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I just took that car out and got some fuel in it. It has plenty of torque from 2000 to 5000. The concern I have is, the car and engine shakes so violently and erratically as the car is warming up it does not look happy, Once you hit the throttle its happy, and sounds healthy as the side pipes roar...
As I read this thread, one thing that keeps occurring to me is that there might be something else going on that is causing what you describe as the engine "shaking violently and erratically."
Even if the engine has a big cam (which has not been 100% verified), the idle should smooth out at 1000 rpm.
Before you yank the cam, I suggest that you do some basic checks on the compression, ignition, and fuel delivery. It would be a shame to go to all the trouble of replacing the cam if it turns out the problem with the idle stability is being caused by something else.
As I read this thread, one thing that keeps occurring to me is that there might be something else going on that is causing what you describe as the engine "shaking violently and erratically."
Even if the engine has a big cam (which has not been 100% verified), the idle should smooth out at 1000 rpm.
Before you yank the cam, I suggest that you do some basic checks on the compression, ignition, and fuel delivery. It would be a shame to go to all the trouble of replacing the cam if it turns out the problem with the idle stability is being caused by something else.
I would be replacing motor mounts and the trans mount (needed or not, on a new to me car that "Shakes like a *****'s in 4WD").
As I read this thread, one thing that keeps occurring to me is that there might be something else going on that is causing what you describe as the engine "shaking violently and erratically."
Even if the engine has a big cam (which has not been 100% verified), the idle should smooth out at 1000 rpm.
Before you yank the cam, I suggest that you do some basic checks on the compression, ignition, and fuel delivery. It would be a shame to go to all the trouble of replacing the cam if it turns out the problem with the idle stability is being caused by something else.
Agree, and that is exactly what I am going to do. I am going to replace the vac advance can (4V1053), pursuant to Dukes recommendation and will inspect my distributor and remap my timing advance. I don't have a choke so I may add an electric choke and then re-adjust my carb. These steps will improve idle and drive ability but I am probably still going to replace the cam since everything I have learned indicates its not the right cam for my desired driving conditions. The 108 LSA is too small which explains the choppy idle. The 65 degrees of overlap is a bit high and contributes to the low vacuum of 11 inches at idle. The 60 degree difference in intake and exhaust duration is just too much....The car smooths out once it warms up and certainly above 1000 rpm,
How do I advance he cam 4 degrees ?
I know I need a timing set with 3 keyways , but do I use the keyway at
4 o'clock or the one at 8 o'clock ?
Also , what does IPOML stand for ?
Thanks,
I recommend the truck roller chain (made by Cloyes). NAPA offers both the standard OE replacement set with one hole for the index pin and for about the same price, 30 bucks, the same set with three holes to give you the option of four degrees advance or retard.
I believe the adjustable set has instructions. In fact, there was a thread on this subject in the last couple of weeks. You should search for it.
Going back to 1957 all OE cam lobes except the Duntov are asymmetrical, so the "centerline" is not the same as the "point of maximum lift. As an engineer I don't like a lot of aftermarket "hot rod lingo" because it can be vague and confusing, especially when talking about camshafts.
Not that it means much, my friend has a low mile 66 350 HP, had it honed and new 10.1 flat top pistons, Eagle rods, Comp Cams 280 H camshaft, 3.70 gears. Pulls hard all the way to 6000 RPM. Great manners around town and will sit and idle all day long at 700 RPM. Very impressive sound through its original GM side mounted exhaust.
Mike
Does anyone know the labor charge to replace a cam?
Does the engine need to come out of the car?
The engine does not need to come out of the car, but the radiator has to come out to provide enough room to pull the cam all the way out of the engine. Components that need to be taken off the engine include the distributor, intake manifold, valve covers, fan, water pump, oil pan, harmonic damper, timing cover, and timing gear set.
I have no idea what a good shop charges to do a cam swap. Based on my own experience doing cam swaps, I'd guess that its about eight hours of labor, but I'm pretty slow compared to an experienced professional mechanic.
What is the "Norm RPMs" for a 110 Cam at warm idle with a 350 V8 Chevy engine?
The idle rpm is dependent on the LSA and the lobe profile. More aggressive lobe profile cams have less valve overlap than the soft action lobes like most GM cams.
A GM 300hp cam idles at 500 rpm and 20"Hg vacuum.
A GM 350hp (L79/L48/L82) cam idles at ~700 rpm and ~15"Hg vacuum.
