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20B's performance margin diminished due to AI
hey, it's minus 10 degrees today so i thought i'd throw up something to chew/war on...
maybe some of you haven't visited the Auxiliary Injection Section. since we all run turbos here in the FD section we all run into hp limits in the form of KNOCK. if we have modded our FDs some of us add racegas at $10+ per gallon, hit the dyno and crank up the boost. whoopie! 550 rwhp. neat. the only problem is back in the real after/dyno world we pull up to the pump and fill our tanks w 93 octane gas. horsepower looks a bit different on pump. one bar, 400 or so hp. that's old school. enter AI. the equation looks alot different with the help of a little alcohol. hp on the street is no longer KNOCK LIMITED crank on the boost til your turbo is maxxed out on the street. if your tuned right you will be looking at less than 10 on your PFC knock log!!!! this changes everything including your choice of turbos but that's for another thread. getting back to this thread... so you can make 550-600 rwhp on the street w 93 pump and your motor will show better metrics (lower knock etc) than 93 at one bar w no AI. many of the guys doing the 20B route did it for more hp. 400 on the street left something to be desired. add 50% more rotors and you add approx 50% more power. 600 or so rwhp. the difference between a 400 rwhp FD and a 600 rwhp FD is not easily imagined. in order to appreciate the additional hp you literally have to be holding on to the wheel of a 600/FD. w 600 rwhp you can make the car go sideways at over 100 mph in 4th gear. easily. at a certain point you have to ask yourself.... do i really need rwhp i can't use? 20Bs have made 1200-1500 rwhp on methanol. 13Bs make 1000 rwhp on methanol. my point is you can NOW (w AI) relatively easily make 600 rw w a 2 rotor w AI. so exactly where are you going to be able to USE the additional hp above 600 that the 20B provides? of course for the 10 people on this board that want to really run in the 9s i fully understand. but if you are one of the 100 or so that have done the 20B swap for a dual purpose FD... ok, if you did it for the unique-ness i am with you 100%. if you did it for the performance advantage, uh, there's no advantage in useable performance V an AI 2 rotor. further, while it sounds pretty easy to do a 3 rotor conversion it is not. you run into clearance issues w the steering rack and end up with a bumpsteer nightmare. bump steer is death. stock car/circletrack/shorttrack guys set bump steer w a feeler gauge! that'show important it is. the last 20BFD i did a bumpsteer curve on had a half inch of bump steer at 2 inches of bump. yes you can set the engine back and do a few things... you can fix just about anything, but you better not move the rack. to those who have, show me your plotted bump steer. i am not anti 3 rotor. it can be done right. i am just saying that the real world margin of performance is now close to nil. don't know about AI? we have lots of threads in the section. read up. howard coleman |
There is a kit on the market now that has 0 bump steer. The rack remains in the same place with no issues whatsoever. This is the route I opted to take...
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The only thing that worries me about AI is what if the system fails, or one runs out of water/meth... For that reason, Im planning on tunning my car for 15-16lbs and then adding water injection just as a safe guard. If i run out of water ill still be reasonably safe. (if i can do that without sacrificing much HP)
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Originally Posted by ArmenMAxx
(Post 7849482)
The only thing that worries me about AI is what if the system fails, or one runs out of water/meth... For that reason, Im planning on tunning my car for 15-16lbs and then adding water injection just as a safe guard. If i run out of water ill still be reasonably safe. (if i can do that without sacrificing much HP)
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I will second this as I'm making 560rwhp 470fl.tq @ 26psi w/ alcohol injection on 93 pump gas and yes the car will go sideways in 4th or 5th.
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Peak numbers aren't everything. It's the overal powerband that will make the most difference in performance and what wins races. Howard you of all people should know that. Now Howard is dead on when you consider it's really hard to match the hp per dollar figure of a 13b set-up with AI. Personally I would rather have 600rwhp on straight pump gas with no other sub system to rely on.
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Powerband is a tricky topic because it really depends on the class you want to run in. Is it nice to have a wide power band? , sure but is it a must have to win, no.
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Very interesting commentary Howard. After my 4th 13B engine I decided to go with the 20B. It has been a huge project that was not what I had imagined. It was not nearly as easy as I thought, and problems continue to pop up. The original final product is something to be proud of, but when I see Ernie, and others making up over 750 with their 13B it does produce some doubts about what type of performance advantages this engine actually produces. I am hopeful that it will RELIABLY produce 550-600 on low boost.
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I dig it Howard...
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To me 13b's can make plenty of power, and go plenty fast. So can a 20b but should produce power more reliably. Everyone says it all comes down to the tune, Ernie for example has a great setup producing gobs of power and his motor is still running great the last I read. 400hp is more then enough to do anything you would like, I couldn't imagine having 600+ just seems overkill to me. Everyone has theyre own wants though. I would be happy to be able to do 500-600HP but I wouldnt want it, 400-450 is more then enough for me!
