blue86iroc

iTrader: (2)

I have read all the posts about siamesing the TPI intake runners and/or the base, but I'm still not sure what I should do. I have a 2400 RPM torque converter in my Camaro and a 3" Hooker cat-back system. I know that I need more air coming in to make better use of my exhaust, and I'd like to extend my top end RPM a little more.

I read the large (70+ posts) thread regarding siamesing the base, and a lot of it is over my head. I still can't figure out if it's more advantageous for me to siamese the runners, the base, or both. My intake is still untouched, aside from an airfoil that the previous owner installed. I also plan on burning my own custom chips, so I could calibrate and tune the car further.

I've run a best ET of 14.4 seconds at 95 mph on my L98 IROC-Z. I shifted my auto around 5500 RPM -- I think that I should have shifted at a slightly lower RPM.

mrr23

the weakest link is the runners. start there. i siamesed my base with stock runners and still peak at 4400 rpm. but i have more power in the stock range. but to increase rpm range start there.

blue86iroc

iTrader: (2)

Which end of the runners?

In looking at madmax's dyno sheet, his engine keeps pulling past 4800 RPM. Before siamesing the base, it dropped off around 4700 RPM. He didn't touch the runners. Is that because he took so much (5") of material away? Say, for example, that I wanted to go 5" like he did. What would happen if I "shifted" the location of that cutout and took 2" of the wall away from the lower portion of the runners and removed 3" of the wall inside the base?

mrr23

i did the same thing he did. replace the stock runners with something like slp is what i was getting at. i don't know how he got more rpm out of it.

Fastmax

I would think if you siamesed the base that replacing the runners wouldnt do any good. I mean you have basically doubled the size of the runners by siamesing the base. Each cylinder now has 2 runners that it can pull thru. I wouldnt think that would be the problem why your car wont pull on the top end.

turbotater

i joined my runners so that there is
4 oval shaped runners to feed the base
i now shift at 5900- 6100 rpm
one of my best mods so far
there is a pic already in this section
i'll try and find it

mike

turbotater

http://sethirdgen.org/personal/siameesedrunner.jpg
this should be the link to the pic of my runners

mike

blue86iroc

iTrader: (2)

I really don't want to buy new runners or externally modify the ones that I have... I'd like to keep the engine as stock-appearing as possible. I know that a lot of guys can't pull higher RPMs with stock runners, but I'm willing to take a few old manifolds and see which siamesing depth works best on the base, while still retaining factory runners.

turbotater, how did your siamesed runners affect your low-end performance?

FlamedROC

Just buy Accels Large tube runners. They will improve your RPM range and maintain stock appearance. Only the big time TPI gooro will notice that u put them on

D Stroy H8

I agree - unless you're absolutley obsessive, having ANY large tube runner system looks similar to stock. Even the flashy edelbrock ones with the "speed fins" lol... Since the runners are the choke point hands down, theres no getting around them if you want to see complete eradication of the infamous 5000rpm choking... They have to be heavily modded or just outright replaced! If you're willing to spend a few hundred on stock bases for experimentation, would you be opposed to purchasing AZS&M runners that look almost exactly like stock but flow gobs better?

blue86iroc

iTrader: (2)

If I bought a set of those AS&M runners (or any aftermarket runner, for that matter), I wouldn't have to siamese them at all, right? Therefore, if I bought the runners and siamesed the base, I'd gain more power AND at higher RPMs? Would I even need to siamese anything with aftermarket runners? I'd still like to port match everything.

brian89transam

I think the general concesus is that the only aftermarket runners that could use real porting are SLP's. Runners like Arizona Speed & Marine, Accel, or TPIS do not need any porting and they look stock, although they could be port matched to the plenum and base for a little better flow.

If money is not an issue, you can purchase an Accel, TPIS, or Edelbrock intake base, instead of porting the stock one. These are very expensive, but might be a better choice if you're planning to spend hundreds of dollars on stock bases.

