Cam Choice for carb motor
TECH Fanatic
Joined: Jun 2002
Posts: 1,979
Likes: 3
From: Upstate NY
Hey, I am planning my motor build and need advice on the cam. It will be a stock bottom end 6.0, L92 heads, GMPP intake and an 850 carb. I want to run the biggest cam possible on the street. It will be paired with a TH400. Any advice?
Going in '68 Chevy truck, weight 3700, street/strip use, keeping the coils, MSD ignition controller. 3:73 gear set, looking at running a 750 or 850 Demon carb
Could I call a company like COMP and ask them to recommend one?
How easy/expensive would it be to upgrade the springs to handle a bigger cam?
No not wanting to go through fly cutting and all, thanks for the recommendation. Where should I look for a cam with those specs? Oh and I will be running headers and straight through mufflers, so no restriction there.
And thanks for the heads up on the carb size, I was just gonna see what I could buy used for cheap, either size is fine with me, although I think 650 might be a touch small, JMO
I sent an email to Futral, I like the looks of their products.
Ok, thanks for the heads up, I might need to look into deeper gears, eventually. I read that article and thought it was very cool. How high of a stall can I go with it still being streetable?
Will the stall be based on the power band and HP/TQ numbers my motor produces?
So then I should wait til I dyno the motor before choosing a converter
How about either of the three COMP THUMPR series? Would one of them fit well?
Going in '68 Chevy truck, weight 3700, street/strip use, keeping the coils, MSD ignition controller. 3:73 gear set, looking at running a 750 or 850 Demon carb
Could I call a company like COMP and ask them to recommend one?
How easy/expensive would it be to upgrade the springs to handle a bigger cam?
No not wanting to go through fly cutting and all, thanks for the recommendation. Where should I look for a cam with those specs? Oh and I will be running headers and straight through mufflers, so no restriction there.
And thanks for the heads up on the carb size, I was just gonna see what I could buy used for cheap, either size is fine with me, although I think 650 might be a touch small, JMO
I sent an email to Futral, I like the looks of their products.
Ok, thanks for the heads up, I might need to look into deeper gears, eventually. I read that article and thought it was very cool. How high of a stall can I go with it still being streetable?
Will the stall be based on the power band and HP/TQ numbers my motor produces?
So then I should wait til I dyno the motor before choosing a converter
How about either of the three COMP THUMPR series? Would one of them fit well?
What did Futral and/or Comp suggest?
I accept all advice bro. I was just answering questions about if I wanted to flycut, what size carb I wanted to run, what type of exhaust I am running, etc. Futral hasn't replied to my email. I haven't talked to Comp yet. I was just looking for answers here, do you know if the Comp Thumpr series work well in LS motors? I would really appreciate your help
I believe thunderracing.com allows you to spec your own cam. Off the shelf cams arent always the best for EFI motors even though they are designed for them. The carb motor is going to do better with a custom grind. PM PatrickG or PredatorZ for them to spec you a cam. You'll make power with any cam you put in there, just not optimal power.
TECH Fanatic
Joined: Jun 2002
Posts: 1,979
Likes: 3
From: Upstate NY
I accept all advice bro. I was just answering questions about if I wanted to flycut, what size carb I wanted to run, what type of exhaust I am running, etc. Futral hasn't replied to my email. I haven't talked to Comp yet. I was just looking for answers here, do you know if the Comp Thumpr series work well in LS motors? I would really appreciate your help
Choosing the correct designer is a big problem. Second-guessing him is a even bigger problem.
Jon
and on the converter, it would be better to have it on the engine stand rather than through a converter at the wheels.
find out the cam specs, and then any converter shop can build you a converter that will get close off of weight, duration of cam, rear end gear, etc.
sometimes its off 500 or so rpm but calculations and real world are different in some cases. im not sure if anyone still offers this policy, but it used to be one free re-stall within a 30-90 day period of purchase.
TECH Fanatic
Joined: Jun 2002
Posts: 1,979
Likes: 3
From: Upstate NY
No offense intended, but ask whomever you choose how many carbed 6L L92 engines he has done and the results from the owners. This isn't just your average LS cam picking game.
Good luck!
Jon
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TECH Fanatic
Joined: Jun 2002
Posts: 1,979
Likes: 3
From: Upstate NY
He very well may not want to give out any of the cam specs (or is asked not to!). That is his perogative if he wants to or not! I don't need to pay for any cam specs, I spec my own cams out for myself. I already have R&D work with the L92 heads and cam design (Yes, I have some very different ideas than what is found on this web site). And no one cam designer is going to have the exact same thoughts on the subject (similar but not the same) as you well know! If they did everyone would just recommend off of the shelf grinds. Personally, I think that the OP is making some big mistakes by ignoring the bottom end of the engine
TECH Fanatic
Joined: Jun 2002
Posts: 1,979
Likes: 3
From: Upstate NY
He very well may not want to give out any of the cam specs (or is asked not to!). That is his perogative if he wants to or not! I don't need to pay for any cam specs, I spec my own cams out for myself. I already have R&D work with the L92 heads and cam design (Yes, I have some very different ideas than what is found on this web site). And no one cam designer is going to have the exact same thoughts on the subject (similar but not the same) as you well know! If they did everyone would just recommend off of the shelf grinds. Personally, I think that the OP is making some big mistakes by ignoring the bottom end of the engine
FWIW, some cam guys' ideas are not even close to what I regularly see in L92 cams, especially here. That shouldn't surprise you too much.
Jon
Sorry Jon, I'm not a site sponsor and I don't use a cam company that is a site sponsor to boot. But if you want me to give you a cam profile I will. Just PM me your application, engine particulars, gear ratio used, trans type ( if AT, what stall & converter fin configuration used), tire size (brand & type as well), & type of rear axle used. You can post my return info up as well if you would like too, b/c " I just don't give a Cluck". I've got along with your son (trust me I haven't borrowed any of his ideas, but I could have if I would have wanted too!) on this forum in the past and always liked reading your posts as well.
Shane
Shane
[QUOTE=Personally, I think that the OP is making some big mistakes by ignoring the bottom end of the engine[/QUOTE]
Why? This is a budget build, with stock L92 heads. If I blow up the motor than its just a good excuse to build a forged stroker.
Why? This is a budget build, with stock L92 heads. If I blow up the motor than its just a good excuse to build a forged stroker.
Things would work with FI, but carb setups need different cam specs and you need more intake duration. Plus there are other safe guards within FI apps that you will now have to do manually. The hyperutectic piston's used by GM will not tolerate detonation very well. At the very least you should fly cut the pistons to insure your PTVC's are adequate. I also would use some aftermarket rods to insure reliability, as I have seen alot of the powder metal rods break about 1" down from the wrist pin when the rod ratings have been exceeded. Scat makes a good 4340 forged I-beam rod that won't break the bank. I like forged pistons as well as they can handle alot more abuse. The crank should be just fine as is. I would just save my money a little bit longer and do things so that they can last and provide years of enjoyment, but to each our own.
Ok, I totally understand where your coming from and I think it is very good advice, but I am going to be stubborn. I want to get the truck back up and driving, as I lose interest quickly when it sits in the garage torn apart. I will check into the rods, maybe even pistons, because it shouldn't be much work to replace those right? Especially if I already have the motor torn down.
Last edited by 1997bird; Jan 5, 2009 at 01:31 AM.