Ok I have a set of SLP runners that I have been doing my own version of 'mega-porting' like seen here; http://www.corvetteplenum.com/Mega-p...%20runners.htm

However I have been considering siamesing the runners and intake like seen here; https://www.thirdgen.org/siameseport

What I would like to know is your opinions of siamesing or not, pros and cons. What gains are to be had by siamesing, what gains are to be had by staying ported.

Pros/Cons.. what are you experiences?!

 

By siamesing the intake manifold you are effectively shortening the runner length. Looks like he went a couple on inches into the manifold. The Edelbrock manifold has something like a 6 3/8" runner. Now you are down to a 4 3/8" runner. Combine that with say a 5 1/2" runner in the head you have a combined effective runner length of 10 inches. IMHO that is to short. You need something in the 13 to 17 inch range.

What you were doing with the SLP's was just fine. Siamesing the top portion of the runners so that the top of the divider is flat with the bottom of the top opening. With my new setup I will be doing with the First intake I'm shooting for a runner length of 13 inches. I will be adding some back into my SLP runners. Part of the Helmholtz wave length theory.

 

Interesting.. so I should stop where I am then. BTW I'm using the TPIS Bigmouth intake which I believe is esentially the same as the Edelbrock one.

 

Right, Edelbrock makes the Bigmouth intake. From what I could see of your combination what you were doing was just fine.

If you really want to get serious buy some telescoping gauges and a dial caliper and open up your intake manifold and runners. Get as big a cross sectional area in the runners as you can and still maintain a good gasket surface area. I had my SLP's welded up so I could go to a 1.7" diameter where the runer meets the intake manifold. You cannot go that big with the standard SLP's.

You will need to check your intake manifold runners for cross sectional area. The smallest point will be about an inch from where the manifold bolts to the head. Open this area as much as you can without breaking through.

 

By reading this post did I over do it on my porting?
Heres my engine specs:
Engine:
383 L98 TPI, 350 bored .030 over truck block 4 bolt main honed and magnafluxed
Engine Modifications:
Stock plenum ported for the runners and throttle body
Edelbrock intake manifold and runners
Edelbrock Performer heads 64cc & 160/202 intake/exhaust
Edelbrock Valve Covers
Edelbrock 58mm Throttle Body
Ford 24lbs. Injectors w/ high performance fuel pump & Holley adj. fuel pressure reg.
Manly Pushrods
Crane 1.6 Roller Rockers
Comp cam Hydraulic roller:
510/540 gross lift
Duration at .050 intake:230/exhaust244
Lobe separation:112
Keith Black hypereutectic 10:5: 1 pistons, Molly rings
Scat forged piston rods
refurbished truck 400 crank turned down
Moroso 6qt. Pan
Edelbrock water pump
MSD Blaster coil
MSD box 6AL
Accel 8.8 wires with heat retarded sleeves
Edelbrock 1 5/8 Ceramic Coated Headers
3” Flowmaster Cat-back
SLP cold air induction
Grantanelli adj. mas senser
Transmission:
Transmission tunnel mounted torque arm w/ DS loop
Re-Built 700R-4 Trans w/ B&M 2500 stall
My porting pics:





What I could not get with a Bridgeport I finished up with a Sawzaw and a die grinder with a extention.




I was able to get down to 4-5 inchs in each of the runners as well as simeising the plenum. And I'm planning to do the same to the manifold.
So being that I have a 383 engine with a big cam and Performer heads will I be ok or what?
(the last couple of pics are before I finished the roughing of the runners.)

 

You are OK. You need to round the square dividers. On a 383 with that cam you could do a lot more. Like I posted above you also need to open up the intake manifold runners.

 

Hell i think you could do more... Could use more stall too.

 

https://www.thirdgen.org/siameseport

Where are you guys finding these articles???. I dont see it listed under tech articles or anywhere else on the site.

