Who has a nice mild street port template for 12A?
 

Peeps,

I am rebuilding a 12a and like to port it. I have seen the Mazdatrix and the Racing Beat templates on their websites, both look a bit large. Anyone have a reccommedation of one they have used? Same for the exhaust port template. the car is going to be my daily driver and dont want to sacrifice driveability for a few more ponies at the top end.

Thanks!!!

I'd have to recommend '74 spec. It's the best port for daily driveability and great power. You don't really loose much in the low end and gain a lot in mid to high. You can also keep using a stock carb, saving some money. The ports respond very well to carb mods though, and are compatible with stock or very free flowing exhaust. '74 spec ports are all around excellent performers and by far the most popular port in my neck of the woods.

Someone needs to sell a '74 spec template. I made one out of paper, which I used on several engines. Then I used the plate in an engine recently so the paper template is the only one I have.

I might get access to another '74 plate at some point, and could make templates, but for now all I have is the one paper template and I'm hanging on to it. I don't want to make a copy of a copy because it would be inaccurate.

Here is a thread detailing a set ports ported to '74 spec and some other cool stuff. https://www.rx7club.com/forum/showthread.php?t=539579

Thanks Jeff. I think i will end up keeping ports stock since I cant find a decent template that is truly a mild street port. Eventually I want to make a 4 port 13B so I can play with porting then...

I think the RB template is pretty mild... you should get that

You got it all wrong. You can make even a monster streetport streetable by using smaller venturies/jets.

Wouldnt that be like training for a marathon if you are going to race in a 10K?

I'll revisit that one. Have you used it?

nope but just in case you wanna be competitive later on. So whats the point of going with a ported engine if you cant enjoy it. :rlaugh:

Jeff,
if you mount that paper template on a sheet of 4 grid, or any other grid (and specify) and copy it, I can make dimensioned autocad prints of it that would be exact replicas. That way you can have some spares. PM me if you're interested in doing it and I'll shoot you my email address. I'll send a set out to you and you can compare to make sure its good.

Send me one if you do!

^^+1

Im using it. Im porting right now. Does not change the timing THAT much.

Jeff, knowing how much respect these hooligans have for you and your opinion (not me, i don't respect nobody but mom and barry goldwater) i'd say we should stand and deliver. I do, however, trust your judgment and if you say so then the 74 spec should be made available to the public, if possible.

I'd like to see a more streetable peripheral port. Like a 42mm intake port placed at just the right spot so to minimize exhaust gas dilution but not go too far into the power stroke.

Yes
 

Yes i like the sound of that i can use one.

2nd, so maybe my dreams can come true :)

Wow a Barry Goldwater reference, gotta love it... I gotta read up on the runner up... Didnt a youg Hilary campaign for him... [Drifting off subject...]


[QUOTE=glewsRx;7410919]Jeff, knowing how much respect these hooligans have for you and your opinion (not me, i don't respect nobody but mom and barry goldwater) i'd say we should stand and deliver. QUOTE]

Come on Jeff, you know I'm getting ready to rip into my old girl. Something like this could sure be useful. :)

Down has the gauntlet been thrown.... (read in lord of the rings voice)

I took the S model for a 1st drive yesterday and wow those '74 ports are perfect. They have low end, mid and high up to 7k. You can't beat that for the street. I don't care if you have power up to 8k if your low end is missing. Have fun driving that daily. lol

I don't have access to any '74 port plates at the moment. If I did, maybe I could start making paper copies and selling them on the forum. It's easy to use paper to mark ports. Simply use a Sharpie, fill in the area above the port on the iron so it's all black, then lay the paper on the plate using dowel pins to align it, then take a center punch, leather punch, nail or whatever you have that's handy and pointy, and follow the edge of the port. Lift the paper and you have a small visible line through the ink. Port up to that and smooth the transition from runner to port. Also chop down any casting flash and harsh 90° edges. Then finally take a broken stone bit (garnet) in your dremel and spin it at the slowest speed to add a roughened finish to the port (press hard to slow it down even more). That's what I did in the 12A in the S model. It has a little over 2k miles and it freaking flies.

I totally agree. Without low-mid-range torque it isnt a pleaseant DD just because you are putting up an extra 20HP @ 8K

Unfotunately, I call that it a total bullshit.

Whatever works for you Wacky. I personally dont like to have to over-rev at coming off every light in a DD. Just not worth it to me. Now for a weekend/special occasion car...

Jeff, I'll lend you one of my unmolested 3B plates to copy from if you want.

