Porting the engine
10-31-07, 07:10 PM
#1
Porting the engine
hey guys i have a 85 gsl - se with a 12 a sitting in it (motor was swapped in due to blown 13b). I am looking to get the Extend Port for it, and was wonder is it worth keeping the 12a and porting her, or should i just invest in a 13b and take it from there? And no, i want no turbos in my car, i want to go N/A. Is investing in the 12 a worth it?
Thanks....
Thanks....
11-01-07, 01:06 PM
#3
I don't believe in huge ports for the street so much anymore. If you can retain some low end, you're better off. A port size that I've found works great for this is the stock size Mazda used in '74-'75 engines. It's half way between an extend port and a stock '76-'85 port. I call it the '74 spec port. I've used it on a few engines and have had better results than large street ports.
11-01-07, 01:14 PM
#4
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If you've got a good 12A core, use it and port it to '74 spec like Jeff says. I've personally felt the results of those ports on a 12A, and let me say they are impressive indeed.
11-01-07, 04:12 PM
#6
depends on how far you plan to go. i know you said you plan to stay non-turbo, so the choice is really yours. if you enjoy your 12A (obviously the car's already setup to run with it), then port it, keep it and drive. i'd personally go 13B, but 12A's are fast and fun, too.
11-04-07, 01:33 AM
#7
great information guys. the 12 a is practically brand new. I bought it straight from mazda 3 years ago (got it at a nice deal) and has around 60,000 Km's on her. I guess my power goals would be between 200-230( At the wheel). As of now i have just about every mod you can do without touching the engine and carb. As far as this "74 spec port" goes, will a shop know what that is if i ask them to do that for my engine? I take it that type of port will allow for more low end torque vs a extnended port?
Thanks.....
Thanks.....
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11-04-07, 02:25 AM
#8
great information guys. the 12 a is practically brand new. I bought it straight from mazda 3 years ago (got it at a nice deal) and has around 60,000 Km's on her. I guess my power goals would be between 200-230( At the wheel). As of now i have just about every mod you can do without touching the engine and carb. As far as this "74 spec port" goes, will a shop know what that is if i ask them to do that for my engine? I take it that type of port will allow for more low end torque vs a extnended port?
Thanks.....
Thanks.....
11-04-07, 09:55 AM
#11
Yeah, shutup kid.
My car makes 200rwhp and 230tq with a stockport 12a and TII turbo at 14psi. If you want to stay n/a you're not gonna make that kinda power unless you bridgeport it.
11-04-07, 10:30 AM
#12
I don't believe in huge ports for the street so much anymore. If you can retain some low end, you're better off. A port size that I've found works great for this is the stock size Mazda used in '74-'75 engines. It's half way between an extend port and a stock '76-'85 port. I call it the '74 spec port. I've used it on a few engines and have had better results than large street ports.
Thanks, Mike
11-04-07, 09:59 PM
#14
THere is definitely a market for it. People who actually plan on using their car as a DD dont want a car with no low end torque for the benefit of a few extra ponies at 7K RPMs.
11-05-07, 06:11 AM
#15
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c'mon jeff. what are you waiting for? Just get that port template mad up and make us all happy. Every thread about porting a 12a end up with you saying "the 74 spec port is the best port there is, a total cream dream, you drive it and women on the street throw their panties at you, and it starts raining gold and jellybeans. Too bad nobody but me gets to have one. Its really nice though, guys."
11-05-07, 12:18 PM
#19
In case you're wondering how a paper template can work, it's actually quite easy. You mark the closing edge of the port with a sharpie, lay the paper over it, take a sharp pointy object and scribe the shape through the ink, carefully following the edge of the paper. Lift the paper and there is your line.
The nice part about '74 spec ports is exhaust porting is optional. The US-spec '74 engines had the same port timing as US-sepc 1st gen 12As. You can either leave them stock or delay the closing edge a few degrees. I've tried it stock and slightly delayed and both performed excellently.
The nice part about '74 spec ports is exhaust porting is optional. The US-spec '74 engines had the same port timing as US-sepc 1st gen 12As. You can either leave them stock or delay the closing edge a few degrees. I've tried it stock and slightly delayed and both performed excellently.
04-10-10, 01:38 AM
#25
The 74 ports work on 4 port motors. Not a 6 port.
Pics are of my motor with 74 intake ports with a port cleanup and side seal clearancing but otherwise stock intake ports. Exhaust has obviously been ported.
https://www.rx7club.com/showthread.p...+%2Bstreetport
I bought the RB template and marked it on the plates with a sharpie so you can compare size. Not much bigger but it's all in the bowl and angles. And runners, good power to be had enlarging the runners. And later in the thread pics of it plated to RB specs. See for yourself.
The 74 ports was a nice motor that made ok power but nothing earth shattering. With 41mm chokes in the dellorto it really really revved. Low end sucked with the 41s. With an IDA and 38mm chokes low end was good but needed more top end thus the motor cracked open and porting. But made better overall power and throttle response than the Dellorto with 39's. The Weber IDA rocks and us very good at moving air and fuel.
I had a 12a with a larger than RB template port and it made damn good power but more up high. Drove that 12a motor to work and in the field for 4 years 25,000miles a year. Very drivable with a punch.
If you really want a 74 template I could do one on cardboard or something on the cheap. It's great for daily driving and better than stock. Better MPG than the streetports, it's all a tradeoff really.
Pics are of my motor with 74 intake ports with a port cleanup and side seal clearancing but otherwise stock intake ports. Exhaust has obviously been ported.
https://www.rx7club.com/showthread.p...+%2Bstreetport
I bought the RB template and marked it on the plates with a sharpie so you can compare size. Not much bigger but it's all in the bowl and angles. And runners, good power to be had enlarging the runners. And later in the thread pics of it plated to RB specs. See for yourself.
The 74 ports was a nice motor that made ok power but nothing earth shattering. With 41mm chokes in the dellorto it really really revved. Low end sucked with the 41s. With an IDA and 38mm chokes low end was good but needed more top end thus the motor cracked open and porting. But made better overall power and throttle response than the Dellorto with 39's. The Weber IDA rocks and us very good at moving air and fuel.
I had a 12a with a larger than RB template port and it made damn good power but more up high. Drove that 12a motor to work and in the field for 4 years 25,000miles a year. Very drivable with a punch.
If you really want a 74 template I could do one on cardboard or something on the cheap. It's great for daily driving and better than stock. Better MPG than the streetports, it's all a tradeoff really.
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