Fastmax

I have a 355 TPI that I spent a ridiculous amount of time doing the ports on the corvette heads, matching up the runners, making the base bigger than it was ever intended to be, smoothing the transition into the runners in the plenum etc etc. I also worked over the edelbrock TES and replaced the flattened stupid pipe to open everything up. The car already pulls longer and stronger than I ever expected it to. Its a tractor down low (which I expected) and then pulls hard right into and well over the 5K mark (which I didnt expect). About the only thing I did not do was siamese the plenum to match the siamesed SLP runners. It would be great to increase the upper RPM pull even further. Is it going to be worth my time to rip the plenum back off or are the siamesed SLP runners already effectively shortening up the runners and its a waste of time? Perhaps even port into the divider on the SLPs a bit more? Heres the rest of my setup.
89 IROC-Z TPI
All the free and cheap mods you can think of
355 Cubic inch 9.5 to 1 compression
Fully ported corvette aluminum heads w roller rockers
214/224 duration camshaft
Fully ported stock base and plenum
SLP runners
Edelbrock headers
Hooker Catback
700 R4 with shift kit
2200 RPM stall converter
3:42 Posi Rear
Thanks for the help.

OMINOUS_87

When in doubt, hog it out.,

1989GTATransAm

iTrader: (3)

The answer is yes. Mine pulls hard to 6000 rpm and it still has plenty of torque down low. I just installed the B&M governor kit to adjust the shift of my 700R4 to the upper 5000 range. After the dyno tune I will fine tune the shift point to match my horsepower curve. It was shifting around 5200 rpm mark witch was to low for my combo for good track times.

I have Trick Flow heads, ZZ9 cam, fully ported plenum, Extrude Honed Edelbrock TPI intake and SLP runners with one side fully siamesed and the other siamesed at the top and bottom. I also have a very good cold air intake system with a 3 1/2 inch pipe except for the MAF and an excellent exhaust system. Allen

TexasB4C

iTrader: (1)

Do SLP runners come stock on a 92 B4C?
I plan to port and polish the heads, install 1.95 intake valves to replace the 1.85 305 head ones, siamese the runners and plenum and port match everything.
Do you need to replace the PROM after doing all this? Ive been told yes and no?
Any help would be great
thanks

1989GTATransAm

iTrader: (3)

The SLP runners are an aftermarket product. However GM at one point did sell them through the dealerships. Allen

vortec77

Hey, I have the SLP siamesed runners on the car now, and before i put the plenum on I was thinking of siamesing it. I didnt do anything to the SLP runners and i dont think im going to either, but i to am curious to know the feedback on this as well. Also if i did do this, does anyone know if any body sells plenum gaskets for the siamesed plenum or do i just cut the gaskets to match the material of the plenum?

TexasB4C

iTrader: (1)

on the thirdgen.org technical articles site they have instructions on siamesing the intake and runners and they said to get a TPIS big mouth gasket and use that to find the size to port it too, and just cut out the center of it to siamese them
what does anyone know about an MSD setup for a 350 TPI what type of box and coil and all that would i need, i plan to do extensive mods and have been told when you start to get more air in the Comb. chamber you need to get more spark and more fuel via an Adj fuel pressure reg. which i have installed now, so i next plan to get an MSD system, what do you guys think?

90formy305

Definately siamese them. If anything it couldn't hurt, right? I've done my plenum and into the runners some. I've got a 305. With a 355 I'd do it for sure. The more air the better. And with the camshaft you have I'm sure you'd benefit even more from it. And let's face it, it only takes like 2-3 hours to do this with a die grinder(that's removal, porting , and installation).

Texas:
I run an MSD 6al w/there GM Blaster coil. Easy install and much better gas mileage. Improved throttle response too.

1989GTATransAm

iTrader: (3)

If you have siamesed runners from SLP you do not need that post in the way on the plenum. It will just cause turbulance which means less air flow. The objective is to cut down on turbulance so port match the plenum to your runners and remove the post. Allen

vortec77

anybody got a picture of the post your talking about? and also the egr walls at the front of the plenum?

1989GTATransAm

iTrader: (3)

I called it a post but in reality its the metal between the two circular ports. Looks like a post in the way when the runners are hooked. Sorry about the confusion. Allen

J.E.B.

[quote=1989GTATransAm;2112115]... SLP runners with one side fully siamesed and the other siamesed at the top and bottom.

I realize this thread is kind of old, but could you explain the theory behind this? Which side did you do what to and do you still think it is beneficial?
I'm assuming the concept is one side flows better than the other and needs more "help". What about front to back? Would enlarging the runners (or the entrance to the runner) on certain cylinders more help equalize flow, or is this nit-picking?