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Hey guys, i was in process of tearing down my intake when i realized i was looking at 4 ports instead of 6 which to me looks like someone bored out during latest rebuild. Im guessing they were aiming for a cosmo type setup. Unfortunately for me i just bought an RB intake manifold for a weber and already bored it to 51mm. Im in it now so imma just wing it in hopes for good results. Has anyone ever heard of this type of porting? Any input on this would be greatly appreciated. I traced the gasket onto new manifold, looks wonky to me, going to try and trace engine ports tomorrow. Not sure if this is a 6 port ported to 4, 4 port cosmo, or turbo 2 engine.... the old gasket lines up pretty well on the new manifold overall. 13b s4 n/a full bridgeport
That did start life as a 6-port and from the picture looking into the port it looks like it still is. Looks like the just ground out the two individual runners into a single one but still splits into two separate ports deeper into the runner. As for how well a setup like that works. Someone else will have to chime in.
That did start life as a 6-port and from the picture looking into the port it looks like it still is. Looks like the just ground out the two individual runners into a single one but still splits into two separate ports deeper into the runner. As for how well a setup like that works. Someone else will have to chime in.
Thanks Dak for confirming that for me, my mind was going nuts for a while after looking at that and looking up other version gaskets and comparing. Anyone else know pro's/cons of porting done this way? The runners in my RB intake are open inside anyways so at least will be an easy port job for that. Looking at 13b gaskets the 90-94 Cosmo looks like what they were aiming for. Guessing this is gonna change jetting in my 51 IDA carb. Hope to hear from some more of you guys, thanks. -Seth
Siamese 6 port-
Dave Lemon of Mazdatrix was instrumental in banning early opening streetports and developing a 6 -> 4 port streetport and carb for SCCA E Production racing.
Dave wrote online that in developing the porting he had to work many dyno hours and fabrication at getting intake and exhaust tuned lenths just right to manage to get peak torque under 10,000rpm.
Which was a goal because the limited mods allowed to rotating assembly in E Prod (basically just balancing and oil pressure allowed I believe).
You indicate your engine is bridgeported.
This wil change the intake and exhaust lengths required.
Also, bridgeporting may bring peak torque RPM down simply by virtue of being able to flow more air at the port face and with the help of exhaust overlap- so helping support velocity in the port runners at lower RPMs.
In any case, due to your porting and aftermarket intake manifold any tubular headers exhaust should help your power much more than on a stock port engine.
Siamese 6 port-
Dave Lemon of Mazdatrix was instrumental in banning early opening streetports and developing a 6 -> 4 port streetport and carb for SCCA E Production racing.
Dave wrote online that in developing the porting he had to work many dyno hours and fabrication at getting intake and exhaust tuned lenths just right to manage to get peak torque under 10,000rpm.
Which was a goal because the limited mods allowed to rotating assembly in E Prod (basically just balancing and oil pressure allowed I believe).
You indicate your engine is bridgeported.
This wil change the intake and exhaust lengths required.
Also, bridgeporting may bring peak torque RPM down simply by virtue of being able to flow more air at the port face and with the help of exhaust overlap- so helping support velocity in the port runners at lower RPMs.
In any case, due to your porting and aftermarket intake manifold any tubular headers exhaust should help your power much more than on a stock port engine.
Thanks Blue, was hoping to hear something like this. I have a racingbeat header to presilencer that I'm in process of throwing on to what I believe is stock y pipe out. Hopefully that's enough on exhaust end, if I knew all of this before ordering parts I would have grabbed a true dual header. When it comes to the rb intake manifold I'm just gonna try my best at port matching, I would think that I should leave some tunneling in there for a swirling air effect and mostly just bore the very end of intake? Figure minimal first cuts guessing be the best bet for porting. Not trying to waste $400 with an immediate hack job haha. Thanks again, great post, very informative. -Seth
Wouldn't work as is? Could there possibly be a benefit air flow in the divided the intake, maybe straightening of the flow? Maybe D shape where they are close?
Seems if only the secondary's were bridge ported the divider might help velocity in the port? Every time I see a port like this I wonder why they didn't just leave the divider and D shape where they're close.
i wonder that too. the thing is the velocity (fps, feet per second), vs flow (cfm). its clear that the bigger should flow more, but you don't get the expected power increase, and B the torque peak moves WAY up in the RPM band
why? probably because velocity goes from ok, to zero....
so i'd be temped to leave the intake alone too, just to try and keep the port velocity up. unfortunately the only way to test it is to try it, and then hog out the intake and try again....
Awesome input guys. I unfortunately did this before I read this and don't really have funds for dyno results. I decided to go with the runners in the intake and go with this design hoping maybe air gets some swirl in? Fingers crossed but figure I'll try it and feel it out. Here's some pics. Do you guys think that air flow with tunnels in intake is a good idea (8design) or should I just bore it to completely open? I thank you guys for helping me threw this. I still gotta fine tune the ports but this is rough draft they are pretty close. Just winged it
Looking threw some books i forgot i had stored away i found these two pages referring to intake porting. book is Street Rotary by Mark Warner. Great info in there think i bought it off racingbeat years back. Would be interesting to hear from someone with one of these Godzilla sized secondary ports like i have. within a few weeks hopefully should have everything together on build and will post updates with running situation.
Cheers,
-Seth
That did start life as a 6-port and from the picture looking into the port it looks like it still is. Looks like the just ground out the two individual runners into a single one but still splits into two separate ports deeper into the runner. As for how well a setup like that works. Someone else will have to chime in.
There was no torque peak as far as I could tell. It kept pulling harder the higher you revved it, up to about 9000rpm. It made close to the same peak power as my bridge port.
