Lasse wankel

I am in progress to build a 20B for a customer inNorway. The engine is streetported and the intake flows for 311 hp N/A which i think translates to around 650hp at 15psi boost (the turbo is a T-88 Greddy) 20B exhaust sleeves are removed and FC-sleeves is installed. Flow numbers for stock 20B housings are 94 cfm@10' Now with a good streetport job and Fc sleeves it flows 152cfm@10' My question is now is it wise to do a 4 or 6 pin doweling to the engine to withstand the abuse the engine is gotta see? It should be dynoed on arolling road (Rototest of Sweden) and be mounted in a street driven JC-Cosmo. Any input would do me happy!

RETed

I think it's overkill for "just" 650.
If the engine doesn't detonate, it'll stay together.


-Ted

Evil Aviator

I think you aren't going to quite make 650hp with those numbers because you can't just double the horsepower when doubling the pressure ratio. Once you consider the added heat from producing that boost, and raised BSFC caused by the richer AFR, the output will reduce. Depending on your intercooler, I think you will get somewhere between 500 and 600hp at 15psi, which is plenty. The Pettit Banzai runs about 550hp at 15psi with no problem, and I don't think it has any doweling.
http://www.pettitracing.com/

I have the 5 full-sized Banzai pages saved at my website if you would like to download them to your hard drive and read them.
http://www.geocities.com/evilaviator/banzai1

Thank you for the flow numbers. It is always nice to have tangible data.

Lasse wankel

Thanks for the inputs! Come to think of it that a 13B REW motor can handle 500hp on 2 rotors w/no doweling so a 20B has less stress per housing true or? If i can stay under 50C degree after the intercooler and have an exhaust temp of max 900C i think i will make make near 600 hp if no detonation occurs. What octane rating do you guys suggest if i boost 15-18 psi? Ignition timing i think the engine can take a little more than a 500 hp REW becausse of the spread of 3 rotors. Unfortanately the engine is not going to be dynoed until next Spring.

t-von

iTrader: (8)

Not neccessarily. The 20b produces alot more torque at a much lower rpm than a 13b will. The increased low end torque that is produced by single turbo setups is the reason extra dowel pins are used(snap torque). The snap torque can break your e-shaft. Also the length of the 20b (having more plates) makes it a little easier for the housings & side plates to shift under these stressfull conditions. Thats why the earlier 20b engines always failed. Mazda found ways to strengthen the engines on the later models. Think about it this way, isn't it always harder to eat a double meat hamburger compared to a single meat hamburger. The double meat will always fall apart first.

now

iTrader: (1)

ok on the topic of doweling has anyone tried to do it
yourself? I was thinking of setting up to do them but
have not had time to work on this stuff at all as of late

matt

mmaragos

Low end torque of single turbos? I see many examples of the twins having more torque down low, or is "low" 4000+ RPMs?

I didn't think there were significant changes to the block structure/dowelling between production years for the 20B. What changes were made?

Interesting example with the double meat burger, but I don't think it has significance here. Unless you are putting some "special sauce" between your rotor housings.

There are plenty of single turbo 13Bs producing good power (450+ HP) without dowelling. I would invest my money elsewhere instead of extra dowelling on a 20B with a goal of 650 HP.

t-von

iTrader: (8)

Ooops I guess I should have said hp & torgue. I got that info from 3rotorrx7.com. Derick and the builder claimed that the single turbo he installed on this 20b put down a ton more power down low as compared to the twins. As a safety precaution thats why they did the extra dowel pinning to keep the engine from twisting.

Quote:

[i]I didn't think there were significant changes to the block structure/dowelling between production years for the 20B. What changes were made?

See this thread, specifically the 2nd page

https://www.rx7club.com/forum/showth...hreadid=108091

Quote:

[i]Interesting example with the double meat burger, but I don't think it has significance here. Unless you are putting some "special sauce" between your rotor housings.

Why wouldn't it have any significance? Haven't you ever had a really tall sandwich that had tooth picks in it to help you keep it together? Because of the extra length, I think extra dowel pins are neccessary for the 20b regardless of how much hp it's putting down. Mazda should have over built the engine from the start. The 20b being a longer engine as compared to the 13b has more of a chance of twisting within itself. Look at the LeMans car, I beleive it had extra dowel pins and it was NA.

Quote:

[I]There are plenty of single turbo 13Bs producing good power (450+ HP) without dowelling. I would invest my money elsewhere instead of extra dowelling on a 20B with a goal of 650 HP.

To each his own. I feel if you're going to spend the money on something like this and put down that much power, why not dowel pin for the added safety. At least if you then decide for a hp increase, the engine will already be setup for the abuse. Anyways a dowel pinned 20b and proper tuning makes it damn near bullet proof.

rxman720b

If you are going to ever think about doing the single turbo, PIN the motor. It is easier to do it while you are in there. When i went single turbo, about two weeks later I twisted the motor and jammed an apex seal. So now my motor is pinned and street ported and also has 3mm apex seals. Now it is very strong. I even used rotary truck corner seals. Now it is near bullet proof as t-von stated.

rxman720b

BTW those are real flames coming out of my tail pipe on my avatar pic. Better to run rich than lean!

mmaragos

Thanks. Now I remember reading about how Mazda strengthened the 20B (from its original config). Total brain fart on my part.

