I've been told that with a stock computer I can't put a cam in my car with more than a 220 duration and the LSA has to be 112 or 114!! My question I guess is this...... if I burn a custom chip can I use a cam with a larger duration and a 110 LSA???? Specifically, a cam with the following specs...... .462/.469 lift with a 218/224 duration and a 110 LSA!!! I'm not so much worried about the duration as I am the 110 LSA! On a different note, I don't understand what I've heard about the LSA needing to be 112 or 114 considering my '86 TPI Trans Am has a stock cam with a 108 LSA from what I've read!! Any insight on the cam and the LSA would be greatly appreciated!

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1986 Trans AM
305 TPI
4 Wheel Discs
9 bolt Borg Warner Rear
Completely Stock
Soon to upgrade to a 383 stroker w/TPI, Hedman Shorty Headers, 64cc Pocket Ported Worlds Product Sportsman-II heads, ported intake, comp cam, TPIS air foil, Adjustable Fuel Pressure Regulator, and 24 lb/hr SVO injectors!
Current project: Keeping my car running until I get the money for the above mentioned project! :-)

[This message has been edited by 86TpiTransAm (edited February 05, 2001).]

 

This is gonna be short... your car will start, run and drive just FINE with that cam. The only thing you probably wont feel is the improvement you would expect at WOT. That's where a custom chip comes in.

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92 Z28 L98 350
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Ported stock heads, XR270HR-10 cam, TES headers, Crane AFPR, Flowmaster catback, MSD ignition components, #24 SVO injectors.
Best ET 13.3@107 mph
"Take that auto, drop it in first, hold the brakes, stomp the gas and grin from ear to ear! :-)
Click here to see my car at Truspeed.org

Check out TruSpeed at http://www.truspeed.org
Check out the Bin Archive at http://www.truspeed.org/bins.html

 

What about vacuum ie, power brakes with that much duration? Also, running a stock TC on AOD tranny?

 

I agree with Blade. I am running a 218/218, .503/.503 lift, 110 LSA just fine with my stock ECM. I am now looking at fine tuning the chip for best performance. Vacuum stuff works great, I just raised the idle speed about 200rpm's cuz it was a little too choppy for me.

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1989 IROC-Z 5.7L

 

While folks worry about the overlap for rpm range is has alot to do with reversion, and self egr. Also, a big role in Turbo motors in the sense of self egr since so much back pressure when under boost (some applications). What's also just as important is the actual intake valve closing point since this has a ton to do with actual dynamic compression ratio of the engine
just saying there are more issues then just LSA @50 specs lift.
If some says their Green Racer 280 cam works, then that would be the one to use since there are so many variables, and if you go too far reversion can really screw up a MAF sensor ability to read right

 

IMHO - that cam needs a custom chip for more than just the WOT. With my 218/224 Xtreme cam on a 112 my BLMs were 108 at idle. Cold starting was rough. With a 110LSA you will even less vacuum which means you'll be running more fuel pressure at the rail. Can't go lower than 108BLMs. Not really a big problem once you are in closed loop ... but, the open loop will be rough. Workable? Probably ... but definitely rough until you hit closed loop. Plus, I still have my doubts about the BLMs ... might need to go even lower than 108 which isn't possible.

Tim

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• Program your own PROMs!. Read my article to get started!
• Research and Experiment before asking questions.
• This is not a chip store. Go to the classifieds if you want someone to sell you a chip or give you a BIN.

TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

Traxion is right about the lower limits of the stock eprom won't go below 108 on the BLM. The lowest INT is 80 while the BLM is 108.

When the weather got down to -18*C (around 0*F) and I had my stock eprom with a relocated MAT I was down to INT values of 90 with a BLM of 108 due to the serious overrich condition. When I locked the BLM to 128 to begin my initial tweaking of the eprom, I immediately hit an INT of 80 and got an SES code 45 - O2 rich condition.

So I would say that agree that to get a reasonable idle when first started (the ecm is in open loop for 3-5 minutes), you should tweak the eprom accordingly to reduce this overly rich situation. I would hate to see what would happen in very cold weather. Something us "northern boys" have to contend with.

 

TRAXION....you've got mail!

 

I'm still confused! You say that a 110 LSA will cause LESS vacuum and that'll mess with the BLM's and most likely screw up my cold start idle!! I've read that my stock cam has a 108 LSA!! So wouldn't a 108 LSA cause even less vacuum than a 110 LSA???? HELP!


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1986 Trans AM
305 TPI
4 Wheel Discs
9 bolt Borg Warner Rear
Completely Stock
Soon to upgrade to a 383 stroker w/TPI, Headman Shorty Headers, AFR 190cc Heads, ported intake, comp cam, TPIS air foil, Adjustable Fuel Pressure Regulator (probably Holley), 24 lb/hr SVO injectors, and some sort of aftermarket ignition (undecided)!
Current project: Keeping my car running until I get the money for the above mentioned project! :-)

 

I think the issue is mainly lobe overlap. Overlap is a product of lobe separation AND duration. Since your stk cam has very little duration the overlap is minimal and vacuum is higher.

Generally, more duration for the same lobe separation will make less vacuum at idle due to the increased overlap.

 

Thanks Brent! I appreciate you clearing that up for me! It's makes perfect sense to me now! Reading the articles in the Comp Cam catalog helped too....thanks TRAX!

------------------
1986 Trans AM
305 TPI
4 Wheel Discs
9 bolt Borg Warner Rear
Completely Stock
Soon to upgrade to a 383 stroker w/TPI, Headman Shorty Headers, AFR 190cc Heads, ported intake, comp cam, TPIS air foil, Adjustable Fuel Pressure Regulator (probably Holley), 24 lb/hr SVO injectors, and some sort of aftermarket ignition (undecided)!
Current project: Keeping my car running until I get the money for the above mentioned project! :-)

 

Might be easiest to think of it in different terms.

Overlap is when both in and ex valves are open, when they are both open there is exhuast backpressure forcing some exhuast back into the chamber, and intake tract. This is known as self EGRing. When at operating speed and on the cam th effects are min, at idle and low speeds thou is a headache. Often using a far amount of timing will help fire this **diluted** (diluted by exhuast gases) AF mixture. Snooth idle with a big cam can be done, but can take more time then the WOT stuff.

Some calibrations allow for th option of O/L idle. Might check for that.