 

my understanding was that edelbrock made both but TPIS ports there runner openings already...and thats why its like 100 bucks more expensive. pics i have seen of the edelbrock base show small runner tube holes with LOTS of room to port.

my accel superram base had tons of room to port and i really opened them up before i sold it.

now i'm goin for LT1 intake conversion i think. 3 inch runner.

if i had TPI i would siamese it down to 10 inch runner or so to get nicer powerband than the short runner LT1.

 

Thanks for the replys guys! I'm still in the process of porting all the intake system. Also What would be a good stall to go with as was metioned?

 

Probably 2600-3000rpm stall.

 

I was wondering how much of a difference it would make to do that to the stock runners and plenum if your short on cash but have a warmed over motor???????

 

So just a few hundred more rpms in a stall makes that much difference?

 

with a siamesed TPI i would like a 2800-3000rpm stall. for regular TPI 2500-2800. i have a 2800 and i think its just about perfect. siamesing will flatten out the torque curve and reduce peak tq.. and may actually move peak torque to a slightly higher rpm. so i think a 2800 to 3000 would be optimal for that, if you have a fairly mild TPI cam/heads setup.

more radical siamesing and more hot motors might want more stall...depending on the motors torque curve. TPI motors generally make tons of lowend, so they dont need big stalls.

 

I thought siamesing the base intake's runner entry points was supposed to make the incoming air turbulent or something?

 

Not if done correctly. However it really shortends the effective length of the runners. MadMax has experimented in this area and has poster results. Would have to do a search.

 

1989GTATransAm thanks for all your input. What, in your opinion, is the ultimate runner length?

Ok so I made some time today and got back to the bench and pretty much finished off porting my runners. Check image. The finish is a little rougher then I'd like (although it is smoother then the original cast) perhaps I'll be able to find something to 'polish' it out.

Next is work on the plenum. Porting out the where the runners install is a no brainer.. just ensure they're exactly the same size as the runner openings, or a little smaller. This is so there is no 'ridge' for the air to catch.

How about the intake side of the plenum? I'm going to be running a 58mm throttle body. I can see there is alot of 'meat' that can be cleaned out and ported off. The plenum I got with my runners is already ported out a bit, but I can see where there is alot more that can be done. Again, check image.

Now what about the intake? I've got a TPIS Big Mouth intake and although I havn't verified the size of the runner intake ports, they appear to be larger then an Edelbrock intake. Is there any work I can do here to port out the exit side of the runners or on the intake?

I don't want to siamese the intake for fear of shortening the runner length too much. I'm considering on sending off my plenum to corvetteplenum.com because his look like a work of art.. then again he is using a CNC machine. I'll fart around with mine some more and see what kind of results I can get.

 

The answers you're looking for is based on what you want and can be calculated accordingly. (i.e. where you want peak torque to happen and you also want to consider what your rear end ratio is, as well).
See here: http://www.team-integra.net/sections...?ArticleID=471
and here: http://enaf1.tripod.com/teche.html#helm

Just some other information found here:
http://stealthram.com/flowcomparison.html
with dyno curves found here:
https://www.thirdgen.org/forums/tpi/...feb-super.html
to give you an idea of what you could expect for a given runner length.

Hope this helps (if not, confuse you).

 

Those are good. Here is another site. Look at intake runner calculations and a couple of others on the intake.
http://www.wallaceracing.com/Calculators.htm

 

Check image below for what you can do to your plenum with sandpaper rolls and some time. When I bought mine, it was supposed to be already "done" by corvetteplenum.com but was in need of a good bit of cleanup, which leads me to believe it was either done before he used CNC equipment, or I was lied to. I had originally intended to let him do my new SLP runners and match my plenum to them, but after waiting two weeks for a reply to a simple inquiry, I decided to do everything myself instead. Irregardless, I finished up what was started.

You really need to get accurate measurements of all ports, so you aren't just grinding away blindly.