The camaro has been idling real rough lately so I put a vacum gauge on it's only pulling 8-9hg. The engine is a brand new L98 with ported heads, TPIS intake, ASM runners, ported plenum, edel headers, compcams XE274H (specs to follow), and a bunch of other goodies.

cam specs:

GVL: .480 /.490
Lobe Lift: .325 / .3270
DUR @ .050: 230 / 236
LSA: 110*

The car runs but just barely, plesae help!! Thanks

Jim


[This message has been edited by camaroguy99 (edited August 16, 2001).]

 

What's your compression like? Longshot here but hows vaccuum modulator? This could be leaking air into intake and causing rough idle. Any smoke at all? Are any plugs oil fouled?

 

Thats not a ridiculusly low reading for a cam that size. Maybe even right on. My cam is just a bit bigger than that..but with a 114LSA, and I only pull 10-11".

I know a guy with a very similar cam, but a 106LSA I think it was...and he only pulled 7" of vacuum.


What do you have for ECM/PROM?

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"American made baby. 100% American iron. The muscle among the masses. My hero. Yep, you can take your ergonomically designed, space age, computer controlled, 4 door, cup holding map lighted split double wishbone split fold down retractable cargo covered moon roof piece of transportation and keep it. For I have felt the thunder. And I know the difference!"
JSP Motorsports
ICON Motorsports

 

whats "vacum modulator"? I haven't heard that term before.

other info I should have included:

It's pulling like 15-16hg at 2750 RPM. Is that what you mean by

I have an Ed Write custom chip, oh and it's a SD system.

I took the car out for a short drive and The brakes barely work.

also, it sputters stalls out if you don't keep it above 1000RPM.

So this might be normal? Should I look into getting a vacum canister? Thanks guys keep it comming.

[This message has been edited by camaroguy99 (edited August 16, 2001).]

 

I used to have that cam, but mine was in a carbed 400 in front of a T-5. I had somewhat more vacuum than that, no problem with brakes, and it idled at 700-750.

It sounds to me like you need some more fuel and/or timing at idle. Talk to chip man and see what he can do for you.

You might even want to consider getting into burning your own PROMs.

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"So many Mustangs, so little time..."
ICON Motorsports

 

I have pleantly of fuel. SVO 24lb injectors set at 48 psi. Timming has been a bitch to get down. No matter what we do it doesn't want to smooth out.

I've thought about burning my own proms but I really don't have the time with school comming up soon.

 

It doesn't matter what injectors or pressure you've got if the duty cycle is too low which is what I am suspecting is the case. That's controlled by the chip.

That's alot of cam (duration) for a TPI with its LS that low. It's not going to be easy to get it to run right.

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"So many Mustangs, so little time..."
ICON Motorsports

 

Should I consider taking it to a spped shop and letting them go for it?

Why would they make duty cycle so low if that would cause drivability problems? Is there any way I can get it running temporarily by rasing the pressure some more or doing something else?

 

You should be in the neighborhood given the vac at a higher rpm

 

That's a function of your custom chip. Specifically, idle is the one area above all others that has to be customized after a cam change. I doubt a speed shop will get it right, it's a set of [arameters within the chip that's going to have to be twiddled with until it runs as good as it can (which is still going to be tough).

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"So many Mustangs, so little time..."
ICON Motorsports

 

You're right, that's way too little vacuum, even for a cam with 230 duration. You said you're having a problem with timing? Check it and make sure it's at 6* BTDC. It sounds like it might be too retarded. Or maybe you have a vacuum leak. Plug all your vacuum lines off the intake manifold one by one and see if you can find the culpret. If that doesn't change anything then run either propane gas or brake clean around the intake and TPI to see if you have a leak there.

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Michelle
92 Formula 350
91 Z28

 

alright thanks guys, it'll be at the exhaust shop all day tomarrow but I'll check all that out on sat. thanks again guys (and gals )

 

I plugged in my accel 300+ ignition box last night and that helped alot. It starts up right up now and runs noticably more smooth. Haven't had a chance to put the vacum gauge on yet but I'm optimistic.

