Waddia Think?????? - Team Camaro Tech
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post #1 of 26 (permalink) Old Jul 15th, 03, 10:22 AM Thread Starter
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A friend of mine called me with a problem and asked for my help with his 81 Corvette. He has a mildly modified 350 in it that was recently rebuilt with flat top pistons, about 10:1 compression and a mild cam. He had the bottom end done at a local engine shop and he finished the engine off himself. Cam and related parts were installed by him. Some of the mods are #186 double hump 2.02 heads. A MSD distributor with 6AL box and a Blaster SS coil, and a new Demon 650 Vac sec carb. I was introduced to this at this stage and was expected to diagnose the problem of low (and I do mean LOW) power. Everything checks out. Carb is good, ignition system is good, timing is on the money. And I'm taking his word (or at least I did)on correct cam timing. (he said he aligned the marks on the gears.) I've tried everything. Moving the timing because of the possibility of a incorrect timing pointer or slipped harmonic balancer ring and just about everything else. The engine runs not too badly. The cam, (a mild cam i'm told) sounds like a top fueler at idle. I'm at a loss to find a logical problem. I did a compression test. I got a whopping 220 PSI. I suspect the cam is advanced. Normally I would just pull this thing apart and have a look but the reason I'm fishing for suggestions is because this car has had some extensive suspension and steering mods and in order to have a look at the timing chain, the motor has to come out! No room! So before I pull it, I thought I might just ask some of you guys what you think?
Thanks
Jim
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post #2 of 26 (permalink) Old Jul 16th, 03, 04:52 PM Thread Starter
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What!!!!
Nobody wanna take a whack at this???????????
Jim
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post #3 of 26 (permalink) Old Jul 16th, 03, 05:31 PM
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Question

Quote:
Originally posted by GMJim:


the problem of low (and I do mean LOW) power. .

The engine runs not too badly.

Jim
Jim, I read the post a couple of times and I guess I don't understand
[img]graemlins/clonk.gif[/img]

It sounds like it should run, but just doesn't have the expected power?

[ 07-16-2003, 08:11 PM: Message edited by: ZZ430DropTop67RS ]

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post #4 of 26 (permalink) Old Jul 16th, 03, 06:00 PM
 
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The only thing that comes to mind is that if the car still is using the OEM exhaust, maybe the cats are choking h-ll outta her??????

Will she run without the exhaust pipes on the manifolds if she is running stock stuff??

You know, kinda like a "potato up the tailpipe" thing!!

I do know a street snow plow dumb-as- plowed a bunch of cars in hard AND plugged their tailpipes b/c my daughters car was one of them!!

Boy, I wanted to pull the stupid soa--- outta his 4x4 and beat him severely about the head and neck area so he would get the point!!

Otherwise, donno, sorry. pdq67



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post #5 of 26 (permalink) Old Jul 17th, 03, 04:18 AM Thread Starter
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Sorry about the lack of info. This car has Hooker Supercomps with sidepies. It idles, but sounds like a top fueler. I guess if you've never stood next to a top fueler when it was idleing you wouldn't understand that description. It has a very heavy thumpity thump to the idle. It sounds like if you were to put it in gear and stomp on the pedal, the thing would pull the front wheels off the ground. But in reality, it's like stepping on the pedal of a car powered by a weed whacker. Well not quite that bad, but not at all near the power it should have. I think? I know what the problem is. A camshaft that has been installed with too much retarded timing will produce low compression. A cam with too much advance will do the oposite, but I've never seen one have this much compression (220 Psi) and run at all! It should have about 125 to 160 Psi. My confidence level isn't quite what it used to be. Especially because it's not my car. Things change, and memory fails. I'm having trouble trying to keep up with todays technology just to keep my daily drivers on the road. Anyway, this is a good opportunity to learn something. I'll eventually find the problem and will post it. I just thought I might toss this out for everybody to look at (misery loves company!) and see what happens. Thanks for taking a shot at it!
Jim [img]graemlins/waving.gif[/img]
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post #6 of 26 (permalink) Old Jul 17th, 03, 09:50 AM
 
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What is the rear gear ratio?? If it is overcammed its going to run like a slug. The biggest is best theory doesnt work with camshafts. I have been around top fuel cars many times and if it sounds like that your in trouble.... And plus those top fuelers arnt idleing there, thats around 3000RPM.... Its got too much cam for the engine and it will run like **** no matter what you do.

You might wanna under carb it to try to get some low end out.

