Intake Port Tumble

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redlined

redlined

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These are '90 360 pickup 308 intake ports, and as you can see the mismatch is awful, about 3/16". This gasket is very close to the Air Gap's port size. If I open the port to gskt size, looks to me like that will only induce more tumble on the backside of the pinch.

I'm going to pare down the pinch as much as I feel comfortable with, to around .050" thick wall in the pushrod hole, but even then it would still be a huge ski ramp for airflow if gskt matched.

Any options here, such as splitting the difference with some epoxy in the manifold? Do I need to just get the smaller ported Performer to use with these heads? Already have the Air Gap, but if it's useless with these ports so be it.

I had the bowls cut, and I've blended them to a nice shape, but the factory intake port windows suck. Any fixes?
 

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I opened MY 308s to the 360 gaskets,....we'll see how it goes
Refurbished308heads003.jpg
 
That wall where the intake port on the head intrudes into the intake runner (being smaller) does more damage than the slight tumble you may see. If you open them up to gasket size, I think you'll be pleasantly surprised. Do you have any pictures of your bowl work?
 
The best choice for intake using the Stock heads would be the Weiand Stealth. Its a better match and they fit better to the stock heads than the RPM.
 
What sucks about this whole deal is that these heads started out as a run of the mill valve job, nothing fancy. I told the guys to do whatever they needed to put the heads in good shape. They did the guides and seats, but left a ridge in the pockets when they cut the old seats out. Looked like hell, so I requested a pocket cut. Partially my mistake, I should have just hand blended and went on with my rat mashin'.

For whatever reason,{I suspect general stupidity} they cut the 60 deg angle off the seats, leaving only the 45, and the top 30. I specifically requested a cut to the ID of the seats. Their cutting out the bottom 60 removed a huge amount of metal, requiring copious amounts of grinding to blend in. I was pissed, but decided to blend the pockets and go with it. My 1.88's now look nearly like 2.02 pockets, and the two angle valve job....well.

I'm putting them on a 360 slated for my 4x4, with a .470ish roller designed for computer compatiblity and torque. I had other plans for this motor originally, which included aftermarket heads, but my 4x4's motor has developed a rattley wrist pin after 10 years. Anyway, this tail chasing has the run of the mill valve job turning into ported heads.

Since I'm having to do a bunch of cleanup on the pockets to cope with the machine shop's screw up, I've decided to enhance the VE as much as possible given my meager skills. I didn't need the huge pocket cuts, nor do I need a large port volume since my goal is moderate RPM torque. This motor might see 5000 rpm on occasion, but not often. My goal with the port windows is simply high velocity and smooth flow, and a mild cleanup of the walls with minimal removal. I'm afraid the pockets are to large now anyway, and I don't want to do any more harm.

I don't have any pics of the finished pockets, but you can see the mount of metal removed from the cut on the chamber marked #8.
 

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On the port work - My approach has always been you can help the air go around the pushrod turn area two ways. The goal is to add a small amount of volume: You can push back the PR-side wall and thin the shared wall side (widening the pinch). Or, you can smooth the casting flash and blend the curves from the port entry (gasket size) to past the PR side and spemd more tim on the shared wall side and roof. I raise the roof slightly (leavin the gasket size at the flange), push back the shared wall slightly, and reduce the radius on the shared wall-to-roof intersection. The intake charge predominantly uses the roof and "inside wall" (the pushrod side) so by smoothing these but not creating a small radius "corner" on the roof-to-PR wall intersection you dont add dead spots to the flow. That's an approach that works for me on a street or high torque head where the cam will be medium to moderate size anyway.

On the intakes - In my experience the Wiend intakes are no better than the RPMs in terms of port match up... They all have accurate ones and "off" ones they ship. The last one I had was horrid before I fixed it...lol.
 
It seems I have few choices. Find an intake with a smaller cross section, or put a steep angle on the entry at the pinch and do what I can to decrease the radius over the hump.

I suspect I'm fighting a losing battle anyway, as you can see in the pic of the intake pocket, the removal of the 60 deg angle has left a rather large reverse radius under the seats on the short side. This was done by a shop that's been in business since 1958, you'd think they'd know better.

I'm not sure how much meat is in the short sides on these heads, but given the overall lousyness of these castings I'm afraid to go any farther towards the seats, so I'll have a dead area there as well. Anyway, here's a couple pics of the unfinished pockets. Still have some work to do so be kind, I'm no professional lol.
 

