Author Topic: cam question  (Read 4489 times)

Offline 1979C20

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cam question
« on: December 10, 2010, 03:06:31 AM »
I rebuilt my 350, basically 100% stock. The only differences are, .030 grind on the crank journals(spun bearing) and a larger cam then stock. I went to Lopers and asked them for the biggest cam I could use with stock valve train, and they gave me a comp cams 12-206-2. Its .440 lift, 260 duration. Is that correct that its largest with stock valve train, and what would you say of the specs? I have more specs, but those seemed more important I guess. Its got a grate lope to it, and idles beautifully at 550rmps. This motor comes ALIVE. First gear pegs 38 miles an hour at 6krpm in like 3 seconds. Just MEAN for a street truck.
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline eventhorizon66

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Re: cam question
« Reply #1 on: December 10, 2010, 04:17:15 PM »
That sounds like a fine cam for a stock-ish 350.  Nice modest duration single pattern for good low-end with stock compression and plenty more lift than a stock 929 cam.  I believe that the rule of thumb for NEW stock springs is less than .450".  So that cam with 1.5:1 rockers should be OK.  Enjoy it.
'85 C10 SWB 350 700R4 TKO600

Offline 1979C20

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Re: cam question
« Reply #2 on: December 10, 2010, 04:36:11 PM »
Okay. Thanks a lot. I do enjoy it! (:

1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline 1979C20

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Re: cam question
« Reply #3 on: December 16, 2010, 10:47:26 AM »
I just looked up the part number of my cam, and I was curios.... This says the range is 5200 rpm max, Is it safe that I've revved up to 6000+ rpm?
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline TexasRed

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Re: cam question
« Reply #4 on: December 16, 2010, 11:47:29 AM »
That's the power range. You just won't be making a whole lot more power outta that range. If you've got good valve springs, you can safely rev it to wherever you want.

Offline 1979C20

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Re: cam question
« Reply #5 on: December 16, 2010, 11:58:56 AM »
OHHHHH. haha. Okay. That's a relief. I've revved it up to just over 6k, and I didnt hear the valves float or anything, But I dont want to risk going any higher. It sounds like the motor is maxing out at just above 6k. Like it doesnt want to go any faster. But these old trucks dont have rev limiters!
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline Psycho71

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Re: cam question
« Reply #6 on: December 16, 2010, 06:33:41 PM »



In my experience there's nothing to be gained by twisting a stock valvetrain above about 4800-5000rpm. It might do it, but time slips at the track have proven over and over that shifting around 4500-4700 will yield better ET's. 

Just food for thought. Results will definitely vary though.
There are two tools needed, duct tape and WD40. If it moves and shouldn't, use the duct tape. If it doesn't move and should, use the WD 40.

Offline 1979C20

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Re: cam question
« Reply #7 on: December 16, 2010, 07:04:23 PM »
Eh, I'm no professional. Its just fun to rev it up super high when I'm "racing" someone. Because, its intimidating. There are a surprising amount of "tough guys" in Mesa. So far, I've got an eclipse GTv6, a riced out Honda Civic, a lifted Dodge Cum-apart, and an old jeep under my belt. And, some other people kind of rev and screw around but dont really race. I lost to little mercury or like a volvo or something because I dropped the clutch too fast and just slammed my synchros and didn't hit second. I just like to have fun. (= Everyone has been good sports about it. Both the Dodge and the old jeep came around for seconds and thirds. Haha. All of them waved and went on their way. But, last night the jeep pulled up next to me at a light. He went fast from the light so I got up next to him, downshifted, and passed him. Next light, I got him off the line. And the third light, I drove normal. He was revving up and slamming and grinding his gears, and he got pulled over!!!! HAHAHAHAHAHA. Poor guy, but I find it hilarious. For some reason he wouldnt give up. Sorry for ranting, I just like to share. Haha.
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline fitz

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Re: cam question
« Reply #8 on: December 16, 2010, 09:10:40 PM »
Ever think of going to a track to race a real car?

Offline 78 Chevyrado

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Re: cam question
« Reply #9 on: December 16, 2010, 10:06:33 PM »
OHHHHH. haha. Okay. That's a relief. I've revved it up to just over 6k, and I didnt hear the valves float or anything,

Just remember, just because a part didn't break, doesn't mean it didn't bend.  This applies to valves, pushrods, rocker arms cranks and connecting rods.

Increasing RPM exponentionally increases loads.  for example your engine is running 2000RPM, if you double that speed to 4000RPM, you don't double the loads on the parts, you triple or quadruple the loads.
Kenny

1978 C-20, 350/400, 3.73, Graystone Metallic, Raceline Renegade 8 Wheels - 18x8.5, 275/70R18 BFG KO's

Offline eventhorizon66

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Re: cam question
« Reply #10 on: December 18, 2010, 12:11:37 PM »
I wouldn't rev it past 6000 (or 5500 for that matter) just for the heck of it.  Not if you want it to last.  Oh, and let's keep the racing on the track.  Nobody'll be having a good time when you slam into a minivan and kill 5 people.

http://www.click2houston.com/news/22467538/detail.html
« Last Edit: December 18, 2010, 12:14:33 PM by eventhorizon66 »
'85 C10 SWB 350 700R4 TKO600

Offline TexasRed

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Re: cam question
« Reply #11 on: December 18, 2010, 12:28:53 PM »
blackhole: what part of the houston area are you in, may I ask?

Offline 1979C20

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Re: cam question
« Reply #12 on: December 18, 2010, 12:52:59 PM »
Well, this has always been in the middle of the night, like 2am when there are almost no cars. And the speeds never exceed 50 in a 45 zone. I accelerate quickly to the speed limit then just cruise. And, I'm hoping to take my truck out to fire bird some day for the run what you brung. But I understand, any form of high acceleration is very dangerous in an urban area, and stupid of me to do. But I'm 17 and cocky.
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline Captkaos

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Re: cam question
« Reply #13 on: December 18, 2010, 01:16:45 PM »
Over revving is going to make you slower if you aren't making any power in that range, and a stock motor with stock springs is going to give out at about 5500, and your cam stopped at 5200...

Offline 1979C20

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Re: cam question
« Reply #14 on: December 18, 2010, 02:06:48 PM »
Well, I don't ride it out at 6k. That's just where it reaches right as I go to shift. I shift right as it runs out of power.
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF