Well guys I am getting my whole rebuild idea set up. I have decided to go with the Mazda Apex Seals and Springs and FD Corner Springs. But here is my question. I have a S5 T2 Engine and I am going to give it a good size streetport and I still will run the stock turbo w/ a fully ported wastegate. I have a FCD, Cosmo 20B Fuel Pump, and I am thinking of getting 1600cc secondaries and I also have a SAFC2, and all the Defi Link guages w/ controller. Will the 1600cc secondaries be to much? I also have a 3 1/4in Turboback exhaust, and I will also have a ACT Street/Strip clutch and ACT 12lb flywheel. All emissions have been removed and the OMP system has been removed as well...I will run Idemitsu Premix. So I have the chance to get some really nice S5 GTU rotors. I think there compression is like 9.5.1 but thats what I want to run in my T2 engine. I know running these rotors will give me a good amount of power but will also give me less room for error in tuning. Is there anything I would have to do to run these rotors? WOuld it change anything in my engine assembly by putting these rotors in b/c I know that they are lighter than the S5 T2 ones that have a 9.1 Compression. Any help would be greatly appreciated I am just ready to get this buildup started and get bck on the road. Thanks
Mike

 

1600's will absolutely way way way too much with the stock computer. With what you're wanting to do, I highly recommend ditching the Mazda system and going to a standalone. I don't mean to be rude or condescending, but that is a ticking time-bomb setup waiting to explode.

B

 

yup, i wouldn't go over 820cc injectors with a stock ECU, the MAF won't be able to flow enough to provide the flow to necessitate that huge of injectors.

 

Yeah I figured 1600cc would be to much....so I will get at least some 750cc High Impedence. But mainly would using these GTU rotors give me trouble in this buildup if tuned correctly. I have a SAFC2 and a Air/Fuel Guage. Would any assembly steps change if I used these lighter rotors?
Mike

 

Your turbo rotors are 9.0:1 CR are the same weight as any non-turbo S5 rotor with a 9.7:1 CR.

I don't recommend doing this unless you know what you're doing.


-Ted

 

So the rotors...weigh the same...Correct? Why would you advise I not do this? I would have a suffiecient amount of FUEL so detonation would not be a problem. I am not arguing with anyone I just am trying to figure out if this is worth me doing. The GTU rotors are from an auto car....(first off did the GTU come in an auto option?). I really can get a good deal on these very nice GTU rotors and I may get them depending on what you guys let me know. Is there anything special I would have to do to use these rotors?
Mike

 

Hi Mike,

Detonation isn't the problem; pre-ignition is. The stock ECU is fairly aggressive with its ignition timing, running a zero-degree split under varying loads. The higher compression rotors translate into less "tolerable" room for tuning. Fuel isn't the only part of the equation (and no, you wll decidedly _NOT_ have enough fuel for the higher load points)... spark timing is, and I believe it's considerably more critical than fuel delivery capabilities.

Get a standalone. Dump the stock EFI system, the FCD, and the S-AFC.

B

 

I see....I understand now. I wish a damn Standalone was cheap.
Mike

 

it cheaper than a new engine. ask me how i know

 

No.
It's more an ignition timing problem versus a fuel problem.


-Ted

 

Seven dreams if I were you and seeing how you cant' wait to race ever car on the road and I was building a engine I would use rotors from a 87-88. You can boost more on pump gas with the s4 rotors.

 

This is very true Bukwild....but tell me something. I know the S4 T2 rotors have a lower CR and the S5 T2 rotors have a higher CR....but honestly if I used the S4 T2 rotors how much power would I be sacrificing from using these heavier rotors. I have heard things like the lighter S5 rotors give you better throttle response and slightly more power...but i do know the S4 rotors can handle alot more boost. Which option is better if I want a good strong fast car that can take a little detonation and not just pop on the very first time. Although I dont want to experience any detonation...it may happen.