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please do keep in mind i am not knocking 20bs. i am merely making the point that w alcohol and 2 rotors you can make 550-600 rather than 400 on pump.
that fact changes the equation between a 20b and 13b. and of course you can AI a 20B and make 800-900. please let me know what it is going to do for you beside totally frying your tires. it is also possible to build a 20b FD right. it is also possible to totally screw up the front geometry. gordon's car has always sounded especially neat to me and knowing gordon it is built right. it should be super. hc |
Very interesting, I was thinking on going 20B but now this changes a lot....AI here I come.....
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Yes KAI! You install yours, and then I'll do mine...HAHA! How often has an AI system failed and blew someones motor anyway?
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im doing my 20b swap as soon as my car gets out of the body shop and i was thinking that if i did ai then i could take my 20b to 600whp with tons of reliability from what you are saying. but then again im thinking i might use e85 fuel too so ai might be pointless in that case any suggestions?
20b streetport t88h |
dyno graph/runfile for NA 20b
Hi, quick question: do you have a copy of a dyno chart for your NA 20b? Even better, if you were on a dynojet, do you have the dyno runfile(s)? I've never seen an NA 20b dyno graph... I have to do some searching :) I always thought an NA 20b to be the motor Mazda should have used in the FD in the first place too.
Kind of off topic... do you have any media of your car (videos, track videos, etc.)?
Originally Posted by gmonsen
(Post 7851710)
If I can "wax philosophic" for a moment... I picked up my first new FD in March of 96 and drove it to PFS where Peter did like "Stage I, II, and II" and I had a "360 hp" Mazda Rx7. This was not true, but some crank hp estimate that might have been 320 hp, but it was very fast. Then, he upped me to Hitachi T25's for maybe 350 rwhp and later he took me to my first single turbo, which we won't get into much, for maybe 375 rwhp. Later, I changed my single turbo setup and normally drove with about 425 rwhp. People just kept making more and more power. I first tried water injection in 1999 and thought it held the secret to much greater reliability and power. Now, Ernie makes 750 on a single turbo no problem.
Like many, I have no idea why I would want more than 400-500 or so horsepower in a street car. I am completely comfortable that a 20b NA can produce that reliably and with instant response, wide powerband, and linear power for control. I am dumbfounded that Mazda planners and management didn't go with the 20b for the car to begin with. I think it would have made this car a winner. The 20b at 375 hp would have cost the same to put in, if not less. If would have made more power and been way more reliable. Gordon |
instead of all this AI stuff, why dont people just add a wet shot of nitrous and run lower boost?
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Originally Posted by gmonsen
(Post 7851710)
Like many, I have no idea why I would want more than 400-500 or so horsepower in a street car. I am completely comfortable that a 20b NA can produce that reliably and with instant response, wide powerband, and linear power for control. I am dumbfounded that Mazda planners and management didn't go with the 20b for the car to begin with. I think it would have made this car a winner. The 20b at 375 hp would have cost the same to put in, if not less. If would have made more power and been way more reliable.
Gordon |
Originally Posted by 1wide7
(Post 7849500)
I dont have a system yet But from what Ive read they have warnings for clogged AI injectors and low fluid lights so if your system malfunctions you know it! Howard can elaborate furthur
http://www.youtube.com/watch?v=rTeKQPUnzCc |
Originally Posted by jacobcartmill
(Post 7855706)
instead of all this AI stuff, why dont people just add a wet shot of nitrous and run lower boost?
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This all sounds good, and of course I can see the logic behind it.
I just have one question: All you guys making 500+WHP why aren't you running the rear tire set-up to hold that power?.... Im talking about wide fenders, and rear tires in the 335 range... Or does it all come down to the short gearing of the FD (in comparison to 500hp supercars)??? |
Originally Posted by gmonsen
(Post 7851710)
The 20b at 375 hp would have cost the same to put in, if not less. If would have made more power and been way more reliable.
Gordon But I think that the new rx-7 should have a 3 rotor version of the Rensis, as clearly it could make some good NA hp! ;) |
Originally Posted by gmonsen
(Post 7851710)
I am dumbfounded that Mazda planners and management didn't go with the 20b for the car to begin with. I think it would have made this car a winner. The 20b at 375 hp would have cost the same to put in, if not less. If would have made more power and been way more reliable.
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The problem with 20bs is the expense of getting one, building one, custom installing one, etc. Plus when you need parts, some of them are very hard to come by and very expensive (shaft, fat intermediate, tension bolts).
Even to do an NA 20b, most people are looking at around 10 grand to import one, rebuild it with port work and repair any issues it had when it came off the boat, then get it installed, a custom computer to run it, and tune. Even if you go carb, a custom carb manifold setup is not cheap at all. Having built a couple of 20bs, it does not seem they are as structurally sound as a 2 rotor. It is clear the 3 rotor was an afterthought, they just did what they had to in order to tack on another rotor...it was not really a project designed from the ground up, like for instance the first versions of rotaries, or the renesis. Nonetheless they seem to hold up very well most of the time but I would always be a lot more comfortable with a 13b under the hood that I know I can get parts for at a reasonable price within a few days' time no problem should the need arise. |
You guys make a lot of good points re: 20B vs 13B and "streetable" power. I was thinking about going 20B NA once my engine throws in the towel, but it would be nice to drive one to see the real difference.
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