4 Bearing cam in 3 bearing head

[gtblast]

Can I use a 4 bearing cam with .430 lift in a 3 bearing head without any issues? I know I can run a stock 4 bearing cam in a 3 bearing head with no problems, but I want to know if the increased lift of the hotter 4 bearing cam will cause any problems?

[First opel 1981]

Originally Posted by gtblast Can I use a 4 bearing cam with .430 lift in a 3 bearing head without any issues? I know I can run a stock 4 bearing cam in a 3 bearing head with no problems, but I want to know if the increased lift of the hotter 4 bearing cam will cause any problems?

You have to block off the extra oil port in the head if you are putting a 3 bearing cam in a 4 bearing head.

[gtblast]

Originally Posted by First opel 1981 You have to block off the extra oil port in the head if you are putting a 3 bearing cam in a 4 bearing head.

This I know, but I don't think you read my post correctly. I am asking about a 4 bearing cam with higher lift in a 3 bearing head.

[First opel 1981]

Originally Posted by gtblast This I know, but I don't think you read my post correctly. I am asking about a 4 bearing cam with higher lift in a 3 beraring head.

I read it correctly. I wasn't going to comment on the part I am not sure of.

[CDN OpelNut]

I am running a 4-bearing Isky OR-66 cam (.430 lift) in a 3-bearing head right now. I have no issues but I have dished pistons. You may run into problems with flat-top pistons.

[gtblast]

Originally Posted by CDN OpelNut I am running a 4-bearing Isky OR-66 cam (.430 lift) in a 3-bearing head right now. I have no issues but I have dished pistons. You may run into problems with flat-top pistons.

Yes, I am thinking of putting this cam in my 1970 with the original flat top pistons. I spent some time searching and from what I have seen, it looks like it should be fine for piston clearance. I did not know if the cam might suffer from some sort of flex with only the 3 bearing support and incresed lift. Sounds like you are running it with no problems.

[gtblast]

Originally Posted by CDN OpelNut I am running a 4-bearing Isky OR-66 cam (.430 lift) in a 3-bearing head right now. I have no issues but I have dished pistons. You may run into problems with flat-top pistons.

Did you order your Isky cam from Isky or is that what OGTS sells?

[CDN OpelNut]

Same cam but I ordered it direct from ISKY online. It was far cheaper.

I only have a few hundred miles on my set-up but I don't think there should be any flex issues.

[First opel 1981]

Originally Posted by CDN OpelNut Same cam but I ordered it direct from ISKY online. It was far cheaper. I only have a few hundred miles on my set-up but I don't think there should be any flex issues.

Just curious, where are you getting your lifters?

[CDN OpelNut]

I had the benefit of time with my build. I bought my lifters from a source on E-Bay UK - also at a greatly reduced price.

[opelnut10]

Originally Posted by First opel 1981 You have to block off the extra oil port in the head if you are putting a 3 bearing cam in a 4 bearing head.

You will not have any issues running that cam in that head even with flat top pistons there are no clearance problems. You will need to put a .030 shim under the valve springs to get the proper spring pressures for that cam. If you are running the rotator under on the exhaust valves, the shim goes under the rotator not the spring. Hope that answers your question

[First opel 1981]

Originally Posted by CDN OpelNut I had the benefit of time with my build. I bought my lifters from a source on E-Bay UK - also at a greatly reduced price.

I do have the benefit of time. The rebuild I will be doing isn't associated with a body (yet).

[wrench459]

I would love to know if your getting a true lift of .430 at the valve with the stock rocker arms?

[gtblast]

Originally Posted by wrench459 I would love to know if your getting a true lift of .430 at the valve with the stock rocker arms?

I am not sure which one of us in this thread you are asking, but I don't have a clue. I am just building up an engine for my 70 and wanted to bump up the cam a little to help it out some.

[opelnut10]

Originally Posted by wrench459 I would love to know if your getting a true lift of .430 at the valve with the stock rocker arms?

In answer to your question, No, not with stock rocker arms. Cam Manufactures advertise cam lift based on lift with a 1.5 rocker ratio and stock Opel CIH rockers are a 1:44 ratio. If you really want true lift you have to measure lobe lift, at the lifter with a dial indicator and multiply by 1:44 and that will put you in the ballpark, if the rockers you are using are all truly 1:44 and not all of them are.

[kwilford]

Originally Posted by opelnut10 In answer to your question, No, not with stock rocker arms. Cam Manufactures advertise cam lift based on lift with a 1.5 rocker ratio and stock Opel CIH rockers are a 1:44 ratio. If you really want true lift you have to measure lobe lift, at the lifter with a dial indicator and multiply by 1:44 and that will put you in the ballpark, if the rockers you are using are all truly 1:44 and not all of them are.

As I understand it (and I stand to be corrected), the stock Opel rockers with the sliding tip design actually creates a "variable" rocker ratio, from as low as 1.4:1 to as high as 1.51:1 (or thereabouts) and this ratio also changes throughout the lift height. Furthermore, the ratio is more a function of the as-installed rocker geometry, as it relates to the base circle of the cam, cam lobe height, and valve stem height, rather than particular rockers.

FWIW

[opelnut10]

Originally Posted by kwilford As I understand it (and I stand to be corrected), the stock Opel rockers with the sliding tip design actually creates a "variable" rocker ratio, from as low as 1.4:1 to as high as 1.51:1 (or thereabouts) and this ratio also changes throughout the lift height. Furthermore, the ratio is more a function of the as-installed rocker geometry, as it relates to the base circle of the cam, cam lobe height, and valve stem height, rather than particular rockers. FWIW

The Industry Standard used by cam manufacturers for advertised lift is with a 1.5 rocker. Any time you are using a stamped steel rocker the ratios can be all over the place because of the stamping equipment used to make them. I have seen very smart engine builders that built Stock & Super Stock motors sit down with boxes and boxes of rocker arms to get 16 matching ones where stock rockers are required for the Class. It is true that base circle, cam lobe placement and cam timing plays a large part in the total performance of the cam being used and the most accurate method is to measure the cam lift a .050.