for people that have ported out the slp runners i would like to know how far back did you move the divider on the plenum side?

or should this be done at all?

could i also get a set of big mouth gaskets and port the runners and base to match at the same time?

 

Thats basically the plan. Cut that divider back as far as you can reach or feel like going. And port matching the base, runners and plenum to big mouth gaskets is a good idea too. Or again at least as close as is reasonable. And remember you want the opening in the base to be at least as big as the runners if not a little bigger, not a step the other way.

 

I have unported SLP ss Runners, unported SDPC Vortec TPI base, I have cut the dividers and port matched the upper to the runners on top and ported the TB openings to match my holley 58mm tb. My questions are: are the big mouth gaskets bigger than my ports on the vortec base? What else should I do to this setup? I dont want to siamese the base, but if the big mouth gaskets are bigger than the base's ports, should I port the base and the runners (bottom side) even though I didnt enlarge the top side of the runners? If above is recommended, what kind of gains or losses or changes where peak power is made should I expect? Any info would be cool!

Thanks,
Mike (1bad91Z)

 

Ok its simple if you buy a set of big mouth gaskets and find there is a difference in size then yes by all means port the manifold and the runners to match its that simple. Unported slp's is no where near as good as at least a little work to the opening on the plenum side.

I would get the gaskets and get to work with a grinder to make everything equal and flow properly.

 

I left my SLP runners un ported for the time being, in other words I left them the stock Siamesed size and length that they came, I figured since you guys say I'll lose a butt load of bottom end and its to much flow unless I have headers and a cam. SO I left them be until I get both.

Am I getting any kind of gain out of them the stock siamesed size they are now? They came about 2 inches deep and 1/2 an inch wide. I have a fully ported plenum.

 

I actually removed an inch at a time from the divider on my old combination. That was fun. What I found was you come to a point where the et levels off while the mph continues to increase,,, then the et starts to fall off when you remove too much. That point (or over all length) will be different for different applications. However, based on my experiences siamesing the base is not the fix all to TPI and could damage your engine even if you think you know what you're doing.

 

Well one thing you don't do for sure is Siamese the base in a 305, you will lose as my friend calls it " the life blood," or tork, the power behind 305 TPI's. Porting the manifold is ok, getting an after market manifold is ok, but Siameseing the manifold is one big no no.

A 350 on the other hand is a different story.

 

BadSS
what was the right depth that you cut the divider back for your application. and what is your set?

 

i have a siamesed base on my 305 and in similar weather i only lost 1 tenth and 1/2 a mph, but that was running on aired down drag radials which could easily account for it at least being a wash.

But a cam is in the works, etc....

 

Out of curosity which cam are you going to use Ed I know its a well thought out choice so I for 1 would like to know thanks.

 

The wife’s IROC is a flat top 355 with box stock G1 Twisted Wedge heads (casting flashes removed only and Comp springs), 218/228 –110 cam, 1.625 Headman shorty headers, 3” Race Series Dynomax exhaust, homemade ram air, and gutted MAF. The TPI system I was using was a fully ported (not siamesed) GM base, gutted TPI plenum, and SLP runners. The drive train is TH350, 2500 stall and 3.23 gears, totally stock suspension with 26” ET Streets. I ended up “D” shaping the runners and removing the divider as far back as I could, but the ET increase had leveled off and the last inch removed had no effect on MPH.

I would suggest what I did only on a near identical application. Variables effecting you optimal length would be cid, head flow, compression, cam lobe spread (and centerline), gear ratio, weight of vehicle, stall speed, and traction,,, to name a few - - not to mention the diameter (and shape) of the runner itself. All are important when determining optimal length for your application. The few TPI inductions that I’ve actually ported on (modified and ported on many carbed intakes though) seem to favor a balance of velocity and flow. Meaning in my limited experience with similar TPI combinations to mine,,, it seems keeping the velocity as high as you can while still proving enough flow not to seriously compromise you cylinder heads seems to work pretty good for the long runner TPIs.

However, if you’re having trouble hooking you can go larger with the diameter and shorter with the length. You also might like the balance provided – which can be a compromise between the best quarter mile times compared to how the car pulls from a kick (increased RPM). So,,,, determining optimal runner diameter and length is a per application thing. That’s why I kept pulling the things off and modifying them until I found what worked best for our IROC - even though I had a pretty good idea of a starting point! I will say this that it appears going larger with the diameter seems to help flow while not effecting the torque band as much as length. I think that’s probably why the AS&M runners seem to work so well on a large number of applications.