 

Well, I finally got the car back from the exhaust shop. I haven't had time to hook up a timing gun to it but I did fiddle with the advance a little more. I really can't advance it much more without it stalling out. I also have signifigant power losses. It feels almost the same if not weaker then my old 305 TBI. What gives?

RB83L69,

what should the duty cycle be for the engine. I know you probably can't pinpoint it, but a general range would be cool thanks again.

 

Sounds like the classic "way too big" cam story. Not only is the duration high for a 350tpi, but it is on a 110 LSA. The vacuum definatly sounds right for that cam. TPI's like LSA's in the 112-114 range which improves the idle and gets along with the computer. You also need a 3,000rpm torque converter and at least 3.73 rear gears, headers, 11:1 or better compression ratio and preferably a mini-ram. Long tube runners arn't going to cut it. Even then i'd stick the cam in 4 degrees advanced.

That's a very big cam

 

I'm thinking it is way too big. It really didn't at the time but now I'm thinking thats the problem.

What would you guys recommend? I guess a cam swap is my only solution. This is turning out to be alot more trouble then it's worth. Thanks.

Let me list my other mods so you guys can get a good idea:

K&N filters
Ported plenum
ASM SSLTR
TPIS port matched base
ported stock heads (ouch)
crane 1.5 gold roller rockers
Edelbrock headers
Random cat
Borla 3" adj. cat back
power and amp pulleys
1800 stall converter
Ed Write custom chip

I took a look a compcams web site and I think these might be better choises:

XE262H

Dur @ .050: 218/224
Lift: .464/.470
LSA: 114

XE268H

Dur @ .050: 224/230
Lift: .479/.480
LSA 114

what do ya think?

[This message has been edited by camaroguy99 (edited August 20, 2001).]

 

If you have any faith in Lingenfelter and TPIS you might consider a cam with specs close to theirs. Especially since you have a 1800rpm stall speed.

ZZ9
212/226 @ .050, .483/.520 w/1.5 rockers

74211
211/219 @ .050. .499/.525 w/1.5 rockers

 

I'd go with that one..sounds like a good cam for you.

You will still probably need a custom prom for it.

------------------
"American made baby. 100% American iron. The muscle among the masses. My hero. Yep, you can take your ergonomically designed, space age, computer controlled, 4 door, cup holding map lighted split double wishbone split fold down retractable cargo covered moon roof piece of transportation and keep it. For I have felt the thunder. And I know the difference!"
JSP Motorsports
ICON Motorsports

[This message has been edited by Jester (edited August 20, 2001).]

 

brent,

I don't think my springs will support that exh. lift. Thanks though.

I think I will end up going with the XE262H, but I would still like some more opinions.

 

The saga continues... I just pulled the engine and replaced the cam with the one above along with a 2800 stall vigilante converter. It has a little more power but is still no where near the expectations for the engine. It still feels weaker then my old 305 TBI. The vacum problem has been fixed. It ides very nicely now. Could it be the chip? Should I have ed write take another shot with it?

 

hey camaro guy where was the vacum leak? i have the simialar problems such as no breaks all consitrated to the front and cant get idle below 1000 rpm and i still cant find the vacume leak, lol i know how you feel when you say its turning out to be not worth it

 

It turned out not to be a vacum leak, but just a really big cam for my engine. I had too much duration and losing all the vacum.

 

Please I'm desperate!! This is my daily driver and I can't have it out of commision like this!! Thanks

 

As I understand it, Speed Denisty systems are a real bear to tune properly.

Unlike MAF systems that have a range of adjustment depending on mods to the engine, a SD system is much less forgiving and needs a lot more tuning to get right.

Unfortunately, if everything on the engine is installed correctly - no vacuum leaks, valve not too tight, rings gapped and installed correctly, sensors working properly, etc. - then I can only suggest two things.

You might want to play with advancing you initial timing a bit or buy or rent a Diacom program, hook it up and log some actual data that Ed can use to adjust his PROM settings.

If you don't want to go to the expense of buying the program, I believe you can rent it from TPIS.

Ed will need the data though, in order to see what's actually going on in the engine.

Hope this helps.

Jake

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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9, TPIS Long Tube Headers and DynoMax Super Turbos (HATE 'em)