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Old 11-08-2012, 11:04 PM
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Shaft rocker questions

I have just pulled my circle track engine as I will not be running for a little while and my S10 needs a new power plant so... I called my engine builder and asked about just swapping out the cam because I thought there would be no way I could run this motor in my street truck, turns out he says all I really need to do is change out my rocker arms for a different ratio.

Currently I run 1.80 and 1.70 on the race car, he says all I will need to do is make it 1.60 and 1.65 and it will be a streetable engine. I have never worked on a shaft rocker set-up as this engine never needed any work and I have no reason to doubt this builder and I dont want to ship it 1200 miles and across the border so are there any issues with just straight changing the rocker arms, anything a guy should know about these set-ups?

I am not a engine builder by any means but i'm sure I can pull off this simple task so long as there aren't any tricks to the shaft rockers


bonuts

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Old 11-08-2012, 11:25 PM
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Quote:
Originally Posted by bonuts View Post
I have just pulled my circle track engine as I will not be running for a little while and my S10 needs a new power plant so... I called my engine builder and asked about just swapping out the cam because I thought there would be no way I could run this motor in my street truck, turns out he says all I really need to do is change out my rocker arms for a different ratio.

Currently I run 1.80 and 1.70 on the race car, he says all I will need to do is make it 1.60 and 1.65 and it will be a streetable engine. I have never worked on a shaft rocker set-up as this engine never needed any work and I have no reason to doubt this builder and I dont want to ship it 1200 miles and across the border so are there any issues with just straight changing the rocker arms, anything a guy should know about these set-ups?

I am not a engine builder by any means but i'm sure I can pull off this simple task so long as there aren't any tricks to the shaft rockers


bonuts
First, what engine?

Going to a smaller ratio decreases the lift and the open duration (a relatively small amount), but whether it will make a race cam streetable depends on quite a few things. Not the least of which is the increase in the dynamic compression ratio (DCR) caused by the changes to the intake closing point. If the DCR is increased too much the engine will be detonation prone and might need race gas.

Another thing to consider is the valve train geometry, which can change when the ratio is changed. Might need different length pushrods to correct the geometry.

In any event, to really know what the deal might be, the compression ratio, all the cam specs, and the rod length needs to be known.
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Old 11-08-2012, 11:52 PM
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Like I said the builder is reputable no reason to doubt them, on my end anyways. What he says is gold to me. I have had a few high HP late model engines built by them and have gone out of my way to get to Minnesota for them to build me reliable HP. It is a 9:1 356, 6.210 rods obviously a roller engine, I can't tell you the cam specs as I don't know for sure. I had the engine built years ago and it has sat for a few now.

Iam going to swap out the rocker arms and see how she runs. More than anything i was worried about vacuum because I do drive my S10 daily. This engine is a 540hp small block so it was relatively low powered compared to most late model guys.

I also have no reason to doubt what your saying as I dont have nearly enough knowledge this far in depth with these engines. I can build a small block but these low compression high hp ones are beyond me.

I have done a bit of research on what this change will do but I've said it a million times I am no engine builder, and I have never played with these shaft rockers.


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Old 11-09-2012, 12:05 AM
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Just reread, guess I never said I trusted the guy! Musta just been thinking it


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Old 11-09-2012, 12:11 AM
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Quote:
Originally Posted by bonuts View Post
Like I said the builder is reputable no reason to doubt them, on my end anyways. What he says is gold to me. I have had a few high HP late model engines built by them and have gone out of my way to get to Minnesota for them to build me reliable HP. It is a 9:1 356, 6.210 rods obviously a roller engine, I can't tell you the cam specs as I don't know for sure. I had the engine built years ago and it has sat for a few now.

Iam going to swap out the rocker arms and see how she runs. More than anything i was worried about vacuum because I do drive my S10 daily. This engine is a 540hp small block so it was relatively low powered compared to most late model guys.

