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Old 07-06-2009, 08:28 AM
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Disappointment with new cam/head swap

Hello,

Recently did a cam/head swap on my 350 chevy. Originally it had "487" casting heads, a 204/212 duration cam, and a performer intake with a quadrajet carb. The motor ran fine before I did the swap. The motor has flattop pistons. I put on vortec heads that have a z/28 type spring good for .550 lift. The cam I used is a comp extreme energy 218/224 duration .462/.469 lift. I used a cloyes true roller timing set that had 3 different ways to install the cam. We installed the cam "straight up" because I was told the cam already has 4 degrees advance ground into it. I used a .041 head gasket. I also put on a performer rpm intake. I am really dissappointed in the performance I am getting. In fact I think it ran better with my old setup. Currently running 12* initial advance, 32* all in by 2800 rpm. About 48* total with vacuum advance plugged in. It just seems the motor is really unresponsive for being almost 10:1 compression. Any ideas of where to start looking for where I went wrong? Thanks.

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Old 07-06-2009, 08:44 AM
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Have you tried it running with 91 octane fuel yet? Close to 10.1 compression ratios require it.
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Old 07-06-2009, 09:32 AM
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I would not use Comp Cams if they were free, UNLESS is is a custom grind, then they seem to work fine. I have have had the exact same experience as yours and ultimately it was the cam. In Fords, Chevs, and most recently a AMC. The 401 ran OK with the Comp Cam, about the same as the stock cam that it replaced, but after swapping it to a Isky, it ran like it should.
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Old 07-06-2009, 09:35 AM
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i've had trouble with comp too. that brand of cams has officially been scrapped
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Old 07-06-2009, 09:51 AM
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the gasket is probably too thick, but that is not a big enoguh issue to cause a major power loss- your timing loosk a hair too low as well. And as noted that cam may not be optimal- but shoudl still be decent. How does it do over 3,000 RPM- that is where you should notice the biggest difference.
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Old 07-06-2009, 10:26 AM
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From what you posted, you did not degree the cam. There is a chance things got messed up on install and a chance the cam gear was out some.
Did you also use a aftermarket timing pointer without establishing ture TDC on the balancer? They are famous for being pretty but inaccurate. The last one I installed was a full 4deg out.
Any and all of these oversights or a combo of, can and will cause you to get a good bit less power than what you would expect from the parts.

My old, simple, throw together 350 vortec head motor with rpm manifold and generic 214-224 .442-.465-112 cam wanted 36deg timing and ran 13 flat @105 all day every day. Picked up a full 1 sec in 1/4 mi et and 4.5 mph drag test compared to #882 heads/performer manifold on the same motor
It made a true 374 Brake Horsepower, exactly as it should. The true cr was 10.05:1 measured.
Something is definatly up. Unless the 487's were big valve and expertly ported, you should have seen a good increase in both torque and power.

What is the casting number of your vortec heads? (under the valve cover)
New, recent GM Parts heads or the origional '96 to 2000 GM OEM L-31 truck heads, or aftermarket copy?
Apparently the new/recent GM service heads are from Mexico and do not flow the same as the old OEM L-31 heads or make as much power. (typically down 20hp according to some engine builders dyno results)


Other details......
Your true cr with a .041" gasket and a .045" piston deck clearance (typical rebuilder 1.54" CH flat top pistons) can be a as low as 9.3:1 If this is the true specs of your motor, swapping to a .015" shim gasket would get you up to just a hair under 10:1 true cr.

I put my bet on a cam timing/ignition timing accuracy issue.
What vehicle is this motor in? what rear gear ratio? what transmission, converter stall speed.