Emphasis on PEAK. The bridge port makes peak torque around 3500rpm and it just keeps sailing from there, you can shift it anywhere and it would still be good. Very broad, tractable, easygoing power band. The opened up 6 port, if torque peaked AT 9000, you'd have to upshift at exactly the right speed, probably around 14,000rpm if it can make power that high, to get best acceleration, since the ascending torque curve meant that no matter when you shifted you would fall into a hole torque-wise.
I took it back apart and stuck it on a shelf.
I would not port that any further, if you pull it apart for any reason, chuck those parts and replace with Turbo II. The 6 port end housings close way too late to make any decent low- or mid-range torque.
You could epoxy fill the top of the port, to the face if it's still supporting the trailing end of the leading side seal, leave a slight gap if it doesn't, and then reshape the port.
I had, at one time, figured out plugging the 5th and 6th ports with cast iron. The port itself is CNC machined and I have a CMM plot of the port, it wouldn't be hard to make an insert to fit a modified port and match the round 5&6 ports. I had planned a hole through it on the centerline and then plug the round hole with a cast iron round with a turned pilot. One could have it go into another round plug dropped in the very back of the port with a hole in it. JB Weld it all in place at assembly.
Or, I've always wondered how that aluminum solder/weld would work for such a thing.
From looking at these two pictures, especially the top one. I'm not convinced that this engine isn't still a six port. Looking further up towards the actual ports leading into the engine it looks like the secondary and aux ports are still separated rather than being "hogged" out into one big port. Of course, with the engine together it is hard tell. If one had a borescope/ endoscope you could turn the engine over by hand until the rotor is in a position that has the intake ports fully open. Then run your scope in through the primary ports and look at the secondary ports on the other side.
There has to be a strip of metal there to keep the side seals from falling in.
The 4 port/6port refers to the number of runners, not windows. Bridge ports are not referred to as 8 ports
That's not the way I have always understood it. I always understood it as the opening in the side housing is what is referred to as the port. Not the opening where the intake bolts to. Mazdatrix's page on porting the 6-port makes it sound this way as well. 84-92 6-Port Intake Porting - Mazdatrix
All their talk on porting makes it sound this way. Your right we don't call a bridgeport an 8-port even though there are eight openings. Either way the point I was making is he thinks the openings in the front and rear iron have been opened up to make one large port like Mazdatrix talks about in that link. I thought ther was a picture of that port, but I guess there isn't. Looking down the runners I'm not so sure that's what he has.
Ive awoken the big dogs of the forum!!! Man am i happy to hear from you guys, ive read hours of great info and learned so much on here from forum reading and your input on things. Im going to try this setup with intake in hopes i save a little bit of mid rpm torque. still gotta shave a tiny bit to match ports completely to my best judgement. Im excited to put it all together and see how she runs. Just ordered the final parts (fuel pump conversion) and am looking to start putting parts on soon. In my thoughts of air flow i think the 8 design might be beneficial for air flow, im no scientist or professional by any means but makes sense in my head of how things operate with a little resistance. And the engine porting was done prior to me when the engine was rebuilt and since is in car im just gonna run with it and leave engine ports as is and adjust intake porting as needed (fingers crossed my idea works well) Will update as soon as possible with results. sadly gotta break engine in so guessing gonna be really stumbly in low rpm, gonna try to keep her around 4k for the first 500 miles, cant wait to try out higher rpm range later when can do so. I have another engine i plan on building in future and plan on going turbo 2 setup, but for now gonna see how this one goes. So this is my final design for intake im running with. Thanks again guys for more great input, i wouldnt have made it this far without this forum and the people involved in it.
That's not the way I have always understood it. I always understood it as the opening in the side housing is what is referred to as the port. Not the opening where the intake bolts to. Mazdatrix's page on porting the 6-port makes it sound this way as well.
The port is the tunnel, the port window is the opening in the side of the housing.
OTOH, people also call side housings "irons" or "plates", which always struck me like people who call axle bearing retainers "wedding rings" or their sister "wife"
I had planned a hole through it on the centerline and then plug the round hole with a cast iron round with a turned pilot. One could have it go into another round plug dropped in the very back of the port with a hole in it. JB Weld it all in place at assembly.
i followed your post up to here, then got a little lost. can you explain what you mean, please?
i followed your post up to here, then got a little lost. can you explain what you mean, please?
The 5 & 6 ports are round holes with a port cut into them from the face, easy geometry except for the port in the face itself. The top and bottom of the cut almost tangents the center of the round hole, make at least the bottom tangent and make top parallel, then a plug can be made the shape of the face cut with a round back the same as the hole diameter. A hole can be machined on the port hole centerline in plug so that another plug, round, and coming in through the intake side, with a reduced diameter would then go through the other plug to keep it from ever wanting to come out.
There' enough round past the port put another, more disc shaped plug in, this could have a hole in also really locking it in. The JB Weld it all together after test fitting.
My idea was then you could make the secondary ports whatever shape or however big you wanted to. There would no water around the top of the secondary to worry about hitting. it's also a way to use what is basically thought of as a junk plate for performance I hope this helps you understand.
From thread I linked above. Epoxy in port, with through holes to epoxy on the other side, to keep it locked in place.
Actually, since the engine is all apart now, I can take better pics if you would like.
The main reason I did it was my 6 port manifolds did not have separated ports (one unknown Holley, one Atkins side draft), and I always hated the port runner shape, and all of the flow-killing surface area of having two separate runners, so.... let's experiment a little with low-value parts.
10-23-23, 06:49 PM
