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Discussion Starter #1
I recently installed AFR 195 eliminators and a compcams XE268H cam. I've completed the break in of 30 minutes and changed the oil. The car just doesn't seem to have the power. When feeling the exhaust pressure it is clear that there is more exhaust coming from the left bank of cylinders than the right bank. The timing was checked with a timing light and is correct. The throttle response is hesitant and slow. The car is auto, 3.08 stock gears, no stall, 600 cfm edelbrock. Feedback/advice on what I could do to get the motor performing like it should would be awesome. Thanks everyone and looking forward ti what you have to say.
 

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from the very limited info---the symtoms sound like one or both sides of the exhaust has a clogged or partly clogged catalitic converter, you might want to have that checked out. check the fuel pressure and carb out also, Id check the valve adjustment also

http://www.digitalcorvettes.com/forums/showthread.php?t=77602
 

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The cats have been removed. I also removed the 600 edelbrock and replaced it with a practically brand new q-jet that flows 750 cfm. I also put in about 5 gallons of 91 octane after the 87 that was in there was gone. I took off the valve covers and tightened down two rocker arms that came a little bit loose. On startup, the motor sounded much cleaner and idled great at about 700 rpm. The engine also revs well while in park with no hesitation. As soon as I take it down the road and open up the secondaries, the car bogs and basically dies, followed by a backfire or two. The power is no where near what it was before with stock heads and a very mild cam. Is there something wrong with my head/cam compatability? I'm completely lost.
 

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The cats have been removed. I also removed the 600 edelbrock and replaced it with a practically brand new q-jet that flows 750 cfm. I also put in about 5 gallons of 91 octane after the 87 that was in there was gone. I took off the valve covers and tightened down two rocker arms that came a little bit loose. On startup, the motor sounded much cleaner and idled great at about 700 rpm. The engine also revs well while in park with no hesitation. As soon as I take it down the road and open up the secondaries, the car bogs and basically dies, followed by a backfire or two. The power is no where near what it was before with stock heads and a very mild cam. Is there something wrong with my head/cam compatability? I'm completely lost.
I hate to say this you may have wiped lobes.

4 years ago, I installed an XE274 cam. After break-in, I also had two loose rocker arms. They weren't loose, the lobes were wiped.:down:

The XE series cams are very sensitive to proper break-in. May be worth pulling the intake and checking the lifters.
 

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Maybe it is your stall. Judging by when this camshaft really shows it's power, I would say a stall would help. I would also go back to that carb. Sounds like it is severely too rich when the secondary kicks in. A combination of both could kill your power. I would wait on Grumpy to chime in again, as he has more experience than I.
 

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The cats have been removed. I also removed the 600 edelbrock and replaced it with a practically brand new q-jet that flows 750 cfm. I also put in about 5 gallons of 91 octane after the 87 that was in there was gone. I took off the valve covers and tightened down two rocker arms that came a little bit loose. On startup, the motor sounded much cleaner and idled great at about 700 rpm. The engine also revs well while in park with no hesitation. As soon as I take it down the road and open up the secondaries, the car bogs and basically dies, followed by a backfire or two. The power is no where near what it was before with stock heads and a very mild cam. Is there something wrong with my head/cam compatability? I'm completely lost.
You may try checking the carb..do you have vac. secondaries, may be a little Vacuum leak when they want to Kick in. Check float level, make sure its all funtioning right. Little things like that with the carb, will stop your engine from running like it should.
 

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You may try checking the carb..do you have vac. secondaries, may be a little Vacuum leak when they want to Kick in. Check float level, make sure its all funtioning right. Little things like that with the carb, will stop your engine from running like it should.
IMO, it sounds lile the vacuum secondary air flapper is opening too soon, a very common problem with Qjets......you can see a small spring up under the pass side of that air flap shaft, up top the carb...maybe a flashlight and mirror...there is a set screw there that keeps the adjustment screw positioned....loosen it, with a 1/8 blade screwdriver in the adj screw....increase tension on that spring to delay opening the secondaries....
too much air too soon fuel does not atomise, and engine bogs....dies, maybe even backfire through carb....:cheers: :thumbsup:

OH, edit....be careful you don't overtighten this spring or the air flapper will be restricted from full opening, it's only about 1/2 a turn to get it right....not a whole lot....
 

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Discussion Starter #10
After a four month college haitus, I finally got a weekend to figure out what the problem with this motor was. I removed the intake manifold, rocker arms, and lifters. Two of the lifter were completely shot on cylinders 3 and 4. The faces of the two lifters were severely worn in a concave shape. The rest of the lifters appeared normal with no apparent abnormal wear. So now the plan is to yank out the wiped cam and reinstall a new one and pay extra attention to the break in so this doesn't happen again. Would the wear of only two lifters cause such effects as described above? Total lack of power?
 

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2 lobes wiped? 1 lobe will cause everything you've described. Multiply x2. Bottom line---- YES.
 

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Is there any explaination as to why the lobes that are opposite of each other, cylinders 3 and 4, were the only ones wiped? Is there something special about these lobes that needs to be taken into consideration to ensure a proper break in?
 

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Nothing special. Luck of the draw. It could have been #1 intake and #7 exhaust just as easily. They might have missed the heat treat on the cam OR the lifters a bit. Or both. Or, or , or.

At least now you know exactly what the problem is. And how to fix it. It a shame cause it's such a PITA, but it's better than the worst case.

:cheers:
 

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I hope this isn't a stupid question but if its the lifters that are bad, why replace the cam? Couldn't you get a couple of new lifters to put in there?
 

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I hope this isn't a stupid question but if its the lifters that are bad, why replace the cam? Couldn't you get a couple of new lifters to put in there?
The ONLY stupid qusetions are the ones that don't get asked.

When a cam and lifters have been run, they develop a wear pattern particular to that individual lobe. During the manufacturing process they harden both the cam and lifters. when they run, the lifter is supposed to spin in the bore, not fast, but they do turn. Now, as they run, the hardening wears and puts it's own little private pattern on both the cam lobe and the lifter. A new lifter on an old cam- the lifter will be harder than the cam and has the potential to accelerate the wear on the cam or the other way around.
And usually, it's the cam lobe that wears first and takes out both.

Even during an overhaul it's a good idea to put the lifters back on the same lobe of the cam.
 
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