Last edited by F-BIRD'88; 07-06-2009 at 10:47 AM.
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Old 07-06-2009, 12:19 PM
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Well, I'm definetely going to have to do some more investigating because I know something is wrong. The motor is in an 86 chevy 1/2 ton 4x4. I know it is heavy but it wont even think about breaking the tires loose. It has a th350 with a 3.42 rear end and stock converter. The vortec's are 906 casting #. This particular cam is spose to run in the 1300-5600 rpm range. I can't get it to climb over 4500 rpm. We did verify true TDC and marked the balancer according to that, but yes it is an aftermarket timing pointer. However, we played with the timing quite a bit with no real change in power. When hooked up to a vacuum gauge it was pulling 14 hg. The valve springs I used are spose to be good to .550 lift. Could these springs be too heavy for the cam I am using?
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Old 07-06-2009, 01:09 PM
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Quote:
Originally Posted by Chevy21
Could these springs be too heavy for the cam I am using?
The spring rate has nada to do w/the current problem.

If you are absolutely positive the ignition timing is fine, I'd suspect the cam/timing chain and gears has been installed a tooth off.
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Old 07-06-2009, 01:11 PM
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I`m curious, did you use the same Quadrajet carb when you got the performer RPM? if the performer RPM is a square bore pattern the Q-jet will bolt up but the secondary`s will not work due to it being a spread bore carb. I sure hope that`s not happened. Next is, where is the vac advance connected to? a ported or a manifold vacuum source?
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Old 07-06-2009, 01:29 PM
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This cam really doesn't get real busy until 2500+rpm. (reguardless of the advertized power range)
Althou this cam is advertized to work with a stock converter,
A high stall converter up to 3000 rpm will make a big, big difference. especially if your "stock converter" is only 1700 or less stall. Some stock converters are as low as 1300 stall.
You could use a lot more rear gear expecially with typical 4x4 tires.
3.42 is not enough gear for a a heavy truck and 32"+ tires.
Think 4.56:1 if you have tall tires.
that being said there still may be an internal engine issue.
Start with a compression test.

Possible fuel flow issue.

Last edited by F-BIRD'88; 07-06-2009 at 01:37 PM.
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Old 07-06-2009, 01:49 PM
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What is the casting number of your vortec heads? (under the valve cover)
New, recent GM Parts heads or the original '96 to 2000 GM OEM L-31 truck heads, or after market copy?
Apparently the new/recent GM service heads are from Mexico and do not flow the same as the old OEM L-31 heads or make as much power. (typically down 20hp according to some engine builders dyno results)

Hmmm I did not know this about the mexico castings, my 062 castings were from scoggin dickys and there was "assembled in mexico" in the casting? 20hp is a huge deal. I researched the hell out these heads and that info never came up before now, makes me wonder...I would like to know more about this

I have recently done the same vortec swap and have a comp XE 12-235-2 grind which is a 210/218 dur @ 0.050 with 447/462 lift and 111 lsa 4x4 cam. Also used 41 thou gasket, performer EPS with edy 1405 carb, 1 inch spacer, headers. Cam is straight up and run 12 deg initial adv, 45 total with the vac adv can, 3 spd tranny with 3.73 in a 72 C10. I am getting very good performance compared to my old 76cc heads, other than some valve train noise which I can't make go away. Also I made the mistake of not measuring the piston to deck height so I don't know the squench or the true CR. It will smoke the tires without dumping the clutch and break the tires loose when shifting hard into 2nd. There is something a-miss with your setup for sure.
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Old 07-06-2009, 02:02 PM
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Quote:
Originally Posted by Custom10
What is the casting number of your vortec heads? (under the valve cover)
New, recent GM Parts heads or the original '96 to 2000 GM OEM L-31 truck heads, or after market copy?
Apparently the new/recent GM service heads are from Mexico and do not flow the same as the old OEM L-31 heads or make as much power. (typically down 20hp according to some engine builders dyno results)

Hmmm I did not know this about the mexico castings, my 062 castings were from scoggin dickys and there was "assembled in mexico" in the casting? 20hp is a huge deal. I researched the hell out these heads and that info never came up before now, makes me wonder...I would like to know more about this

