This is a terrible idea. I love it!

When you say cast iron exhaust do you mean you're planning to use the stock manifold? Dutra Duals are still pretty compact and would make achieving your power goals much easier.

Whatever direction you go with the clutch, keep in mind that a slant at that power level will be making almost double the torque of the rotary.

Probably not that relevant to your plans, but here's the thread on that RX7 build.

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

Standard cast iron at first. I am mounting the alternator and AC compressor on the driver's side. Not sure about clearance yet. Clearing the starter with the Dutra Duals won't be a problem since I am using the Mazda starter mounted backwards on tge transmission.

I am aware of the torque difference. The rotary has about 160# of torque. The clutch in the rotary is about 1/8" bigger or smaler than the 9 1/4 slant clutch.

My build will be very mild with an empasis on smooth and quiet.

I am not planning on racing and I will be driving the car myself, so I don't think the clutch will be a problem. If a problem arises they make heavier clutches for the rotary.

The car is very light and I think the tires will slip before the clutch slips.

I read the RX7 post. The RX8 seems to gave more room under the hood. They put OH cam straight sixes in them and the hood still shuts.

I appreciate the input. It will be a fun car to show when I get it done.

Buddy of mine used to have an RX-8. He loved the car itself, but had nothing but issues with the rotary motor and Mazda finally bought the car back. Sounds like you have the solution for the problem.

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Official Cookie and Mater Tormentor.

so what became of the truck that donated the engine? or did you get "just" the engine from a junkyard?

It's sitting outside. The truck will drive forward, but no reverse. I'm going to try to get $600 for it with no motor or trans. I had done a lot of lurking on this site, plus watching Uncle Tony, and I knew a late model slant had the lightest block and crank. I'm not building for power, but if I can get 6,000 rpm the HP should be there.

The motor in my Valiant is a light crank with stock rods and pistons. I shift it at 6300, and it occasionally goes 7000 in the water. RPM won't be a problem but if the head hasn't been done well making power will.

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Official Cookie and Mater Tormentor.

Slantzilla, from what I have read, that is pretty good RPM. So they don't explode at 7,000. That is good to hear. I'm building a long rod (Molner 7.005 narrowed for the cast crank) with 2.2 turbo pistons cut down to give me a zero deck. From what I have seen there will need to be valve clearance and a dish to keep the compression reasonable. And I am trying to achieve "squish". May have to weld the head a bit plus a shave.

My research tells me that longer and lighter rods, and lighter pistons should give me a little more rpm's. I know the head will need serious $$$$ work to make it breathe at the higher rpm's. I'm having a custom efi intake built.

The Mazda is light (3,000#) has a small frontal area. Maybe that wil help.

I've watched and read a lot about the early racing days of the 170. It seems that Chrysler had performance in mind with the alumunum block and long runner intake. Then I guess the practicalities of making a profit changed things a bit.

So, again, my goal is to modernize the slant. Quiet, smooth, reliable, and free revving.

Thanks for the help.

Pretty sure some do!
That really doesn't go hand in hand with 7000 rpm's.


There is really no need to turn the long stroke slant 6 much over 6000 rpm unless you have some fully built race motor. The truth is my race motor ran faster at 6200 rpm than it did turning 6500. Mike Jeffrey told me peak HP was at about 6000-6100 rpm.

And while Dennis has hit 7000 rpm that does not mean he is recommending that you do it all the time. Maybe in a 170, but not a 225.

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

I always laugh at people wanting a 170 to turn rpm. That's fun and all, but they make no power.

The bottom end isn't an issue. The head really doesn't flow well enough to make any power above 6500ish.

I used to shift my long rod motor at 6750 on the sauce, but it was done at 6500 on muscle only.

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Official Cookie and Mater Tormentor.