.
Safety Car
Joined: Oct 2008
Posts: 4,022
Likes: 30
From: Los Angeles CA
my exhaust lopes and snorts
my engine, hisses from intake
and forged pistons rattle when cold.
the compression popping into my shortie headers
roller rockers sing like a sewing machine.
I can't order drive thru fast food, thy can't hear me talk over my Corvette,
not loud, just personality.....
and you want what?
my engine, hisses from intake
and forged pistons rattle when cold.
the compression popping into my shortie headers
roller rockers sing like a sewing machine.
I can't order drive thru fast food, thy can't hear me talk over my Corvette,
not loud, just personality.....
and you want what?
Race Director
Joined: Sep 2001
Posts: 14,682
Likes: 753
From: NEwhere Ohio
The issue for me wasn't the idle quality but rather the smell of unburned fuel that stuck to my clothes.
This is with a hotcam kit on a 93 lt1 6 speed.
Noone ever told me to expect that.
And that smell was there with a pcmless tune and ed wright tune.
I was told the smell is normal
This is with a hotcam kit on a 93 lt1 6 speed.
Noone ever told me to expect that.
And that smell was there with a pcmless tune and ed wright tune.
I was told the smell is normal
Le Mans Master
Joined: Sep 2005
Posts: 6,551
Likes: 36
From: Jenks OK
Yeah I know the factory runs some rich A/F ratio's. I think WOT A/F on my C6 is in the low 11's. And if you get your A/F in the low 10's or richer you will start seeing black smoke. But we know there is some power to be had leaning P.E. from the low 11's to at least 12.5. And the factory has to make them extra rich for the people who try to get 100,000 miles out of a fuel filter that is plugged up. Being rich is safe.
Thread Starter
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
my exhaust lopes and snorts
my engine, hisses from intake
and forged pistons rattle when cold.
the compression popping into my shortie headers
roller rockers sing like a sewing machine.
I can't order drive thru fast food, thy can't hear me talk over my Corvette,
not loud, just personality.....
and you want what?
my engine, hisses from intake
and forged pistons rattle when cold.
the compression popping into my shortie headers
roller rockers sing like a sewing machine.
I can't order drive thru fast food, thy can't hear me talk over my Corvette,
not loud, just personality.....
and you want what?
Thread Starter
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
Its not easy to tune for driveability when you are using batch fire injection. With sequential injection and some aftermarket computer like accel dfi you can adjust fuel injector timing.
The reversion or "blowing of exhaust gas into the intake" is a real problem at low rpms. That is why the factory cams have like 117lsa. No one would buy a corvette if it didn't idle right and have good manners.
If you time the injectors to spray when the intake valve is closed you can virtually eliminate cam surge. No matter what you do there will always be a little bit of surge but this is the main cause.
The reversion or "blowing of exhaust gas into the intake" is a real problem at low rpms. That is why the factory cams have like 117lsa. No one would buy a corvette if it didn't idle right and have good manners.
If you time the injectors to spray when the intake valve is closed you can virtually eliminate cam surge. No matter what you do there will always be a little bit of surge but this is the main cause.
Now I get it.
I wish I'd read this before the desk-jockey at Bullet talked me out of a 114LSA. (Ron, FWIW, if I made a change, I'd probably do a 210/218 with 114LSA and hotcam lift. It won't happen though.)
Be interesting if they made a sequential conversion that wasn't terribly expensive.
I guess I'll keep playing with less fuel to see what I can accomplish for cold starts. Thanks to TPI-421 and Slick for that heads-up.
Thread Starter
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
The issue for me wasn't the idle quality but rather the smell of unburned fuel that stuck to my clothes.
This is with a hotcam kit on a 93 lt1 6 speed.
Noone ever told me to expect that.
And that smell was there with a pcmless tune and ed wright tune.
I was told the smell is normal
This is with a hotcam kit on a 93 lt1 6 speed.
Noone ever told me to expect that.
And that smell was there with a pcmless tune and ed wright tune.
I was told the smell is normal
Drifting
Joined: May 2006
Posts: 1,428
Likes: 7
From: Chewelah Wa
Hmmm....interesting topic. I have a Comp XE256 flat tappet (212-218) that I was thinking of putting in my somewhat stock 85 motor. It is 110 LSA, but I do have the ability (material wise) to do a chip. I do want a fairly decent idle, and was hoping that I could do a decent tune on it. I have the 1-year 85 870 ECM, and there is very little info out there to help with a tune. I am currently running a stock BIN. I'm thinkin' maybe I should go with a 114 LSA cam. My current cam is 112, it idles "OK", but not perfectly smooth. The XE cam comes in a 112, I happened to score the 110 for 20 bucks (new in box).
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,063
From: altered state
St. Jude Donor '05
Used a Lunati 256 (213/219) in an Iroc (TPI, flat tappet also) will have to look up the lsa. It idled like a top not rough at all, great cam in a 350 tpi. Dont be concerned about a rough idle 
Thread Starter
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
No, that's not really what I'm saying. 110, 111, 112 vs 114LSA,,,it's more with its manners of finnesse I'm addressing here. Mine is just more cold blooded and lacks factory-level torque below 850 rpms. It's a bet that more LSA -- especially with 5.7 rods -- would have helped. (Note: shorter rods have an increasing affect on effective overlap. Longer rods do the opposite.)
More specifically, with only 1/4 throttle, it'll pull like one hundred clydesdales from a dead-stop. Try to finess it in/out of the gargage w/o much gas and it's a hair too easy to stall.
I'm talking a hair. IOW, you can tell it just doesn't want to stay running quite as easily as a stock cam. If I jump it up to 850 and add some advance, it gets better. If I jump it to 900 with another 50rpms of deadband, it's like driving factory chit.
Remember though...stock idle speed for a stick is 650.
It's rough enough you can tell it's not stock too. That part is no where near annoying though. I wish I'd used more split. With it's current manners, I'd take a bit more bubba-la, bubbla-la.
A single pattern cam has a different, less synchopated rythm.
More specifically, with only 1/4 throttle, it'll pull like one hundred clydesdales from a dead-stop. Try to finess it in/out of the gargage w/o much gas and it's a hair too easy to stall.
I'm talking a hair. IOW, you can tell it just doesn't want to stay running quite as easily as a stock cam. If I jump it up to 850 and add some advance, it gets better. If I jump it to 900 with another 50rpms of deadband, it's like driving factory chit.
Remember though...stock idle speed for a stick is 650.
It's rough enough you can tell it's not stock too. That part is no where near annoying though. I wish I'd used more split. With it's current manners, I'd take a bit more bubba-la, bubbla-la.
A single pattern cam has a different, less synchopated rythm.
Last edited by GREGGPENN; Mar 4, 2011 at 10:15 PM.