Northwest FD3S

I am currently installing a T78 turbo on my 13B, does the engine need to be dowelled? Or will i blow my engine if it is not dowelled?

milkman2k52

I don't really know much about dowelling but I think it is more a matter of how much torque your engine is going to be making. And from what ive read so far it seems it just moves the breaking point somewhere else....

someone more knowledgeable will respond soon im sure.

Northwest FD3S

I believe that a stock rotary engine is somewhat dowelled already. I keep hearing that i need to dowell my engine from a local shop. Someone, anyone on this forum with a T78 turbo running 12-17PSI must have some info on how there car is running and if the engine has been dowelled????

milkman2k52

i think the general consensus is that it is not needed unless you are making over 500 ft/lbs which i dont think you will be doing at 17 psi.

DBS

I have seen a car put 565 lb/ft to the wheels and it wasn't dowelled. I have seen plenty of RX-7s with T78's that aren't dowelled and they have never had any problems (with dowell related issues). For your application, I wouldn't worry about it.

Northwest FD3S

Thanks for the info. I didn't think you could twist the housings much if the hp was under 500.

es

Dowell pinning helps to reduce the twist of the housings, but this can be done other ways as well. RTV the sandwich bolts to reduce harmonic vibrations, & increase the rotor to end plate clearance. The late model (I think it started in '97 but I donno for sure) FD rotors have an increased side clearance from the factory.

Pettit really pushes pinning, as well as 3mm apex seals. Many people don't agree with either of those tecniques. I'm one of them, but that's only worth about $.02 since I'm not a professional engine builder. It's just a hobby for me...

Badog

Hey,

I thought part of the reason of pinning was addressing the expansion and contraction of the whole chamber under boost and keeping things consistently lined up. Even when running >20psi boost?

Tony

es

Yes, but IMHO much of the housing squirm is caused from E-shaft flex & collisions between the rotor & all of the housings vs: chamber pressure. Pinning is like strapping the motor together instead of trying to reduce the harmful harmonics. (a bandaid vs: stitches)

I really don't have enough experience with high boost motors to have anything more solid than an opinion formulated from Rice racings comments, & info from the Racing Beat rotary guide (which basically backed up everything Peter had told me)

Then I found more proof when I got my brand new rotors. Mazda revised the FD rotors for increased side clearance. I posted pics in the rotary performance section of the revised rotors, but that thread got trashed in one of the forum crashes (It didn't get much attention anyhow for some reason). Anyhow, that is 3 sources that put very strong emphasis on rotor clearancing, & I haven't found that much strong evidence to pin a motor yet. All I know is Pettit suggests it. But they also push 3mm apex seals which is something I disagree with.

AJatx

iTrader: (1)

Dowel pinning the engine (or increasing the size of the current dowels or adding more dowel pins) will help with high torque application as well as high boost.

Depending on what year of rotor housings used, the older generation housings tend to have a weakness near the oil filler neck. During high boost/high torque application, the stress seems to crack the housing in that area.

crispeed can give you some good advice on dowel pinning the engine to reinforce that area of the rotor housing.

A lot of the serious drag racing engines are pinned in one way or another. If you're making about 500rwhp, you're getting close to the edge with some of the older generation housings (s4 housings for sure).

If you're just installing a T78 and plan to run about 1 bar of boost or play around with tuning it for 20psi with race gas, then I wouldn't worry too much about dowel pinning the engine.
It's a nice assurance, but you'll probably crack a side seal or apex seal before you crack the housing.
Just tune carefully.

On the side note, 3mm apex seals give you more margin for error when tuning (whether it's fuel related or seal material related). Some people are willing to pay for it.
Also, 3mm is a way to use a used rotor or a rotor with an apex seal groove that is beyond spec.

J

Badog

Good information to have. Getting ready to have a new block built and I'll think I'll do it with the new rotors then. Yes, I'm going with 2mm, rather than the 3mm. I know I can tune the car. Off the check the Racing Beat rotary guide....Thanks Es!

Tony

Northwest FD3S

Thanks for all of the helpful info. this will help alot in decisions down the road.