If anyone is still interested in this kind of information. if stock heads are being used.
port entrance. tapered top and sides of runners. stock ports are 1.375" x 1.045". tapering the first inch or so out to 1.56"x1.17".
with entrance porting and port matching at head, the flow is 190cfm vs stock 150cfm

port matching to head. ended up going bigger than photo shows. just a little smaller than head port size.
this relatively easy to do. I would clean up the full length of the runner.

there's more that can be done, but it's a lot more work.

 

I did that to my crossfire back in the day and then later welded in some metal on port entrances to flare them some and ported further.Even the initial porting had a very positive effect.A 1/4" thick lidspacer was also added after 2nd modification.This setup is still on active duty

 

cool. great to hear about crossfire modifications
this is what I ended up doing.
didn't people would want to dd what I did. also ported full length of runner.


also did this to the top. the bumps effect the flow. especially the one with the allen plug in it.

 

That is actually almost identical to mine after round 2 modification except i kept my EGR channel in place and kept the swirl vanes. Very nice work there!. Back when i did round 2 in 1995,i also ported the #624 heads-those eventually developed cracks(was getting oxygen in cooling system,causing chronicly rusty coolant) so a pair of Dart Iron Eagles ended up on engine,raising compression one full point.

 

Thanks, it was a lot of work. I also have dart 165ss/summit racing heads. I did port the dart heads a little. bowl blend, unshroud the valves, gasket match and cleaned up short turn. I've been thinking about modifying swirl vanes to a larger diameter sleeve, because stock swirl vanes restrict flow above a certain cfm. they were restricting my manifold flow.
I destroyed a couple of manifolds before getting to this point.

 

I basicly destroyed my first manifold-breakthrough in several areas coupled with bad welding...it is salvagable though.My Darts are 165 also-right out of the box,valve job was good.Much better heads than the old '624s and fixed the rusty coolant problem. This is on '84 vette L83 shortblock.You may know,but '83-84 manifolds have the little crossover ports between runners and '82 manifolds do not. All the welding on my manifold warped it-got it straight again in a hydralic press

 

Very similar experience. Mine is also 84 vette. warped the second intake and also found the water jackets that are in-between port walls in two places, when porting. ended up buying older intake without the crossover ports, because they flow better on flow bench. last intake was skip welded. checked all gasket surfaces with machinist straight edge. I got lucky. minimum clean up with flat file. probable didn't have to file it. straightening a manifold with a press is a great idea. I imagine that took some patience.
If I do another, not going to weld it solid, not going to use round rod.
all the problems that come with welding is why I originally only posted porting the entrance and port matching. it's a 40cfm gain with minimal work. stock heads with stock cam flow about 185cfm and that simple porting job gets 190cfm intake manifold flow. Anything beyond that is a lot more work.

 

Interesting thread...Did either of you do a before and after dyno test to see how much of an improvement your efforts/cost made? That would be the real test IMO.

 

short answer is no,
I'm in the process of learning how to set up ECM for tuning. not going to be as good as renegade for sure. tried to buy one, but it was too late. It would be nice if they were back in production. I'm not afraid of trying and failing, so here I am. I like learning. All I have is, when the car was in stock form, it didn't do rolling start no brakes burnout. Now it does 20-foot long rolling start no brakes burnout. I know this means nothing, but that's all I got. On the flow bench stock flows 150-155 cfm. modified flows 213-220cfm. I was very conservative with wall thickness when porting, didn't want thin walls. got 225cfm on a junk intake, thin walls. I know this also means nothing.
I'm rooting for the renegade manifold to go back in production. would be perfect for my setup
some day it would be nice to dyno test

 

Big increase in S.O.T.P. performance with the manifold modifications,especially the added metal 2nd round that also included mild port job on the '624 heads-increased RPM capability enough to cause alternator belt problems:flipping over in pulleys or breaking-one incident belt broke at ~5500 and slapped a ~1.5x 5" hole in my SMC hood.A larger,deep groove alternator pulley meant for a '70.5 z-28 LT-1 fixed the belt problem. Still running original '82 ECM with Hypertech '82 vette chip '82 PC board ESC control box replaced with '83 module type because the '82 one was acting up.There is at least one guy on here that has installed a Renegade.

 

Well, good. Glad you are happy and it will perform better than stock for sure. I run a Renegade and mine runs well. Maybe that is two?

 

Yes- KITT1983 would be the other known user

 

at 6 seconds in.
looks like the first 3/4" of the top of runner at entrance has a radius taper. I find it interesting that my welding, grinding and testing lead to similar shape. I was going on the theory that if the entrance had turbulence and flowed like a smaller sized runner. making the entrance bigger would compensate for that.

