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advancing cam

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advancing cam

Postby athomp » Fri Feb 11, 2011 9:07 pm

I race a pure stock 350 with a TH350 on a 1/4 mile oval. Stock lift cam - Intake 254 cam lift, 217 duration at 0.050. Exhaust 268 cam lift, 229 duration. Cam card says LSA 108 but I measured 109.5.
Maximum 6000 RPM.
Is there any advantage to advancing to cam 4 degrees?
Thanks
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Re: advancing cam

Postby cjperformance » Fri Feb 11, 2011 9:19 pm

what comp ratio and what rpm area do you want it to respond best in?
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Re: advancing cam

Postby bigjoe1 » Fri Feb 11, 2011 9:42 pm

Most Chevy engines similar to yours like the cam to be 4 to 8 degrees advanced. Try four at a time and see what happens.


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Re: advancing cam

Postby athomp » Fri Feb 11, 2011 10:02 pm

CR 8.5:1
I need it to pull best at 3000-5000 rpm

And I forgot to mention that it needs to pull 20 inches of vacuum at 600 rpm
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Re: advancing cam

Postby xanadu » Sat Feb 12, 2011 1:44 am

What is your vac. at idle now, if you don't mind me asking. And, are you running a std. intake manifold.
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Re: advancing cam

Postby ProPower engines » Sat Feb 12, 2011 1:59 am

Like Joe said go forward. I would start with 4deg that will be a big jump for a small cam. You will see an inprovement in the lower end power but depending on cam design the upper range will suffer. If you only want to see gains in the 3000-5000 range this will get you there as long as you don't run out of cam too soon
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Re: advancing cam

Postby randy331 » Sat Feb 12, 2011 9:50 am

athomp wrote:I race a pure stock 350 with a TH350 on a 1/4 mile oval. Stock lift cam - Intake 254 cam lift, 217 duration at 0.050. Exhaust 268 cam lift, 229 duration. Cam card says LSA 108 but I measured 109.5.
Maximum 6000 RPM.
Is there any advantage to advancing to cam 4 degrees?
Thanks


I'm going against the others here.
In this engine I'm gonna bet against advancing the cam.

I dynoed a 355 engine with a similar cam as yours ( a little less duration at .050 .420/.440 lift)
I tried it at 101* / 105* / and 109* the pulls were from 3000-6000 rpm.
The 109* position won hands down. made as much power at the bottom of the pull range as the other 2 positions but more up top. Really the power curve from 3000-4000 rpm was the same with all three installed positions but the latter we put the cam in the more power up top. The 109* position really helped power up at 6000. It was up 15-16HP at 6000 rpm.
I latter tried 112*, and 116* positions at the track, and the 116* position ran the best et of that combo, but I was leaving the line at 4500 rpm, so I can't say for sure what it did to power down at 3000rpm, but 116* 60' as good and ETed the best.
I should try 120*?

I read pure stock, so I'll take it the heads aren't ported, and a stock intake? When an engine is pourly feed by the indution system, IVC is the dominant valve event. If the cylinder is still filling at IVC leaving it open latter will help more than moving the other valve events hurts.

I'm betting on a 109* or latter ICL in this situation.

There's probably power in a valve job if porting isn't legal.

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Re: advancing cam

Postby ZIGGY » Sat Feb 12, 2011 1:14 pm

randy331 wrote:There's probably power in a valve job if porting isn't legal.

I agree there is worthwhile advantage in having somebody who really knows their stuff do the valve job on a stocker like this. To the point, put me with the guys who say try the advance.
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Re: advancing cam

Postby cjperformance » Mon Feb 14, 2011 4:45 am

I would be hesitant about advancing it withs that cam/comp, if you want the best rpm range to be 3k to 5k, advancing it say 4deg will make it better up to 3500 'maybe' 4k tops but it will nose over pretty fast after that. where does it nose over now/whats its strongest rpm area?

