rarson

Hey guys, I've been thinking about this, maybe some of you can help. I noticed Guru finally has their 20B e-shaft on their site now, so this has gotten me thinking more.

First of all, it seems like nobody generally turns their 20B past 8500 rpm, and with good reason. But since I've been contemplating an N/A build, I was wondering how one would go about building a 10k rpm 20B. I'm not trying to just pick an arbitary number, but I'd like to get a significant amount of revs out of it since the intake and exhaust will likely be up to the task. So if I were to limit it to 9800 rpm, or 10,200 rpm, or 9850 rpm, whatever. You get the point.

Looking at Guru's description, I'm a little disappointed by the lack of information (or maybe I'm just not interpreting it well). For one thing, it doesn't specifically mention whether the shaft is lighter than a stock shaft like they mention for the 13b app (though I would assume it is). Secondly, it doesn't clearly state that it suits high-rpm apps, like the 13b does, so I'm wondering if the advantage to this shaft is as great as is with the 13b shaft. Do you guys see any reason why it would offer an advantage for a high-rpm engine?

I don't see too many problems with revving the 20B. I understand that the longer e-shaft will have greater flex, probably an advantage for using the Guru shaft. I also understand, at least I think I do, that the motor could have twisting problems at high rpms. If I understand correctly, doweling would likely prevent that problem.

Are there any other things I should be thinking about when it comes to revving the **** out of a 20B?

mcfly

I have been reading that the guru shaft is no more stronger then the stock shaft out of the abcd series 20b.

Of course i wont judge it as i have not tried it first hand.

t-von

iTrader: (8)

I believe the main advantage of the Guru Shaft is it's center bearing that will keep the shaft from flexing. Preventing flex is a must if you want stratospheric revving. With the extra bearing, I see no reason a 20b couldn't rev as high as a PP 13b provided you have adequate clearancing and oil pressure.

Falcoms

Also, if you're going N/A, I would assume that running a super lightweight rotor set from racing beat would keep rotating mass down, and therefore limiting flex, as well as get you to your high RPM's faster. Having the whole rotating assembally (counterweights, flywheel, rotors, e-shaft) dynamically balanced is also a must for high rev's like that.

DMRH

Been to the Guru shop in Melbourne to sus out his operations.

Mighty impressed..............

Watched the shafts get made up from seriously high strength steel billets. Each billet weighs around 80 - 90kg from memory

The precision put into these shafts would put Mazda's production compromise's to shame. The strength is also a "no-compromise" affair too. Thats why they are near twice the price of a Mazda shaft.

Get a 4-bearing 20B engine made up & there is no reason why 11k rpm cant be a normal event.

I know his 3-bearing 13B engines are doing 13k rpm with reliable operations.........

REgards

rarson

Well, I estimated the Guru shaft to cost ~$3000-3400 USD, shipped. Which I personally think is a good price.

I wasn't sure if it did actually have the extra bearing, so thanks for answering that for me guys.

I'm also thinking about the Kiwi-RE 3-rotor kit. The cost is not that much more than the Guru shaft, and the engine would be shorter and likely lighter. I don't see much point in having the large intermediate plate if I build a peripheral port engine. Of course, I'd have to buy other engine parts but at the same time, I wouldn't have to buy a 20B.

Rxmfn7

iTrader: (4)

Exactly what I have been thinking of doing as well. Would like to shoot for 400WHP N/A. Keep us (me) updated on what you decide to do. I cant make up my mind as of lately.

ReZ311

iTrader: (4)

Why not throw some RX8 rotors in there with hardened stationary gears and make sure your whole rotation assembly is balanced for high RPM usage?

Also, you need to make sure the oil jets on the E-Shaft are lined up with pre-rx8 rotor bearings as the oil groove windows don't line up with RX8 babbot bearings.

Rxmfn7

iTrader: (4)

Correct me if I am wrong, but I dont believe anyone has of yet made any more power with the renesis 10:1 rotors over the S5 N/A 9.7:1 rotors in N/A 13B applications. In fact, there seems to be a significant power drop with the rene rotors.

KeloidJonesJr.

iTrader: (8)

Hi-comp! That's what teh GT RX-7 is made of...WIN!!!

ReZ311

iTrader: (4)

If you read the title of this thread, then you would consider the weight of the renesis rotors. I chose the renesis rotors because of the lighter weight and design to spin 10,000 rpm. Perhaps Racing Beat or Mazdatrix could lighten them up even more if need be...

DMRH

GURU sell a normal 20B type shaft that uses the 3 bearings. If you want a 4 bearing engine. They will custom make it to your specs.

The Kiwi-RE kit isn't actually a Kiwi-RE kit. They are the "middle man". The actual kits are made by "Precision engineering" also in Auckland & can be purchased direct from them. However, Kiwi-RE will be happy to sell you the Precision kit wth their own mark up attached..........