Wacky, I've been driving my GLC with a large streetport daily for a while now. It sure is fun when you get on it, but just driving it around in traffic I sometimes wish I had a little more down low and that I was getting better than 13 MPG. Keep in mind that this is in a car that weighs some 500 lbs. less than an FB. Big ports are awesome if you have another car to drive daily, and it was worth the trade-off for me, but I can sympathize with someone wanting a little more low-range push and not wanting to completely trash their gas mileage.

I'll agree with Jeff that '74 spec makes a really nice mild port. It keeps your powerband within usable ranges and isn't a chore to drive stop-and-go. Combine it with a nice exhaust and carb, and you'll be very happy with the results.

As I said, you guys got it all wrong. It doesnt matter if its a monster streetport, bridgeport and p-port. Tuning (use of smaller jets and venturies) will make anything possible.

Port size and location determines intake velocity and rpm at which torque and hp peaks.

Venturi sizes are used to fine tune, but not radically change the above.

A monster streetport makes peak hp at, say, 9000rpms. Put smaller chokes in the carb (36mm for example) and you'll increase intake velocity and fuel atomization at the carburetor end. Some more torque at a lower rpm, and ^ MPG.

But the large intake port will inherently have lower velocity. And smaller chokes limit the amount of air that can enter the motor and it'll reach maximum airflow below 9000rpms. Revving over 6500rpms would make no more horsepower because the small chokes are flowing the maximum amount of air they can. All you're doing is spinning the motor.

Smaller ports would work much better with the smaller chokes. Want more HP? Increase both moderately thus the term street port.

The key is to match venturi size with port size for the best performance over the motors powerband.

Exactly. No amount of tuning on a big-ported engine will prevent reversion at low RPM or reduce overlap. You should choose the port that best suits the type of driving you do, then tune to match the port.

I wonder what is his definition of "unstreetable

Wacky, you're one in a million.

I hope so. If not, this forum may crash twice a day. And thats a very nice old school song...:rlaugh:

lol what I meant was when you use smaller jets and venturis to try to make up for large ports, you're left with an engine that has little bottom and low power up through the rev range. That's not very fun to drive.

Ask Percent how his GLC ran when we tried the Hitachi with 20mm venturis and 92 primary jets, and then tried the other Hitachi with 22mm venturis and 105 primary jets. Ask him which carb he likes better on his rather large ported 13B, and I'm sure he'll tell you the bigger of the two.

Nobody thinks of the obvious
 

I can't believe so few people have done what I do on all the engines I build for street use - I do a minor cleanup of the primary and exhaust ports and then use the RB street port template for the secondary intake ports. This gives driveability and fuel mileage virtually the same as a stock motor, but with a significant gain in full throttle performance. Look at the relative size of the primary and secondary throttles in the carb, and the logic of this scheme is obvious. My 12a is done that way, but with an RX-4 carb and RB header, got 130 hp to the wheels, which is at least 150 hp at the flywheel. My peak horsepower is at 7,000, compared with 6,000 for a stock motor.

then what is ]unstreetable:confused:

Your cars. Kidding. :)

stilettoman, I did a mild port on the primaries and a large streetport (I think it's RB sized) on the secondaries in the GLC. The exhaust ports are a little bigger than T2 spec. It's using a '76 Cosmo carb which has the large 22mm venturis. The air bleeds were already excellent at 60 and 90, and I upped the fuel jets to 105 pri and 160 secondary. That carb is completely maxed out, and it is the same size as the earlier '74-'75 REPU and RX-4 carbs, except this one has a smaller vacuum secondary jet allowing faster open time (according to Klaus42 who knows about these carbs) of either 60 or 90, instead of 120 of the older carb. I also removed the spring from the vacuum diaphram thing so they pop open easier. I've tried larger fuel jets (117, 170) but they always have trouble. I can't go any smaller on the air bleeds.

As I said, this carb it totally maxed and yet it is still inadequate for the engine. Now if the ports were smaller, let's say '74 spec primary and mild streetport secondary with smaller exhaust ports, the carb would match the engine a little better. For example my REPU has '74 spec intake ports all around and the exhausts are the same size as the GLC's (to correct some stupid upside down D ports) and I'm using the '74 carb with 105 pri, 155 sec, and 60 and 90 air bleeds. This carb has a 120 vacuum secondary jet with a removed spring. Its secondaries don't hit as hard as the Cosmo carb, but the primaries have decent power in such a heavy vehicle with a stock 30 pound flywheel. If I threw in a light steel flywheel, like in the GLC, it would be a more accurate comparison.