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A word on the bowls... Again, volume is more important to me than shape. You do not want the bowl volume too large if you're not porting the rest of the port a bit too. The shape you have is fine and in fact a nice taper to the seat angle is a good thing, epecially for low and mid-lift flow.
BTW - years in business mean nothing. In fact, a lot of really old shops plain suck.
 
moper said:
On the port work - My approach has always been you can help the air go around the pushrod turn area two ways. The goal is to add a small amount of volume: You can push back the PR-side wall and thin the shared wall side (widening the pinch). Or, you can smooth the casting flash and blend the curves from the port entry (gasket size) to past the PR side and spemd more tim on the shared wall side and roof. I raise the roof slightly (leavin the gasket size at the flange), push back the shared wall slightly, and reduce the radius on the shared wall-to-roof intersection. The intake charge predominantly uses the roof and "inside wall" (the pushrod side) so by smoothing these but not creating a small radius "corner" on the roof-to-PR wall intersection you dont add dead spots to the flow. That's an approach that works for me on a street or high torque head where the cam will be medium to moderate size anyway.

On the intakes - In my experience the Wiend intakes are no better than the RPMs in terms of port match up... They all have accurate ones and "off" ones they ship. The last one I had was horrid before I fixed it...lol.
Click to expand...

These heads have a touch under 3/16" discrepency on the PR side, think it's feasible to mate them with the RPM? I already have the intake, still new in the box. I guess my question is, would the difference in port widow turbulence be worth another $250 or so for an intake with a smaller cross section and higher velocity?
 
Well, this is about as good as it's going to get working with the meat that's available on the intakes. I cut into the VC bolt holes slightly removing the lumps, and the pushrod pinch is getting pretty thin as well. I made a template for width, then laid the angle of the pinch back as far as I could.
The cross section is still only .750", but I had to work off of the thinnest pushrod hole and make the rest of the ports' cross sections match. I put as gentle a radius as possible on the turn into the port behind the hump.

Opinions? Also, what should I do with the oddball guides? Anything other than maybe teardrop the bowl?

The center exhaust ports I just straightened at the exit, came out a pretty decent shape, about the same size as the 1-7 / 2-8 ports, which I just lightly cleaned up.

{I'm buying decent heads next time, the hell with all this grinding lol}
 

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Mine are at the shop right now, this is what they look like. I took the edges off the guides and cleaned them up some. The rest will be done by the machinist. The exhaust look great it's the intakes that need some thought. I'll post some pics when I get them back. What rpm do you want out of yours?? You might think about getting chevy valves for the smaller stems, that was mentioned to me. This motor is going in my convertible, so it's a cruiser/bruiser.
 

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MRL Performance said:
The best choice for intake using the Stock heads would be the Weiand Stealth. Its a better match and they fit better to the stock heads than the RPM.
Click to expand...

That is something I used to write and tell people all the time Mike.
Even Locomotion has found it best on his car. (though he always writes "for my application " LOL!

IMO, people always want proof positive facts and. Numbers over the best advice even if it was from the been there and done that guys
 
rumblefish360 said:
That is something I used to write and tell people all the time Mike.
Even Locomotion has found it best on his car. (though he always writes "for my application " LOL!

IMO, people always want proof positive facts and. Numbers over the best advice even if it was from the been there and done that guys
Click to expand...

Well, how about you write and tell me what to do with the oddball 308 intake port roofs Senor Donethat?:prayer::D Should I modify them or leave them alone? Just teardrop the guides in the bowls and let it go?
 
redlined said:
Well, how about you write and tell me what to do with the oddball 308 intake port roofs Senor Donethat?:prayer::D Should I modify them or leave them alone? Just teardrop the guides in the bowls and let it go?
Click to expand...


The Stealth "might" be a better intake on certain builds (although unless memory serves wrong all the tests on both strokers and 360s I've read about that included both the RPM beat it) But fit-wise it is no better than anybody elses.

On the roof - The 308s are designed to induce swirl. Hence the tapering and twisting of the guide boss. If it were me, I'd pretty much leave them alone. The "less is more" theory. IMO the entry work you did was good.
 
OOTB, the RPM has larger port openings than the Stealth. So OOTB the RPM flows more air. On my bench, the RPM's average flow is 243cfm, the Stealth is 224cfm. But the Stealth has larger runners than the RPM. Once you open the port openings to the same size as the RPM, the average flow from the Stealth shoots up to 275cfm.

And the Stealth fits better with stock heads than the RPM. If you put a Stealth intake on an engine with RPM HEADS, there is a gap between intake and head because the intake is a bit narrower than the RPM. With stock heads, the RPM intake generally rides high, the Stealth rides lower and fits better.

With RPM Intake and RPM heads, everything fits good. Stealth on an RPM Head, not so much.

Just my 2 cents, been there, done that with these intakes
 
"OOTB, the RPM has larger port openings than the Stealth"

What I've been saying is out of the box they both suck due to shift. Attached is a pic of the Stealth I fixed, before and after.
 

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redlined said:
Well, how about you write and tell me what to do with the oddball 308 intake port roofs Senor Donethat?:prayer::D
Click to expand...
I read it as a snotty reply. True or false?

