J-port & Turbo - can it be done?
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Joined: Aug 2001
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From: Bay City, MI
Nope, bad idea. There's way too much overlap between the intake and exhaust. Overlap is a brief moment of time when both the intake and exhaust ports are open at the same time. Think about what that would mean with pressurized air coming through the intake, much of it would go right out the exhaust before it had time to compress and combust. I believe a street port is about the largest you want to go with forced induction.
Hunting Skylines
Joined: Apr 2001
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From: Brisbane, Queensland, Australia.
Originally posted by metalliman
Nope, bad idea. There's way too much overlap between the intake and exhaust. Overlap is a brief moment of time when both the intake and exhaust ports are open at the same time. Think about what that would mean with pressurized air coming through the intake, much of it would go right out the exhaust before it had time to compress and combust. I believe a street port is about the largest you want to go with forced induction.
Nope, bad idea. There's way too much overlap between the intake and exhaust. Overlap is a brief moment of time when both the intake and exhaust ports are open at the same time. Think about what that would mean with pressurized air coming through the intake, much of it would go right out the exhaust before it had time to compress and combust. I believe a street port is about the largest you want to go with forced induction.
Large ports (pp, bridge) are one of the keys to making big power whether it's n/a or turbo.
Scoot pp turbo... 700hp.
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From: Auckland, New Zealand
Originally posted by metalliman
Nope, bad idea. There's way too much overlap between the intake and exhaust. Overlap is a brief moment of time when both the intake and exhaust ports are open at the same time. Think about what that would mean with pressurized air coming through the intake, much of it would go right out the exhaust before it had time to compress and combust. I believe a street port is about the largest you want to go with forced induction.
Nope, bad idea. There's way too much overlap between the intake and exhaust. Overlap is a brief moment of time when both the intake and exhaust ports are open at the same time. Think about what that would mean with pressurized air coming through the intake, much of it would go right out the exhaust before it had time to compress and combust. I believe a street port is about the largest you want to go with forced induction.
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Got Boost?
Joined: Feb 2002
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From: Watertown, MA
Overlap is bad for light throttle/low load fuel consumption, for emissions It also will make the power band shift a bit higher, and is great for top end. The more overlap you have the more sensitive to back pressure the engine becomes.
Not sure I'm buying this one, at least not overlap alone. Radical porting increases VE, even at fairly low RPM (2500 rpm) over stock, that is what spools turbos. The overlap is just a consequence of porting.
Overlap equals faster spool up
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Joined: Jun 2003
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From: Minden, NV
In theory; theory and practice are not the same. If they were there would be no distinction and no one would ever try testing anything. That and 'theory' would just called be 'the way'.
Fatboy, more overlap causes more exhaust gases to go into the intake charge, but it also causes more air/fuel to get sucked out the exhaust. Being as the rotaries already dump copious amount of fuel out the exhaust the large overlap just adds to the rally style anti-lag like action that happens-and allows these little tiny engines to spool big-*** turbos
Fatboy, more overlap causes more exhaust gases to go into the intake charge, but it also causes more air/fuel to get sucked out the exhaust. Being as the rotaries already dump copious amount of fuel out the exhaust the large overlap just adds to the rally style anti-lag like action that happens-and allows these little tiny engines to spool big-*** turbos
Rotary Freak
Joined: Feb 2001
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From: Okinawa, Japan
Thanks Epi.
Too many times people overthink issues. Even though it seems that something should not work if your looking at it on paper, many times in practice it does work. For certain applications of course. The people with these "big-*** turbos" needs the spool up. However, on a mild daily driver the overlap would be less than ideal.
Too many times people overthink issues. Even though it seems that something should not work if your looking at it on paper, many times in practice it does work. For certain applications of course. The people with these "big-*** turbos" needs the spool up. However, on a mild daily driver the overlap would be less than ideal.
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From: SoCal
The difference is clear!
Here's a dyno compression of 13BREW stock port compared to JPort. The set up is non-sequencial boosted to 10 psi. The difference is clear! 
STOCK PORT: 224RWHP 202FTLBS
JPORT: 270RWHP 221FTLBS
STOCK PORT: 224RWHP 202FTLBS
JPORT: 270RWHP 221FTLBS
Last edited by rx720bt; Jul 17, 2003 at 10:01 PM.
Banned. I got OWNED!!!
Joined: Mar 2001
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From: lebanon
How much more proof do you wan that it cant work !
Overlap is bad, dont anyone waste your time trying it
Stick to std ports please, Mazda knows best.
I REPEAT DONT WASTE YOUR TIME, INFACT IF POSSIBLE FILL IN YOUR SECONDARY PORTS TO RESEMEBLE THE OPENING TIME AND CLOSING TIME OF THE PRIMARIES, SEE HOW GOOD IT GOES THEN
Overlap is bad, dont anyone waste your time trying it
Stick to std ports please, Mazda knows best.
I REPEAT DONT WASTE YOUR TIME, INFACT IF POSSIBLE FILL IN YOUR SECONDARY PORTS TO RESEMEBLE THE OPENING TIME AND CLOSING TIME OF THE PRIMARIES, SEE HOW GOOD IT GOES THEN
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From: Minden, NV
on a mild daily driver the overlap would be less than ideal
And ya, definitly, mazda knows best
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From: Auckland, New Zealand
Originally posted by RICE RACING
How much more proof do you wan that it cant work !