A GM 360/370hp (L76/LT1) cam idles at ~850 rpm and ~13"Hg vacuum.
The idle also typically improves with more idle advance, one reason why the later L76 advance specs are recommended (12*-14* idle advance and only 24 degrees centrifugal advance).
While some of the posters in this old thread are no longer with us, their recommendations and comments are worth reviewing (as you decide the rpm and performance bandwidth you want).
I know you've got a smallblock and the pic I'm posting is for a Bigblock, but I'm thinking the X-brace might still be in your way but if it is, drop the exhaust and the passenger side motor mount bolt and it should rotate up enough to clear the X-brace, unless you have factory A/C and then there is no X-brace.
Mike T - Prescott AZ
With a different Cam size do you also need to replace the parts under the engine valve covers too?
The OEM GM cam lobes had very slow open/close ramps that worked well with the comparatively soft OEM valve springs. This combination worked well with the stamped steel OEM rocker arms, pressed-in rocker studs, and OEM pushrods. The entire valve train was engineered as a system.
Most of the aftermarket cams have much faster open/close ramps that require stiffer valve springs. This combination increases the loads on the OEM rocker arms, pressed-in rocker studs, and push rods. So, the suitability of these components will need to be reviewed for any proposed cam swap.
My impression is that if you don't get too wild with the cam selection, the remaining OEM components can still be used (except for the lifters, which should always be replaced).
One way to get a very nice performance street cam that works well with the OEM valve train is to use the OEM L79 cam from the 327-350 hp engine. That cam was designed by GM to work with all the other OEM parts mentioned above. I think that an exact duplicate of this cam (including the slow ramps) is still available from Federal Mogul, Sealed Power, or one of the other manufacturers that make replacement parts sold by auto parts stores. Others here on CF can likely provide more details.
If you do not use an exact duplicate of an OEM cam, the cam manufacturer will likely recommend that you upgrade to stiffer valve springs. If the cam is not too wild, this may be all you need to change.
I know you've got a smallblock and the pic I'm posting is for a Bigblock, but I'm thinking the X-brace might still be in your way but if it is, drop the exhaust and the passenger side motor mount bolt and it should rotate up enough to clear the X-brace, unless you have factory A/C and then there is no X-brace.
Mike T - Prescott AZ
Do you have to "remove" both the radiator and A/C radiator for clearance to remove the camshaft shown above?
Mike - The radiator will definitely have to come out. If the Corvette is a factory A/C car, then there is no X-brace to worry about...just the condenser in front of the radiator. Non-A/C cars will have the X-brace and a good chance that the engine will need to be hoisted up a bit to get the cam to clear the brace.
I believe the factory stopped using the X-brace around '68 or '69. I had thought about just removing it but just couldn't bring myself to grinding off the welds and it wasn't that much work to drop the exhaust and the passenger side motor mount to get the cam to clear the brace. Again, that was for a Bigblock Vette, I expect the brace will be in the way on a smallblock Vette but not positive about that.
Mike T - Prescott AZ
Mike - The radiator will definitely have to come out. If the Corvette is a factory A/C car, then there is no X-brace to worry about...just the condenser in front of the radiator. Non-A/C cars will have the X-brace and a good chance that the engine will need to be hoisted up a bit to get the cam to clear the brace.
I believe the factory stopped using the X-brace around '68 or '69. I had thought about just removing it but just couldn't bring myself to grinding off the welds and it wasn't that much work to drop the exhaust and the passenger side motor mount to get the cam to clear the brace. Again, that was for a Bigblock Vette, I expect the brace will be in the way on a smallblock Vette but not positive about that.
Mike T - Prescott AZ
My corvette does not have the X-Brace.
So, the answer is just the radiator or both the radiator & A/C radiator?
Mike - I think the length dimensions I sent you on a smallblock cam were around 21.5 inches and just measured (roughly) from the face of my 65 Smallblock Coupe to the face of the radiator and it's about 16 inches so my quess is that yes, the A/C condenser will also need to be moved out of the way for camshaft removal along with the radiator.
Mike T - Prescott AZ
Mike - I think the length dimensions I sent you on a smallblock cam were around 21.5 inches and just measured (roughly) from the face of my 65 Smallblock Coupe to the face of the radiator and it's about 16 inches so my quess is that yes, the A/C condenser will also need to be moved out of the way for camshaft removal along with the radiator.
Mike T - Prescott AZ
In my '67 small block with factory A/C, the A/C condenser was not in the way for a cam swap.
04-16-2018, 09:19 PM
