a 4" stroke is not too much for long term reliability unless you are going to be running 24 hour endurance races with your car on a regular basis

 

In that case would it not be a good idea to rebuild the engine between races??

 

Unfortunately, there always has to be someone who comes out with a personal remark, and can't leave the discussion as friendly.

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Shirl,

I have redone my graphs, using GM's piston to pin centerline from the LS7 engine, moving the pin up for the difference between a .949 inch pin and a .927 inch pin = 1.1620 inches.
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I also calculated suggested maximum RPM using the following formula:

n = Rod Length / Stroke
Z = Piston Acceleration in feet per second - A safe maximum is ~ 100,000 feet per second squared.

RPM = The Square Root of [2189 x Z / Stroke x (1 + (1 / 2n)]

4.500" stroke - ~ 5,907 rpms
4.250" stroke - ~ 6,160 rpms
4.125" stroke - ~ 6,288 rpms
4.000" stroke - ~ 6,417 rpms
3.880" stroke - ~ 6,547 rpms
3.622" stroke - ~ 6,847 rpms

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Pumba
The thing that concerns me with your free body diagrams is that they address only the rod angularity issue. There is more to building an LS engine that needs to be considered. Take a look at the piston to counter weight clearance at BDC. If the rod is too short the wrist pin boss and piston skirt will contact the reluctor wheel and/or the crankshaft counter weights at BDC. If the rod is too long there will not be enough room for the rings. These physical limitations are the reason that a rod shorter than 6.100" used with a stroke 4'100" or larger will create this interfearance. A determined engine builder can over come these problems with smaller diameter counter weights, external balancing, exotic piston designs, or tall deck blocks, but for most of us this is cost prohibitive and of dubious benefit...
IMHO the physical limitations inherant with the LS design will limit your rod length choices and the minimum angularity that you seem to be advocating. Granted that a shorter stroke will result in less angularity, but it also limits displacement. As I mentioned before, rod angularity has not been demonstrated to be a problem... Given these choices I'll take the additional displacement over improved angularity everytime...
As to your formula for limiting RPM based on stroke, I would like to understand the underlying assumptions in that formula... I routinely rev my 421 LS2 stroker to 7000 rpm and your formula would limit me to 6288 rpm with my 4.125" stroke... I wonder what your formula would predict for a NASCAR engine that revs to 9200 rpm...
Shirl

 

Also having over 30 years experience in race engine building and design and I have to side with Shirl on this.

Not taking anything away from Pumba's statements but the available, conventional documentation and guidelines do not reflect the results of successful, numerous race and street proven combinations that go against the grain.

 

Shirl,

Thanks for the informative note.

Your experience in this matter is very important to any of us who are considering building a high performance LSx engine.

The 100,000 ft per second squared is a generally safe piston acceleration speed. It will be less than this if the engine is using rings 1/16 inch or thinner, due to some ring flutter.

The C6R race engines limit their maximum rpm to 6,200 during longer endurance races.

Concerning another area of the LSx engines, are you using 5/16 inch or 3/8 inch pushrods?

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I'm using hardened 5/16" push rods exclusively. I have bent a few but have not had any valve damage as a result. I prefer to use the pushrod as the prefered failure (fuse) as opposed to bent valves. Also, if you are running higher rocker ratios a larger diameter pushrod will have contact with the cathedral style head on the intake side. L92 or LS7 style heads with offset rocker arms should not have this problem...
Shirl

 

Rebuilt every 1-2 races.

 

Staight from the horses mouth.

 

No one has addressed the question of how Katech gets their 4.18" bore on what I assume is still a C5R block. Any thoughts?

 

Darton sleeves?

 

I think Katech should answer this question.

Also, perhaps they can enlighten us as to why they have gone from the 4.125 inch bore to the 4.180 inch bore?

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Hp (airflow) and endurance/longevity at the extreme - within the parameters set by the sanctioning body.

 

To unshroud the valves for better flow, and to reduce piston speeds. Plenty more reasons but that comes to mind right away.

 

The LS7.R (C6.R) block is completely unique. Beyond that, I cannot go into detail about specifications.

 

Any chance the C6R block will be made available to the public???

 

No

1. It's too unique and would not work
2. Theres too much proprietary info
3. Not many people are willing to pay $20,000 for a block

 

In a backdoor sort of way this answers Pumba's original question.

 

I'm sorta glad that the C6R block won't be sold to mere mortals. After paying $6300 for my C5R, I wouldn't want to be tempted.