Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

[Donald A.]

Fellow engine Guru's

Helping my friend with his 70 LS-5 do some tuning.

Attached is the actual Cam specs of the cam used to rebuild his engine.

Can anyone comment on this cam and inform on the difference in this one verses the bone stock original cam specs for the 454, 390 horse.

Based on this analysis I'm wanting to understand what the dwell setting should be and what timing recommendations folks would have.

We are having his carb (Q-Jet) checked over for proper jets, rods etc and then want tune it out.

Without having the luxury of sending his distributor out to Lars I don't fully understand what the parameters are we should be shooting for.

Thanks for any help

[Patrick H.]

Re: Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

The replacement cam for your engine should be GM 3883986, which is this one:
http://www.cranecams.com/product/car...detail&p=23897

Yours is this one:
http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=435&sb=2

The one you now have in the engine has a lot more lift and duration. Note that Comp Cams specifically mentions that it will have a rough idle. I think you're likely going to have problems with this cam, and I would not be surprised if you "chase your tail" with this one trying to figure out whether you should tweak the carb or the distributor. Frankly, I'd change the cam.

I'm sure that Duke will give you dwell and timing comments, but I'll bet he has the same recommendation regarding the cam.

[Joe L.]

Re: Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

The replacement cam for your engine should be GM 3883986, which is this one:
http://www.cranecams.com/product/car...detail&p=23897

Yours is this one:
http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=435&sb=2

The one you now have in the engine has a lot more lift and duration. Note that Comp Cams specifically mentions that it will have a rough idle. I think you're likely going to have problems with this cam, and I would not be surprised if you "chase your tail" with this one trying to figure out whether you should tweak the carb or the distributor. Frankly, I'd change the cam.

I'm sure that Duke will give you dwell and timing comments, but I'll bet he has the same recommendation regarding the cam.

Patrick and Don------


I agree. This is not a cam that I'd use in a street engine. Some folks might; I would not.

The original L-36/LS-5 cam was one of the best cams ever devised for STREET big blocks.

[Duke W.]

Re: Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

...agree with you, Patrick. As far a the spark advance map is concerned the OP should consult with the rocket scientist that selected that cam, but he probably doesn't know what "spark advance map" means.

Alternatively, follow the guidance in my 2012 San Diego presenation for SHP (high overlap cam) and emission controlled big blocks.

The dwell angle does not need to be changed from OE spec regardless of the installed cam.

IMO there is a 20 percent chance that a lobe will go flat within the first few hundred to few thousand miles. At that point the cam will have to be changed and OE is the way to go.

I would only install a Comp Cams camshaft in an engine if it were the only cam supplier left on the planet.

This is one I don't want to get involved with.

Duke

[Duke W.]

Re: Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

Patrick and Don------



The original L-36/LS-5 cam was one of the best cams ever devised for STREET big blocks.

Absolutely!!!

Duke

[Tom L.]

Re: Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

Duke, I'm not trying to kick the bee hive but I'm curious. What is it that makes you say the cam lobes might flatten so quickly??

[Donald A.]

Re: Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

I appreciate the comments. I'm not completely surprised because I think many people make cam choices without knowing all the parameters.

This is is a friend of mine and he did not choose this cam. Whoever built the engine did. I've been in the car and I will say the idle is not great but it will kick you in the pants for sure. Part of what started us down this path was the fact that it seems to be running very rich on the low end. We thought we would start with the basic tuning and checking of the parameters of timing and carb.

I dont fault him. How would he know. Most are at the mercy of what a " builder" is telling you. For example on my LS-5 I've got no idea what cam is in it because the motor was rebuilt in 1990 and I got no records with the purchase.

Perhaps ps with some tuning advice we can make the best of it for now.

[Donald A.]

Re: Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

Duke. How would one gain access to your 2012 San Diego presentation??

thx

don

[Patrick H.]

Re: Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

Duke. How would one gain access to your 2012 San Diego presentation??

thx

don

Don,

Google it.

http://www.metroli.org/pdf/2012%20Nationals%20tuningseminar.pdf

[Patrick H.]

Re: Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

Perhaps ps with some tuning advice we can make the best of it for now.

Check which primary rods, jets and secondary rods are currently installed.
Be sure the secondary air valve is not opening too early.
I would highly recommend having someone run the distributor on a distributor machine and tuning the curve. Bill Clupper, Lars, Dave Fiedler and others will do this. Also verify that your vacuum canister on the distributor is actually working.
Let us know what spark plugs are currently installed. They can make a difference!

Patrick

[Duke W.]

Re: Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

Duke, I'm not trying to kick the bee hive but I'm curious. What is it that makes you say the cam lobes might flatten so quickly??

That cam has more aggressive dynamics than the OE cam, so it probably requires higher rate springs than OE, which are already pretty high. Also, various forums have more reports of Comp Cam cam failures than any other manufacturer.

They don't Parkerize their cams, although I have heard that it is "optional at extra cost". All GM cams were Parkerized as it aids break-in. Federal Mogul (Sealed Power and Spreed Pro brands) and Crane Parkerize all their cams.

My first choice in cam replacement is Federal Mogul. Crane is my second choice, and they also manufactured the custom cams I designed. They were all Parkerized and since the lobes were OE (just mixed from different OE cams with different POMLs) they only needed OE springs, which with carefully set up installed heights revved to 6500+ (hydraulic lifters).

Duke

[Donald A.]

Re: Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

Duke. You and other provide such valuable information. Thank you for this.

I understand what you said about staying away from this one but please reconsider.

Question, based on the cam we are dealing with what would you do regarding the carb jets and rods. The carbs (he has a spare that is being gone through as well) are being torn down now and we are looking close to determine the configuration.

In your opinion does the current cam mean that the stock jets/rods would not be appropriate? If so what are your thoughts? Since we have two carbs we could have one 100% stock and one with mods that may work better with this cam.

My disclaimer is that I don't really understand the relationship between cam and carbureration. Ha

[Duke W.]

Re: Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

Assuming you have the original LS-5 carb, it was set up for a lower overlap cam and emissions. The only simple adjustment is the idle mixture, and this can probably be used to get the best idle quality using the traditional non-emssion adjustment procedure.

First, get the spark advance map set up suitable for a high overlap cam big block (per the suggested starting points for a SHP big block in my San Diego presentation), disable TCS, convert to full time vacuum advance, and use the Two-Inch Rule to select a suitable VAC. Then dial in the idle speed mixture.

The OE spark advance map specs are in the CSM and AMA specs, but you have to measure on the car because it may have been modified. Once you determine the current spark advance map, you should be able to figure out what you need to do to achieve a more optimized map.

If idle mixture adjustment cannot eliminate off-idle stumble or low speed surge, a larger primary main jet will be required. The secondary metering rods should be okay.



Duke

[Donald A.]

Re: Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

Duke; Thank you for sharing your knowledge and thanks to others as well. More importantly thanks for being patient with those who are less educated. I hope you will be patient with me as I try and learn from you and others.

1. So if I follow your last post we should stay with original specs on the Q-Jet for now and concentrate on spark advance map etc.

2. His car does not have the TCS so there is no issue with that in the equation

3. "convert to full time Vacuum Advance", God I wish I knew what you meant by that. Can you explain a little bit on exactly how to do that?

4. I looked at your San Diego presentation and will do my best to interpret it, but a lot went over my head at first glance.

Thanks for the continued education. PS. I'd pay good money to hear you give that presentation!

[Donald A.]

Re: Calling Cam Guru's. Help with cam and tuning, 70 LS-5-5 454

Bump please