Definitely food for thought, no pun intended, about the dowel pins. The "special sauce" comment in my first post needed a .

Now you guys have me thinking about something I never really thought there was a need for.

now

iTrader: (1)

I guess no one has tried to do this yourself.
or is keeping it a secret, as soon as i have time i will
be working on this and posting my results

matt

RETed

Uh, that's one of the most absurd things I've ever heard.&nbsp Ever seen the center key?&nbsp Is it larger than the one in the counterweight?&nbsp If your "snap torque" theory holds true, wouldn't it shear the rear key in the counterweight first?

I'm thinking more along the lines of e-shaft flex.&nbsp When the e-shaft is modular in the center, the e-shaft flex would make the joint very weak.&nbsp I doubt torque is snapping them apart.



-Ted

t-von

iTrader: (8)

I can take constructive criticism, but that was unneccessary. This is a friendly conversation/debate. By looking at all your post, I would naturally assume that you have a ton of info on this subject. If I have said something that was way out of line, by all means please help me understand it for future referance. NO FLAMES ok



Don't take the phrase "snap torque" to seriously. That link I posted above has info on how the e-shafts were improved over the differant engine runs. They were made stronger. Torque had something to do with it.

now

iTrader: (1)

the changes that mazda made were more to do with changes
to the housings than changes to the e-shaft.
I have looked closely at both early and late e-shafts
and i couldn't see any differences at all, but the changes to the
housings once you know what you are looking for are very noticeable.
as for snap torque, i have heard the term before but don't fully understand it.
what i do know is the e-shaft can start to get a wobble/flex at
rpm and high torque that can allow the rotor enough
movement to hit the rotor housings

matt

Jeff20B

iTrader: (13)

Hey now, which housings are you refering to? I've got an early engine #756. If I purchased a later 80mm cast iron housing, is that all I'd need to handle more power?

now

iTrader: (1)

all 4 iron housings were strengthened
matt

t-von

iTrader: (8)

Thx, I needed the backup

Lasse wankel

I have 2 20B and building 1 for a Norwegian guy. I just wonder in what areas the strenghtening is made on the iron housings? The rear oil regulator on the rear housing is it a 65 psi or 100 psi?

crispeed

Most of it was done in the dowel area on all the iron housings.
I was also told that the area in the big housing around the stationary gear was strengthen. I cannot confirm this because I've only opened the newer motors so far. I'll be openning one of the earlier motors soon and I will do a comparison when it happens.
The strength of the e-shaft also is questionable by some individuals above 1000 to 1100 rwhp. I'll be finding that out in the next month or two!
I've seen the destruction done after the e-shaft broke on one of these individual's motor. The shaft, gear, rotor and housing were totaly destroyed. It happened twice before trying an after-market shaft which put an end to the problem.

Lasse wankel

Thanks Chrispeed for the info! I have chamfered the area around the holes on the big intermidiate housing it was very sharp and not tapered.

t-von

iTrader: (8)

Hey guys check this out. This may cure the dowel pinning problem. Click engine services to see for your self. I've already sent an e-mail to see when they will be available.

http://www.xtremerotaries.com/



Edit: So far they only have a kit for the 13b (20b to be out shortly). Its $434.50 in Aus dollars. After converting to US I got $306.04. Then there's the bore and tap kit thats needed. It's the same price. So thats $612.08 to have this done to a 13b. I figured the 20b kit will cost around $800.00 due to the extra studs that will be needed.

now

iTrader: (1)

would have been nice to have seen a pic of these items.
the problem with studs that fit tightly in the housing holes
is when you get a bit of corrosion you will never get the motor
apart again.
I know someone else who is using a pin / stud in 4 areas
and the tension bolts in the rest, I feel that the expansion
of the housings is not being properly allowed
for when using studs, the factory tension bolts allow
for even expansion.
the floating dowels that come from the
factory are the right idea just more or longer ones
would be better, i am looking into long thin dowels that
could be used in the tension bolt areas along with
the tension bolts which will still allow for the
expansion the the engineers designed for.

matt

t-von

iTrader: (8)

Hmmm I never thought about it that way. I guess I'll have to ask them that question about expansion. Also you wouldn't have to worry about corrosion if you used distilled water in your coolant system. This is what I use. I pulled my motor a little while ago and had no signs of corrosion. The drained coolant was extremely clear. Anyways if I could get a consideral amount of life out of my future rebuild using these studs, I wouldn't worry about the block sticking.

now

iTrader: (1)

the stock dowel pins are in oil areas which makes them
come out in most cases easily, but when dowels are
put into the tension bolt area they are in coolant.

funny things start to happen when steel and aluminum
are stacked and are in contact with fluid.

if dowels or studs are put in the tension bolt holes
they will have to have a tight clearance to be doing
any good, its in these tight quarters that the effects of even
the slightest electrolysis, even with a good quality coolant
and "distilled" water will only slow down the effects of electrolysis.
the people that i know of using dowels in the tension bolt
areas use lots of anti seize compound in an effort to allow for
disassembly, the zinc in the anti seize compound acts like a
sacrificial anode.

I feel that with a little thought before putting dowels in the
tension bolt areas will result in a stronger motor but also
a motor that will be disassemble able.

matt