 

Interesting video. Is that the ~ 1967 z-28 302 "over the counter"GM crossram or something else ? Has that mid-1960s-earlier breather pipe and did not notice a "Winters"casting mark Didn't Smokey Yunik design a crossram manifold?

 

Edelbrock str10 intake. smokey yunik made one and Offenhauser still makes one. there all different. showed edelbrock because of the entrance. can clearly see at 6 second mark on video. that's all.

 

got 230cfm with new port entrance design

hitting the limit for my little flow bench. Just wanted to see what could be done. can get back to this manifold sometime in the future. I have another car project, different brand of car, but what was learned on this project will help the next project.

 

just can't leave it alone.
can't believe this worked!
bumped out radius piece out of 3/16" piece of aluminum. rounded leading edge. was getting 232cfm until raising the top with 2 washers.
raising the top .14", now the runner flows 240cfm. still not max ported runner. starting to believe a max port job can flow 250 cfm with top raised 1/4" and raise the bell mouth another 1/8". I'll show a photo of bell mouth when the actual one is made.

 

What's the best method of blocking the hole where the EGR runner was ??

 

get early crossfire intake manifold 14031372. they don't have the egr holes.

 

lost a few CFM after welding. still rough, need to be cleaned up. need to order some cartridge rolls.
next step is to port #6 runner

 

Curious to see how this turns out, I have a renegade manifold, I removed it and returned to the original after a polishing off the rough castings on the original. I can tell you the longer intake runners and small ports help the engine build torque at low RPM. The renegade didn't get me the performance it promises, after removing and polishing the original the car felt much stronger on the low end, upper end sure, it is choking. The polishing also brought much better idle with it.

 

stock intake flows about 150 to 155cfm no matter what's hooked up to it. stock runners are 1.375 x 1.0625, but can be smaller. port matching helps and tapering the entrance is all that's needed for stock heads and cam. put on header and free flowing exhaust if more power is desired. stock exhaust is restrictive.
this is the manifold I have on car now. 1.4"x 1.1" runners with taper and radius entrance. 215 cfm average bolted up to head. 212cfm head, intake and TB's.
Runners on this manifold is only slightly bigger that stock runners, but more efficient.

this intake is to see how much cfm I can get from stock intake. #8 is pretty much done. #6 is in the process. still not that big of a port 1.56 x 1.1, port matched and tapered entrance. #8 with no spacer flows 236cfm and 238cfm with 1/8" spacer. not worth using a spacer unless #6 needs it. I imagine the middle runners will flow more than the end runners.
this is a lot of work to do, but its less work than the other manifold

 

this is as far as I got today. tested with sloppy clay entrance just to get preliminary flow numbers 234 cfm. should be better after welding. can contour entrance and smooth out transition. this is runners 6 and 8. 1 and 3 should be the same. middle runners should flow more.
I'm projecting middle runners all flowing over 240cfm.
It's very possible this intake will flow 240 cfm average.
sonic test helps a lot.
For me this is plenty of flow for a street car.
I've come to the conclusion that this design works, but current method isn't practical. disappointing! way too much work. too much welding. Needs to be simple with no or minimal welding. back to the drawing board.
To be honest, I don't want to spend weeks porting and welding.

 

Added another vacuum to flow bench. now I can test above 240cfm at same inches of vacuum.
did some testing today.
the one max out runner 1.53 x 1.3 = 250cfm with bell mouth. Not a very efficient runner.
ends runners 1.53 x 1.13 flow 238cfm with bell mouth. I'm sure I can massage runners to get 240cfm
1.53 x 1.13 middle runners will flow more, for sure 240cfm. most likely 242cfm +. middle runners flow about 5 cfm more
this will be at least a 240cfm average.
I think 240cfm is respectable.
wasn't satisfied with this result until now. Just have to do it now.
If someone wants to max out runners and is ok with the possibility of using epoxy. 250cfm is most likely possible. I'm not going there.
going to start making parts next.

this is how I'm cutting or milling, if I had a mill. top of runners. will add pcs. will show progress as I go.

 

I considered adapting or building my own upper when I owned a crossfire car. Flowed nearly 250 cfm untouched and right at 300 cfm ported. Also would have used the largest bore TBI units I could get without the injector pods in the way. With the marine upper and 80mm TB my 383 made 412 whp and 430 wtq through a 4L85E and GM 10.5" 14-bolt.

 

Even the ordinary aluminum L30/L31 truck base has the material to easily hit 300 cfm and will flow 220-230 cfm even with GMs horrible factory port shapes.


Here is the stock port shape.

 

very impressive. that's more than my engine will ever make. thanks for info.
I realize other manifolds can flow more. My goal is to see how much the stock manifold can flow. stock intake flows 153cfm and modified it flows up to 250cfm. walls get pretty thin to get 250cfm. 240cfm is enough for current heads and cam.