I just pulled my upper all apart to install new injectors. I noticed that i have SLP Siamessed runners but my upper still has the divider embetween the ports. Has anyone cut the divider out of the upper to better match the siamessed runners. Im sure it is worth doing but i dont want to take a risk of cracking the upper when i bolt it back down.

 

Done all the time and I plan on doing it to mine.

Check out picture on this site:
http://www.corvetteplenum.com/Basic%...%20Service.htm

 

Well it turns out mine is already done! The guy just didnt trim the gaskets. I realized it earlier when I cleaned all my surfaces.

 

Sweet less work for you!

 

You have a lot of work to do yet...
And yes the plenum is just as big..

 

hmmm, i never knew siamese runners still had a wall/divider inside them.....i dont realy see much improvement over factory if its still divided.

 

Dude, I'd get a sanding roll kit and smooth that out. They polish up easy.

 

They pair them up for the first few inches. It makes them effectively "shorter" and the plenum volume effectively "bigger". It's a bit of a subtle change, but it works. Bumps up the torque curve a little, extends the effective RPM range of the engine a little. Expect no miracles, however.

Way way back in the day when TPI engines were new I bolted on a set of SLP runners (still the same as they are today) and saw NO GAIN. Then I matched the plenum openings to the "figure 8" openings of the runners and they finally delivered on their promise. It was a "desperation move" for me at the time. I didn't want to admit I had just flushed several hundred dollars down the tubes on worthless aftermarket runners. Fortunately, it worked. And it's kinda nice to know it's become common practice to do what I did 25 years ago with those same SLP runners.

 

Def. cut the wall out of the plenum.

Finishing up some SLPs now you really got to go to town to make a gain.
Its not so much a bunch of siamesing but getting 100% enlargement through the entire runner that helps, otherwise your gains if any will be

Dont worry about a "polished" type finish it wont get you any more power.

 

Dude, they are not quite finished in this pic. I have long and flex shaft bits and rolls to get all the way thru.
They don't need to be super jewlery overly polished like i see on this site either.

SLP has 2 major dif designs of the runners.

The very early style has a pair of runners on each side that are open all the way thru.
The newer ones are nothing like the OLD runners. I have a set of each.
I'll take a pic an try to get it put up here of the older ones.

Here is more of them "unpolished"

 

Sorry Bro, Didn't realize that was an in progress pick! I didn't "polish" mine but I did use a cross buff set from Eastwood, I think and it made them look great.

 

damn, now THATS a bit! lol

Perfect for taking those walls down they are a pain even with reg. carbides.

 

This is the first style of runners. The outer casting is diff than the newer runners. The whole casting of the older runners looks like it was done by a freshman shop class.
They need welded all over to have room to port them like the newer runners.
The newer runners have a BB cast in the inner curve older ones don't.

 

Checkout this job....

 

Chevy86 IROC-Z

Looks good. By the way I don't know if you are done with the plenum yet or not but you need to radius the inside of the plenum entrance to the runners. They look to be on the square side in the bottom picture. By the way I used the first style SLP runners on my First intake manifold project.

 

hahaha.... Its not mine. Its this other member who I talk to. Im gonna get mine done by him soon. Here is his name 385IN2005.