Overlap is bad, dont anyone waste your time trying it
Stick to std ports please, Mazda knows best.
I REPEAT DONT WASTE YOUR TIME, INFACT IF POSSIBLE FILL IN YOUR SECONDARY PORTS TO RESEMEBLE THE OPENING TIME AND CLOSING TIME OF THE PRIMARIES, SEE HOW GOOD IT GOES THEN
How much more proof do you wan that it cant work !
Overlap is bad, dont anyone waste your time trying it
Stick to std ports please, Mazda knows best.
I REPEAT DONT WASTE YOUR TIME, INFACT IF POSSIBLE FILL IN YOUR SECONDARY PORTS TO RESEMEBLE THE OPENING TIME AND CLOSING TIME OF THE PRIMARIES, SEE HOW GOOD IT GOES THEN
What about this stuff you said off Aus-rotary...I wish this **** would get solved so we have some ground rules.
Originally posted by RICE RACING
There is NO DIFFERENCE between most n/a PP's and turbo PP's, This overlap thing is getting very tiring now! the sort of crap Fast Fours and Rotary editors and contributors used to crap on about in their infinate wisdom
Go on nopistons.com and ask "Judge Ito" about turboing std PP n/a housings, he will give you an example of a guy who did it with GREAT success.
Your more than welcome to come over and look at my housings
If you want to bag others who have got it to work then I suppose I wont stop you either ?
There is NO TECHNICAL reason why it wont work ! If you stop and think that some of the most efficient engines are two stroke diesle turbos with unbelievable overlap (very sensitive to back pressure!!!!) you will see that the amount of overlap in a PP is nothing !
There is NO DIFFERENCE between most n/a PP's and turbo PP's, This overlap thing is getting very tiring now! the sort of crap Fast Fours and Rotary editors and contributors used to crap on about in their infinate wisdom
Go on nopistons.com and ask "Judge Ito" about turboing std PP n/a housings, he will give you an example of a guy who did it with GREAT success.
Your more than welcome to come over and look at my housings
If you want to bag others who have got it to work then I suppose I wont stop you either ?
There is NO TECHNICAL reason why it wont work ! If you stop and think that some of the most efficient engines are two stroke diesle turbos with unbelievable overlap (very sensitive to back pressure!!!!) you will see that the amount of overlap in a PP is nothing !
Last edited by EScalade; Jul 20, 2003 at 09:14 PM.
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From: S.A. Texas/Tokyo Japan
Here is a pic of my ports. Opening is stock but the closing have been moved up. Both primary and secoundary close at the same time. (Hope the pic come out.) The one thing I did notice about the small bridge on the secoundary is the the a/f ratio reads leaner now. If I try to add more fuel the car gets slower so I think I am close the the correct a/f for the motor. Also running 8 injectors. Each intake runner has it's own primary injector. 11.4#et at 127.89mph with 1.9# 60 foot times. 2720 lbs car. Car idles at 1200-1400rpm.
chuck
chuck
More overlap isn't neccesarily bad or good. It can be either/or but it depends on what the intended use of the car is.
More overlap blows air out the exhaust?! That is the biggest load of crap I've ever heard. If the engine can't keep enough air in the combustion chamber since so much goes around it, how can it develop enough pressure to spool the turbo? It couldn't. When the engine spins fast enough the inertia of the incoming air is enough that it stays moving in the proper direction. If this wasn't true then why do high overlap engines (n/a) attain greater than 100% volumetric efficiency at higher rpm's? It is at this point the turbo has enough pressure on the exhaust wheel that it creates boost. Once a little bit of pressure is created, the boost helps make more and it does it at a faster rate than a low overlap engine. Turbo lag from idle may be a little bit slow but once the rpms are higher and the gas pedal is punched, hold on! Punch it at freeway speeds. What lag?! As I said the inertia of the air keeps it moving in the proper direction when it gets to the combustion chamber. If we are talking about a roots style blower then yes it would blow some air out the exhaust port. It would also blow air into the combustion chamber and make some fantastic top end power.
I do detect the sarcasm in many people's responses but this is to dispell the false rumors spread by the serious people.
More overlap blows air out the exhaust?! That is the biggest load of crap I've ever heard. If the engine can't keep enough air in the combustion chamber since so much goes around it, how can it develop enough pressure to spool the turbo? It couldn't. When the engine spins fast enough the inertia of the incoming air is enough that it stays moving in the proper direction. If this wasn't true then why do high overlap engines (n/a) attain greater than 100% volumetric efficiency at higher rpm's? It is at this point the turbo has enough pressure on the exhaust wheel that it creates boost. Once a little bit of pressure is created, the boost helps make more and it does it at a faster rate than a low overlap engine. Turbo lag from idle may be a little bit slow but once the rpms are higher and the gas pedal is punched, hold on! Punch it at freeway speeds. What lag?! As I said the inertia of the air keeps it moving in the proper direction when it gets to the combustion chamber. If we are talking about a roots style blower then yes it would blow some air out the exhaust port. It would also blow air into the combustion chamber and make some fantastic top end power.
I do detect the sarcasm in many people's responses but this is to dispell the false rumors spread by the serious people.
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