I too have had the same experience as Randy331 with small cams like this, they will almost always perform better in their upper rpm area with some retard, around -2 or -4, depending on the actual valve events. Do you know its ICL or valve event figures?
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Re: advancing cam

Postby Matt Gruber » Mon Feb 14, 2011 8:34 am

athomp wrote:I race a pure stock 350 with a TH350 on a 1/4 mile oval. Stock lift cam - Intake 254 cam lift, 217 duration at 0.050. Exhaust 268 cam lift, 229 duration. Cam card says LSA 108 but I measured 109.5.
Maximum 6000 RPM.
Is there any advantage to advancing to cam 4 degrees?
Thanks

217/229/109.5
sure reminds me of my xe262 218/224/110 in my th400 355sbc
it has 4* advance dot to dot
no doubt it could go another 4 advanced for 8 total
i'm shifting at 5700 but 6000 is no problem with a 4bbl. With just the small spread bore 2bbls hooked up, it noses over just past 5000.
the increased exhaust duration of 229 should make it rev higher so i'd say advance it 4.
randy didn't have anywhere near 229 on the exhaust, right randy?
Last edited by Matt Gruber on Mon Feb 14, 2011 8:53 am, edited 1 time in total.
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tame a lumpy cam for the street, more street hp, 14.5-18 mpg around town (was 11-14) with a fully divided dual plane, see my site:
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drive off cold 1200 rpm no stall
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Re: advancing cam

Postby athomp » Mon Feb 14, 2011 8:46 am

"where does it nose over now/whats its strongest rpm area?"

"What is your vac. at idle now, if you don't mind me asking. And, are you running a std. intake manifold"

Stock iron 2bbl intake.
I've never used this particular cam before so I don't know about the vacuum and rpm.

Thanks for the responses
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Re: advancing cam

Postby randy331 » Mon Feb 14, 2011 9:46 am

Matt Gruber wrote:
athomp wrote:I race a pure stock 350 with a TH350 on a 1/4 mile oval. Stock lift cam - Intake 254 cam lift, 217 duration at 0.050. Exhaust 268 cam lift, 229 duration. Cam card says LSA 108 but I measured 109.5.
Maximum 6000 RPM.
Is there any advantage to advancing to cam 4 degrees?
Thanks

217/229/109.5
sure reminds me of my xe262 218/224/110 in my th400 355sbc
it has 4* advance dot to dot
no doubt it could go another 4 advanced for 8 total
i'm shifting at 5700 but 6000 is no problem with a 4bbl. With just the small spread bore 2bbls hooked up, it noses over just past 5000.
the increased exhaust duration of 229 should make it rev higher so i'd say advance it 4.
randy didn't have anywhere near 229 on the exhaust, right randy?


Matt, just becasue you have your cam in 4* advanced and it will rev to 6000 doesn't mean it makes best power at that cam position unless you've tried changing it, and validated the results on the dyno or at the track, not just seat of the pants.

My cam was 204/214 @.050 at the lifter, but after trying several 1.6 rockers, and some rocker geometry changes I was getting about 211*/216* @ .050" measured at the valve. The original posters engine is likely not more than mine as measured at the valve with stock rockers.

I just went and looked at the dyno sheets again. The 15-16 hp was comparing the 105* to the 109* position. The 101* position was down on power from 4100 rpm on up compared to the 105 and 109 positions. By 5000 rpm the 101* was down 27HP compared to the 109* position. By the end of the pull (6000) the 101* was down 39 hp.

I'd lock the ignition timing out to whatever you race at(all in at idle) to get the vacuum at idle, if retarding the cam makes it too low.

Randy
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Re: advancing cam

Postby rally » Mon Feb 14, 2011 9:50 am

In drag racing terms advancing a cam helps quicker ETs. I found this out with my setup. Tired the cam both ways, i like the advance better, engine idles better and more throttle response.
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Re: advancing cam

Postby Matt Gruber » Mon Feb 14, 2011 10:39 am

randy
how about your dyno test #'s at 3000 rpm? he needs to come out of a corner faster than the competition.
i agree that a dyno test would be needed on HIS CAM to find out for sure...
thanks for your experience as i do find it interesting.
.
.
tame a lumpy cam for the street, more street hp, 14.5-18 mpg around town (was 11-14) with a fully divided dual plane, see my site:
http://community-2.webtv.net/mattgru/carb/
drive off cold 1200 rpm no stall
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Re: advancing cam

Postby randy331 » Mon Feb 14, 2011 6:54 pm

rally wrote:In drag racing terms advancing a cam helps quicker ETs. I found this out with my setup. Tired the cam both ways, i like the advance better, engine idles better and more throttle response.


What size cam? was it as small as the one athomp is running?

Randy
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