5.0Rx7

I just got a used 5.0 roller motor that i am going to eventually swap into my 1990 Mazda Rx7.

I have a few questions, as you might have expected.

This motor is a little different than any other stock 5.0 that I've dug into. It came from ford with the x303 cam, as far as I can tell. It has valve reliefs in the pistons from the factory... This might be a common thing that i've just never run into, but I just don't know. What have I got my hands on? The motor is out of a fox body GT convertible. It has never been torn into at all until now...

Also, When all is said and done with the motor build, I'm hoping to be making around 450+ flywheel hp. What 5 speed would hold up behind it, and still not cost me an arm and a leg?

Scout2232

TKO or a G-Force T-5 conversion will handle that. I personally went the G-Force route.

militarymustang88gt

i havent ever heard of a 5.0 coming from the factory with an x-303 that is a frpp cam and someone put it in after they got the car/motor and stock motors come with flattop pistons flycut to an extent but good luck i went the tko route i got mine with around 200 miles on it with a stage three clutch i knew the guy who had it but you can get a t-56 kit now for like 2400 with bellhousing clutch quadrants drivshaft and all

88BlueGT

There is no motor that came in a Mustang with those features. Most likelythe cam, pistons, etc were installed seperatly OR its a FRPP motor. Also, your not going to be able to make 450hp NA on a 302.

5.0Rx7

The guy that i bought the motor from was the car's original owner, and said that everything on it is exactly as it was when he drove it off the dealership. He said that the car was special ordered by somebody else that never came to pick it up after making the down payment, so maybe the motor was part of the special order... I don't know...

But no way to pull 450 with a n/a 302? About what should i expect with cleaned up gt-40 heads, trick flow fuel injection, larger tb, 9.7 compression, the x-cam, and other little stuff and supporting mods? Remember, I am talking flywheel. I don't expect to get 450 to the ground by any means...

5.0Rx7

Just so i don't sound like I have super high expectations, anything over 350 is going to make for a hairy ride. The car is only going to weigh around 2800lbs wet.

militarymustang88gt

if you get the heads decked ported polished larger valves and stuff you might make 350 at the crankbut even after that you will be lookin at around 15%-19% drivetrain loss with a manual trans depending on what rear end driveshaft and all that i would aim more for like 10 or 10.5 comp ratio and you would have a better chance and you would still be able to run 93 n/a if you are ever planning on supercharging/turbo or nos then i would drop it to a max of 9.1

5.0Rx7

Nah, no forced induction in the future on this engine. Maybe the next one...

I was thinking 9.7 just for the reason that i still want to be able to drive this thing on the street somewhat reliably. It won't be my daily by any means, but I don't want to have to pop the hood every time I want to go for a cruise.

Would it still hold up well with the stock crank and rods with 10.0?

militarymustang88gt

my friend has a 306 stock crank h rods 8.9 comp and 14lbs of boost has 480ish at the wheels had 468 with three hundred miles on the motor now that it has 2800 miles on it should have a bit more and tune it a little better but you shouldnt have a prob he drives his from birmingham to auburn twice a month and it is an 2hr trip both ways with no prob the only thing he has a prob with is his msd box gettin wet in the rain

w8less

i had 9.7 in my old 347 just remember to get at least 91octane