WOW Moper, worst one I seen yet. I also bet they get worse though.

MRL, ever flow test a ported a RPM? I have seen Hughes for example offering a service to do such work. I do not remember them publishing a result.
What would you charge if you do port intakes?
 
rumblefish360 said:
I read it as a snotty reply. True or false?
Click to expand...

False. No snot intended. It's just that I have asked two or three times so far about the oddball guides and at the time no one had replied. {Thanks Moper} You stated people don't take advice from people who've done it. I realize you were referring to manifolds, and my first question was about that, but things have advanced beyond the intake, as you'd have ascertained if you'd read the post. I don't have a flow bench, hence me being on here asking questions of those that have indeed been there done that. I don't have a bench or spare heads to research what works and what kills them, so random grinding in hopes of a good result is out.

I asked whether or not the difference in manifolding alignment was worth another $250, and that went unanswered by anyone, so I decided to just stick with the RPM, since I had it laying around. The port windows and pockets are done for better or worse, on to the guides.

As yet, I still only have one opinion on the guides, and I'm inclined to agree with Moper, leave them alone for the most part.

What I'd REALLY like to know at this point involves the shape of the guide in the bowl. If the flow does indeed have spin around the axis of the valve, induced from the curved guide, should the teardrop shape be angled more in the direction of the swirl? Or equal on both sides like a regular port, or just left flat on top as cast?

The guide's shape in the bowl looks more like a rudder to me, with the narrow straight areas and deep hollows on each side. The flat area on top looks designed to induce tumble. Odd combination of shapes even for the factory. Again, and no panty twisting intended, what's the best way to proceed in the bowl/guide area on a 308 head?
 
I myself, Can not answer porting questions since I am not a porter.
In general, I could suggest a course of action if I have done it
Myself or know from a reliable source that a certain something works.

Read the thread I did, sorry I replied I am. I'll leave your thread now. I see
To la k the experience you seek and the attentiveness of all your threads
 
Again, it was never my intention to piss in anyone's Post Toasties. My apologies if I've offended.

Now that that's settled, I have an idea for a cheap way to visually study the oddities of the 308 port, and maybe answer my own question. As soon as I'm not working 14-16 hours a day seven days a week I'll give it a try and maybe post it here so others trying to work with these heads will have some much needed answers.
 
I got those heads but the MP ones based on the 308 castings, forgot the number. Anyhow I run the small port intake, the old Dual Quad intake for the 273 engines. Never dyno it but seem to be making loads of power. The ports are small but short and some are straight to the head. Got both airvalve doors removed from the 500 cfm Carters now, it kicks harder then any Holley 750 dp carb I ever used...no bogs either, I believe the smaller ports help keep the air speed fast
 
What I'd REALLY like to know at this point involves the shape of the guide in the bowl. If the flow does indeed have spin around the axis of the valve, induced from the curved guide, should the teardrop shape be angled more in the direction of the swirl? Or equal on both sides like a regular port, or just left flat on top as cast?
If the air in the bowl is turned properly and the area behind the valve (the cylinder) does not shroud flow, the air moving through the open intake valve will form a tapered conical shape with the valve head as the large diameter and the cone tapering towards a three dimensional point within the cylinder. (that tid bit's courtesy of Smokey Yunick) Unfortunately the guide, the approach to the valve, and bore diameter in most "normal" V8s restricts that cone development. The swirl port is a way to try and use that energy to minimize the negative influences of the design. If the head had a straight approach (like the Cleveland Ford and Hemis for example) then a simple teardrop streamlines without hurting anything. But when the guide is a long boss and curved, its' my belief that the "seam" of the tear drop should continue the line formed by the angle of the boss through the guide. But as I said, I wouldnt do any more than you have on your heads.
The guide's shape in the bowl looks more like a rudder to me, with the narrow straight areas and deep hollows on each side. The flat area on top looks designed to induce tumble. Odd combination of shapes even for the factory. Again, and no panty twisting intended, what's the best way to proceed in the bowl/guide area on a 308 head?
My understanding is the guide and boss is a rudder to the airstream along the roof of the port. The tumble the design induces is not within the port. It's in the chamber as the air passes the seat and valve and it's designed to re-suspend fuel that has dropped out of the airstream. The shapes are designed to create higher or lower pressure areas inside the port in order to "steer" the air to where it can do the most good. GM took a little different approach with the bowl in the Vortec heads but it does the same thing. Again - Noting the work you've already had done - Don't touch the guide boss or do any more than slightly round off the corners in the existing bowl. There is work that could be done in conjunction with more complete port work, larger valves, a better valve job, and chamber work. But I feel it would only hurt performance with what you have now. Just my opinon there and I'm sure there are those who will disagree.
 
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