In my opinion, if you're looking for more breathing power and still want to maintain stock appearance and emmissions, and do it all on a budget, you should make a plan sort of like this...

-K&N filters, Throttle body coolant bypass
-Port the plenum
-Either ported SLP runners, or used AS&M or Accel runners
-Ported stock base or used aftermarket base-Edelbrock, Accel, etc.
-Headers and free-flow cat to match your Hooker exhaust.

Remember, all the experienced PROM tuners here say to start burning chips as soon as possible before you make any major changes that make your setup very different from stock. I don't think exhaust and runners would qualify as major changes, but a siamesed intake base might.

Also, from what I've read, manually shifting an automatic with a fairly stock TPI engine does not make your car any faster, since it makes so little power beyond 5,000rpms anyways, and the transmission actually shifts slower when manually shifted.

Well, feel free to critisize. Hope I helped.

blue86iroc

iTrader: (2)

Thanks for your opinion, Brian. I just wanted to respond to a few things that you mentioned.

I've done a few searches on eBay, and stock TPI intake manifolds run anywhere from $30 to $75. Assuming that I could get one cheap, I wanted to siamese the base, in small increments, and do a dragstrip run with each depth. That way, I could see exactly which amount of siamesing helps... 2", 3", 5", etc. The only thing that worrys me with this is the amount of money that I'd be spending on gaskets... they aren't much, but it all adds up.

Assume that I bought Accel runners and an Accel base -- would I have to port match the tubes or would they already be matched up? How much would an aftermarket TPI base cost me?

Based upon the plan that you suggested, I already have my K&N filters, throttle body coolant bypass, and a free-flow cat. I'm looking to add headers sometime soon. I'm also anxious to start PROM burning.

About manually shifting my tranny... I have a Pro-Built TH700 that's designed for street/strip applications. Shifting it manually seems like it works better to utilize the entire powerband throughout all the gears. If I let it shift by itself, I'd be going into second gear a lot sooner (I have to go easy on the gas when I launch or else I won't get any traction... since the pedal isn't initially at WOT, the tranny would shift sooner).

So, to get all of this straight... to maximize my TPI's potential, I can either 1) buy aftermarket runners and siamese the base, or 2) buy aftermarket runners AND an aftermarket base. Is the main reason for siamesing a stock base the fact that it's far cheaper than buying an aftermarket base (and it looks the most stock), or is there some other benefit that I'm not seeing?

D Stroy H8

Well - A fully ported stock base will flow nearly as good as an aftermarket out of the box. However, if you port an aftermarket base, then the stock is lame in comparison even fully ported.

A taste of free flowing TPI:
-Ported plenum
-Aftermarket Runners (not SLP)
-Ported stock base

A bigger taste:
-Portmatch the plenum to aftermarket runners
-Portmatch the runners to out of box aftermarket base

TPI on thoeretical par with full aftermarket intakes like Stealthram, Superram etc:
-Portmatched plenum, to aftermarket runners
-Aftermarket runners portmatched to ported aftermarket base

blue86iroc

iTrader: (2)

D Stroy H8, it looks like I'd be somewhere in the middle if I ported and portmatched a stock plenum to aftermarket runners, which are ported and portmatched to a siamesed stock base.

How much low-end torque would I be giving up if I went with aftermarket runners? The reason that siamesing a stock base seemed so good was because you still retained the low-end torque, since the runners were stock.

Maybe I don't understand what I'd be getting with aftermarket runners. Are they just a bigger diameter, or have they been partially siamesed?

D Stroy H8

You'd keep most of your low end torque.

Two styles of aftermarket runners: Siamesed and Larger Tubes.
Both result in similar gains, however the concensus is that SLP leaves some room for improvement while the others are great out of the box. AS&Ms look very stock, they are just bigger and badder. And yeah I think youd be in the middle with your idea. Keep in mind though, that after putting on aftermarket runners, you can pinch a few pennies back by austioning off your stockers on ebay. Same "rebate" if you plunked down the change for an aftermarket base and auctioned the stocker as well.