Since the last time I checked. Precision engineering dont make a 20B shaft. Their 3-rotor shafts use a centre bearing 13B centre plate making them shorter than a regular 20B.

REgards

Rxmfn7

iTrader: (4)

No reason to be a dick about it.. I was just poiting out a potential snag when thinking of the renisis rotors.

calculon

iTrader: (29)

DMRH,
got a website for Precision Engineering? I googled it and nothing came up right away.

rarson

Thanks for the info! Yeah, I kinda figured there'd be a mark up attached. The short 20B is kind of the direction I'm leaning to.

Yeah, actually I was thinking about that. Here's the thing: the 9.7:1 rotors are heavier in stock form. However, going by the numbers listed on Racing Beat's web site, the lightened 9.7:1 rotors are lighter than the lightened Renesis rotors. I've been thinking about which would be better: lighter rotors, or the higher compression. When it comes down to it, the weight difference is very small, as is the compression difference. However, I believe the Renesis rotors in stock form are pretty close to the lightened 9.7:1 rotors, and I'm SURE they are MUCH cheaper. So I do think that the Renesis rotors are almost certainly a better (reasonable) choice.

Yeah, I was wondering the same thing.

I really appreciate all the good responses in this thread, thanks guys.

rarson

Oh, one more thing. The smaller plate of the Kiwi (or rather, Precision Engineering) kit leads me to believe that there wouldn't be enough room for the regular side ports, hence the thickness of the production 20B plate. So I figured that the plate would be suited for a peripheral port application. Anybody know about that? I'd be willing to build a peripheral port engine, as I know quite a few people (especially the Aussie guys) have street driven them, but I'd likely go rather conservative on the ports. Ideally though, I'd have a sideport engine.

Rxmfn7, 400whp would be a very nice number to hit (that's actually about all I'd need, I think) and I'd be happy with that. Considering GtoRx7's car has already made 350, I'm thinking a few steps more and we'll be there easy. I have to warn you though, this is a project that I'm looking at for the long term. I'd love to see more people try the N/A 20B setup though!

calculon

iTrader: (29)

i had the same question regarding the side posts so i emailed them and they said that they do have plates that allow you to use side ports and they are the same thickness. the wording was a little ambiguous, but i have the email saved at work. i'll do my best to remember to post it tomorrow. they did say that they have more side ports running around than peripheral ports using those kits.

rarson

Cool, thanks for that info.

ReZ311

iTrader: (4)

10.0:1 is not much, but every little bit helps in a 3 rotor engine with 9 combustion chambers.

buju2003tt

ok guys so the kiwi-re built three rotor kit can also be used as a side port engine would u be able to bridge port one of those short block's from kiwi-re

GtoRx7

iTrader: (5)

You are going to go through everything to think about that I did. It will most likely lead to one answer. I was going to go with the short 3-rotor as well, 1 1/2 inches shorter, 25lbs lighter, who wouldnt want that? But, you will find that a few problems with it, first is price. It will cost you over $3800 just for the parts from Kiwi. Next you have to buy three 13b rotor housings, (3) 13b rotors, purchase fuel injectors, stationary gears, oil pump and counterweights. A 20b is ave. $3800 for the whole longblock, parts that are able to be sold for profit, and help make the n/a a reality. Sell the turbo rotors, sell the intake, sell the turbos, sell the turbo mani ect. The other problem like you said is that the center rotor of a kiwi will have two primary ports. The "solution" would to run a baby bridge port using only one port per rotor, or cap them all off and go full P-port. Both in my book arent fun except in a full track car. 400rwhp on side ports alone, unless bridge port, may not be possible.

If you are running a full p-port motor the Rx-8 rotors provide a good amount of gain from torque increase. On a side port motor, almost no gain will be had other than a lighter rotating assembly.


There is no 13b center plate that can have room for a large secondary port, so you must use only one port per rotor, and use all primary ports, which are very little. Or Maybe half-*** it and port the primary to secondary size, but the runner will still be 1/3 the size and not flow even at all.

rarson

Well, see that was my considerations. The Renesis rotors wouldn't be lighter, at least in their lightest forms from RB, but they WOULD be higher compression ratio. So what would be better? A higher CR or lower rotating assembly?

Yeah, that's why I figured that they were all p-port. So I'm thinking maybe a sideport using the Kiwi plate wouldn't be ideal...

GtoRx7

iTrader: (5)

Yes, if doing sideport, a 20b will school a Kiwi, if doing p-port, the kiwi would be a obvious advantage.

fritts

iTrader: (5)

I always wondered would a PP 20b have a better idle and be more "streetable" than a 13b because of the 3rd rotor? I would think the 3 extra combustions would smooth out the low end. Let me know if I'm off in my thinking.

GtoRx7

iTrader: (5)

It is better, the extra mass, and faster firing 120 vs 180, makes it idle smoother as well.
If it is "streetable" would vary from opinion!