 

It really depends on your goals. If this is just going to be a moderately powered street car that you want to just have some fun with and not have to worry as much about popping your motor, I would go with the S5 TII rotors. If you plan on running a monster turbo with high boost ( > 15 psi or so) at some point, then you can go with the lower compression S4 TII rotors if you're worried about detonation. As for the S5 NA rotors, the car will have better off boost manners (better throttle response, increased power), but the tuning will take on even more importance. Personally, I wouldn't recommend it if you're not going to run a standalone and have it professionally tuned by someone experienced with this setup.

Long story short, if you want a good balance between off-boost power and detonation resistance, you probably want to use S5 TII rotors. Especially if you're running the stock ECU, SAFC, and the stock turbo. Of course people have run NA rotors safely with stock ECU, etc...but S5 TII rotors are the best compromise for your needs, and is the simplest route IMO.

True, but he's planning on using the stock turbo so running high boost really isn't an option...

 

Thanks Ultradef for the write-up it was very informative. I guess I will go with the S5 T2 Rotors. I may still get those N/A rotors and just keep them around to have for another engine I may build. Can you tell a difference between two same engine buildups...one using S4 T2 rotors and the other using S5 T2 rotors. Will the S5 rotor engine make more power and be faster? Thanks
Mike

 

on my motor I am running now I had Landers use mazda racing 3mm seals and kept the s4 rotors because I plan to run 15lbs on 93. I am going to look into water injection this summer to up that to 20lbs on 93. I didn't really start off planning to build a 500hp setup but you kinda end up progressing that way the longer you go. But its always best to build the best motor you can while you are doing a rebuild. If this motor goes I am going RE with REW exhaust ports built to the hilt.

 

You're welcome.

To answer your question, yes an engine built with S5 rotors will make more power than an otherwise identical engine with S4 rotors (everything else equal - i.e. boost, mods, etc.) due to the higher compression ratio.

 

"everything else equal - i.e. boost, mods, etc.) "

well I am not sure I agree with that. Their are 2 forum members dropping down well over 500 on s4 rotors, 17-20lbs on pump gas.

If you have a turbo that has a efficiency range of 20-28lbs what good is it to have a engine that is only safe to run 15lbs?

 

Very true. BUt my recommendations are based on the assumption that he will be running a stock turbo, which he stated in his first post. We all know the stock turbo isn't very effiecient past 12-13 psi, and intake temps start skyrocketing. I datalogged my intake temps with my Haltech on a couple runs around 1 bar on the stock turbo and intercooler, and my temps jumped to over 200 degrees within seconds. That is just asking to pop a motor. If he plans on upgrading the turbo at any point, that would be an entirely different ball game.

 

yeah I wouldn't even have a motor built if I was going to run a stock turbo. stock = sucks

 

I will only be running the stock turbo for a couple of months then it will be upgraded as well as a FMIC and standalone. Which leads me to belive i need S4 T2 rotors.

 

First question...are you using a standalone EMS or stock ECU?
If you're stuck with the stock ECU, don't mess with higher CR's.
You're asking for trouble.

Second...is this a race car?
If not, don't bother with the higher CR rotors.
Leave them for the racers who can use them to the fullest.
I understand the temptation to get the "best", but in this case you're playing with fire...literally.
I understand there are owners who are running turbo'd 9.7:1 engines, but the majority of them are pure race cars.

Sure, the 9.7:1 rotors are going to give you a little more power (down low), and respond better, but it isn't worth the risk on a street car.
One slightly bad tank of gas and the engine goes up in smoke...


-Ted

 

I have the stock ECU right now and the car will be a street/strip car...not a RACE CAR. SO I guess it makes more sense to go with the S4 rotors. I dont want to blow an engine again. Its certainly not fun and my 7 has been off the road to long. I just thought that the S4 T2 rotors would slow me down...but if the difference is minimal I guess its much safer to go with the S4 T2 rotors. Thanks
Mike

 

it'll be a JACKSTANDS car if you use higher compression rotors and bigger power on the stock ECU.

 

Jackstands has seen enough of my car....its my turn agian.