I also have no reason to doubt what your saying as I dont have nearly enough knowledge this far in depth with these engines. I can build a small block but these low compression high hp ones are beyond me.

I have done a bit of research on what this change will do but I've said it a million times I am no engine builder, and I have never played with these shaft rockers.


bonuts
I wonder why 1.5 ratio (stock, in other words) rockers weren't mentioned by him as replacements for whatever is on it now. I can only guess there was some sort of cam lobe lift rule in effect, else such high ratio rockers wouldn't be used.

BTW, you need to find out if the shaft rockers are offset.

The size of the intake runners will have a bearing on how the engine behaves on the street, too. But if the guy who's telling you it will work is the same one who built it and he's reputable, etc., then I'd defer to his judgement.

Last edited by cobalt327; 11-09-2012 at 12:24 AM.
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Old 11-09-2012, 12:19 AM
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Offset? Not sure what you mean, I thought he would tell me to run 1.5 as well as a different cam would be the plan from him. It is currently a T&D shaft rocker setup.

Guess I could have mentioned we were restricted pretty heavily, I ran a 500 2 barrel (a real nice one though) and bowtie phase II heads though they were also pretty heavily worked over.


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Old 11-09-2012, 12:34 AM
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Offset rockers are used on heavily modified and/or aftermarket heads set up to flow a lot. They have the pushrod seat offset from the roller tip. This can give more room for the port w/o the pushrod getting in the way and can allow a larger valve to be used.



Sometimes an offset lifter is used. Offset valve trains use different guide plates than regular, too. Hopefully this is nothing to worry about- there are good flowing heads that use standard type rocker and lifters w/o offsets.
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Old 11-09-2012, 12:43 AM
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Ok, after looking at the engine tonight I would say they are definitely offet rockers. I'm sure the intake rocker was offset from where it should have been, not close to the stock arms. I will have a better look tomorrow but pretty sure I just learned something here.


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Old 11-09-2012, 05:22 AM
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If you could post a picture of the current setup it would be of great help. One question I have is are you planning on staying with the shaft setup or are you going to go back to conventional stud mounted rockers?
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Old 11-09-2012, 07:51 AM
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The oval track 9:1 (or 9.5:1) are built to turn very high RPM. The cams I use are in the 265-270@.050 and turn 8500 to 9000 RPM. All of this due overcome the limitation of the 390cfm carb. Rule changes have meant I havent built one in the last 3-4 years but we were using old NASCAR 18* heads. A set of rockers for those heads would cost about $1200 new, not including the shafts and stands. Maybe I'm way off but I would never try to run one of these on the street, especially in a daily driver. Just dealing with the dry sump would be a pain.
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Old 11-09-2012, 07:51 AM
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what size is the intake valve?
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Old 11-09-2012, 12:07 PM
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It is not one of the old tour style engines that had to run a 390cfm, also not a dry sump, and it was built to run at 7200RPM.

I will get a picture of the setup as it is now. I dont have the build sheet here but I believe valves are 2.05 and 1.6

Need a new engine for my S10 as I grenaded the 377 in the fall and this one is just sitting get more and more outdated, so I'm going to use it, just going to do some minor work to make it as streetable as possible and see how it works.
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Old 11-09-2012, 12:22 PM
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Quote:
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It is not one of the old tour style engines that had to run a 390cfm, also not a dry sump, and it was built to run at 7200RPM.

I will get a picture of the setup as it is now. I dont have the build sheet here but I believe valves are 2.05 and 1.6

Need a new engine for my S10 as I grenaded the 377 in the fall and this one is just sitting get more and more outdated, so I'm going to use it, just going to do some minor work to make it as streetable as possible and see how it works.
I'd just swap the cam- it's likely cheaper than a set of rockers and you can get a more street friendly power band.
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Old 11-09-2012, 02:18 PM
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Got a few pictures and I have no idea how to put them on here, and no idea how to turn them so they are right side up, so they are in my album


bonuts
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