I have recently done the same vortec swap and have a comp XE 12-235-2 grind which is a 210/218 dur @ 0.050 with 447/462 lift and 111 lsa 4x4 cam. Also used 41 thou gasket, performer EPS with edy 1405 carb, 1 inch spacer, headers. Cam is straight up and run 12 deg initial adv, 45 total with the vac adv can, 3 spd tranny with 3.73 in a 72 C10. I am getting very good performance compared to my old 76cc heads, other than some valve train noise which I can't make go away. Also I made the mistake of not measuring the piston to deck height so I don't know the squench or the true CR. It will smoke the tires without dumping the clutch and break the tires loose when shifting hard into 2nd. There is something a-miss with your setup for sure.
reference: http://speedtalk.com/forum/viewtopic.php?t=15255
You have to join the forum to read in the "advanced" section this is not the first mention of the difference in the new Mex cast heads.
Joe Sherman who comments in this forum thread is a internationally recognized custom racing engine Guru (among others that hang around this forum) that hase worked quite a bit on Vortec head combos and knows his stuff.
I have not personally flow tested the new Mex heads myself but have worked with the older OEM 062's that were made here in Canada and installed on the 96 to 2000 L-31 truck engines.
They flow tested at 228cfm in stock form with stock valves.

http://www.fbparts.com/gmp%20SBC_head.htm
The data on this pages clearly shows the new vortecs (not the bowties) heads are down quite a bit.

http://www.joeshermanracing.com/
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Old 07-06-2009, 02:43 PM
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Quote:
Originally Posted by F-BIRD'88
reference: http://speedtalk.com/forum/viewtopic.php?t=15255
You have to join the forum to read in the "advanced" section this is not the first mention of the difference in the new Mex cast heads.
Joe Sherman who comments in this forum thread is a internationally recognized custom racing engine Guru (among others that hang around this forum) that hase worked quite a bit on Vortec head combos and knows his stuff.
I have not personally flow tested the new Mex heads myself but have worked with the older OEM 062's that were made here in Canada and installed on the 96 to 2000 L-31 truck engines.
They flow tested at 228cfm in stock form with stock valves.

http://www.fbparts.com/gmp%20SBC_head.htm
The data on this pages clearly shows the new vortecs (not the bowties) heads are down quite a bit.

http://www.joeshermanracing.com/
Seems that every time I am on this forum I gain some more knowledge. I would have thought that any 062 casting from 96 on would be the same. So when we are taking L-31 it means from 96-2000 only. After that (2000) a 062 casting would be the mexico head and not really a L31? Thanks F-BIRD
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Old 07-06-2009, 02:59 PM
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Quote:
Originally Posted by Custom10
Seems that every time I am on this forum I gain some more knowledge. I would have thought that any 062 casting from 96 on would be the same. So when we are taking L-31 it means from 96-2000 only. After that (2000) a 062 casting would be the mexico head and not really a L31? Thanks F-BIRD
Yes GM moved the V8 L-31 vortec head production from here in St. Catharines and moved it to Mexico right around the time the trucks started getting the New Generation LS type motors.

The apparent difference in the castings has been getting some "press".
Maybe the New GM Corporation will smarten up.

The GM Bowtie stuff seems to be pretty good thou. A lot of the typical required valvetrain upgrades are already done and the Bowtie vortec castings and ports are much better.
I like this head package PN: http://www.shopfbparts.com/servlet/Detail?no=155
Thats a mean vortec head.
Not bad pricing either.

Last edited by F-BIRD'88; 07-06-2009 at 03:04 PM.
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Old 07-06-2009, 05:29 PM
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Well shoot, I may have to go back and double check that it didnt get installed a tooth off. Although it shouldnt have because we turned the engine over to make sure that the dots on the cam and crank lined up with each other after making a revolution. Quesition: There were 3 different ways to install the cam; retarded, straight up (which I used), and advanced. Installing it advanced increases low speed torque while retarding it increases high end torque. Would it have been better to install it advanced for low speed torque in a heavy vehicle like mine?

Anyway, yeah I used the same quadrajet carb. I had to use an adapter for it though going from the spreadbore carb to squarebore intake. The adapter is the open center style. Well, I am going to do a compression test on it tonight and see what I find.
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