I would say get a deeper gear in the rear, make sure its not a big hydralic cam, and rev the crap out of it.
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post #7 of 26 (permalink) Old Jul 17th, 03, 10:58 AM
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Quote:
Originally posted by GMJim:
Sorry about the lack of info. This car has Hooker Supercomps with sidepies.
Jim,

I'm thinking it could be those pies on the side that are causing the problems...too much weight to power. Tell your buddy to lay off the pie for a while and he'll have a real snappy ride.

Sorry, I couldn't resist.

I have heard stories of (but never seen) crank and or cam gears being mis-marked by the manufacturer, as well as cams having the pin mis-located. I suppose that's why it's a good idea to degree the cam before buttoning things up. (I don't always take my own advice here!)


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post #8 of 26 (permalink) Old Jul 18th, 03, 12:07 PM Thread Starter
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Side Pies YUK YUK! waddia want for a two fingered typist?? Thanks for the replies. It's got 3.73:1 gears and should go like stink. Oh well, we're pulling the motor anyway. There just isn't anything else to try! It's gotta be cam timing. If it isn't were going to put Vortec heads and a roller cam in it. I'll post my findings. Should have it apart by the middle of next week.
Thanks
Jim
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post #9 of 26 (permalink) Old Jul 19th, 03, 03:11 PM
 
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could you not measure valve lift with the valve cover off in relation to the harmonic marks (and deduce cam timing)? I made the mistake of advancing my cam and it ran like a turd at idle and low rpm (but sounded deadly!) and revved nice. I've also had an internal carb leak that make the idle sound super lumpy and made low rpm operation suffer. Just some ideas.
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post #10 of 26 (permalink) Old Jul 20th, 03, 11:24 AM
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Have we checked for vacuum leaks yet? That will give you a rough idle and a loss of power. You might want to look into that before puilling the engine. I also agree that if it is majorly over cammed it could be a slug at low RPM's. Does it wake up on the highway one it is at speed? I would be interested in your findings. Keep us posted.

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post #11 of 26 (permalink) Old Jul 21st, 03, 06:41 AM Thread Starter
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We checked for vacuum leaks and everything looked good. Just before we pull the motor, we're going to try to get a degree wheel in there and check cam timing. It's easier to yank the motor than try to work on it in the car.
Jim
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post #12 of 26 (permalink) Old Jul 21st, 03, 08:32 AM
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A few years back a friend of mines dad build a '73 429 ford for his truck. He put flat tops in it (about 9.0-1 with 92cc heads) and a 280 comp magnum cam. I have heard the 280 magnum before in a lot fo cars and this thing sounded more like a 305 magnum...very rough and lumpy. It also had very poor response under about 2500 rpms, but then from there on up it was like someone turned on a small nitrous hit. Turned out he put the cam in 4* advance...and the cam comes from the factory already 4* advanced, so he had 8* total advance at the cam. Seems to me it threw the cam timing out of its normal operating window. He put it in straight up on the timing gears and the difference was amazing...it still sounded good but much more in line with what it should have sounded like, and it actually pulled harder from a dead stop. Sounds like you buddies car has the same problem. How much idle vac does this thing pull?

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post #13 of 26 (permalink) Old Jul 21st, 03, 05:27 PM Thread Starter
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Vacuum is a very low 8 to 10". I'm hoping I'm right, and it is cam timing. This car is a real pain to work on. It has one of the nicest paint jobs I've ever seen. We don't want to add to the problem by scratching it up.
Jim
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post #14 of 26 (permalink) Old Jul 21st, 03, 09:29 PM
 
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a lot of the aftermarket crank sprockets have (2) "zeroes" on them, one right above the keyway/ruffridge key, and another about 10 degrees off to the left of the ruffridge key. You want to use the zero that isn't directly above the ruffridge key, that messes up the timing. My friend did the same thing, car ran okay but right at 3500 rpm's it would cut out really bad. So when you install the crank sproket and line up the dots, the zero should be straight up with the ruffridge key off to the right about 10 degrees. Maybe you could just let the tailhousing of the tranny lean down, which would make the balancer stick higher up making clearance?
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post #15 of 26 (permalink) Old Jul 22nd, 03, 04:31 AM Thread Starter
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Thanks Cody
We're going to try to fix it without removing the motor first. The tranny has to come out first anyway. So before we yank the motor we're going to try to tilt the motor back and lift it a little to get access to the balancer.
Jim
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