I wonder how many people have their heads ported that shows increase of peak power but sacrificed too much in other RPMs.

Porting the exhaust manifold isn't that hard since it will generally make power. Intake manifold and head, on the other hand, can completely screw up flow velocities and actually lose power.

I'm just started digging into intake manifold porting and found that Mitsubishi did a great job in their design and kept flow lengths very close between all 4 runners. So I'm not sure why runner for cylinder #4 was found to have 9% more flows than cylinders 1 & 2. And how much of this 9% actually makes it into cylinder 4's combustion (I would think the head would reduce this difference)? So tuning to 11.5 AFR, how much richer is 1 & 2? I suspect 4 is leaner than 11.5, but it's exhaust is blended with other cylinders. Could it be 11.8 while other three are 11.4?
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This thread is a great read:
https://www.evolutionm.net/forums/ev...-manifold.html

 

this happens. i tend to see a few trends in head porting discussion. for diy'ers they tend to buy the 'port and polish' kits from summit or jegs that are nothing more than sanding rolls. these pretty much just polish the surface but dont actually move any metal, so very minimal gains are possible. the flip side of that coin is the shops selling porting service tend to focus on flow numbers just like people focus on peak power on dynos. sure you can open up the port a ton so it flows a lot at high lift but even with a high lift cam, you spend a vast majority of your time at low and mid lift, so your hogged out intake ports aren't going to make as much torque and wont et as well.
i was in the ls1 game before all the aftermarket stuff was out, so everyone was porting stock castings and it turned into a flowbench battle for peak numbers.

 

i like this thread quite a bit. i did a second round of porting on my intake recently, but came short of cutting it open like that. I got lazy, and i decided it was diminishing returns because of how thin the casting is, you really cant open it up much. i really would like more plenum volume.
i have my motor out so ill see if i can post some pictures of what i did in the next couple days.

 

I just measured my spare intake manifold and throttle body. Both are very well matched up and even to the head. So there isn't much to do other to modify the plenum. And port out throttle body and plenum opening, but not much metal there to remove before it becomes too thin.

 

The port length is pretty much fixed for whatever model it is.

Lets say you stick to SBCs.
The length is fixed.
Knowing the volume you can convert to average CSA
The CSA should be constant along the whole length...............if it's a good design.

Knowing the CSA , you can go back to a 4G.
Knowing the volume, the length is fixed and you can calculate the CSA.

You can then compare the SBC CSA to the 4G CSA or compare it to any other CSA of any other head.



But NOBODY has yet documented the port volumes of any 4G head.

So why not?

There's more than one 4G head.

There's more than 2.
There's more than 3?

How many different versions are there?


Would you know?

 

I was in the Cleveland game long before anyone knew what a turbo was.

4V Cleveland heads flow far too much and to make more power on a dyno you need to make them flow less on a flowbench by changing the shape because a flowbench tells lies.

That was long before the LS ever hit the drawing board, or more realistically the screen.

 

Gents

Please stay on topic w/out throwing out personal insults.

Its a good discussion / Keep it professional

 

To be honest, I have no clue what they're talking about. It kind of sounds like sports talk.
Looking closer at my spare IM and TB, I don't see much of an opportunity to make more power. TB is flimsy and already thin.I don't feel it's worth sacrificing the structural integrity to make a little more power. The casting doesn't look bad inside the IM, so nothing to be done there either.





I plan to step down the divider walls in hopes that air can travel to cylinders 1 & 2 better. My concern is that cylinders 1 & 2 will make more power at low RPM from longer runners and 3 & 4 makes more at higher RPMs with reduced runner lengths. It's probably already like that now because of the plenum, and I'll probably make it worse. I'll try to take pictures inside each runner to see the differences. From the old thread, I know that cylinders 1 & 2 (especially 1) runners ride higher than 3 & 4.

 

with an attitude like that you definitely cant

i tried to take pictures of my intake runners from the head flange but there was too much glare and you couldnt tell anything that was going on, but i moved quite a bit of material as far as a 6" burr could reach. you dont want to just cut til you see light, you need to move the walls strategically to make the air straight. so on outer runners i moved the outside wall as much as i could and moved the curve back into the runner. also i move as much of the roof as i can(especially in heads) and move the floor as little as possible. this is less important the further you are from the valves, so up near the plenum you can go to town on the floors if you can reach it.

but here is some from the tb side.
i bought a ebay 70mm throttle body for like $90 and it works great.

here it is next to a stock throttle body. notice i moved the gasket from the previous picture to the stocker so you can see the size difference.


here is the tb flange. i had to weld a 1/4" plate to it with a new hole because the 70mm throttle blade is about the same size as the entire original flange.


since the casting is so thin everywhere i had to weld up behind the flange as much as possible so i could open up the tb opening as far into the plenum as the material allowed. i did an ok job but i think the guy in the other thread did better.

 

What happened to the IAC bypass at the bottom of throttle body? Did you remove that completely?

 

I agree to leave the floor alone. We want better flows on top to help fuel keep off the floor.

 

Did you move the runner divider walls as low as other thread?

 

Got a measurement of fellow member's head port dimensions:
Guess I misread the port as head instead of IM, I think this gives me some room to match up on the roof. I'm guessing there's about 2mm of metal that can be removed. This is enough to polish the runners along the red line above.