v8miata

Howdy,

I posted previously about my alternator problem, figured I would post a hello thread and some pictures of the car.

1994 Mazda Miata with a 1993 5.0L motor swap.

The motor is not stock, I don't know what cam has been put into it or what other non-stock things have been done to it. It has a Tremec T5 5 speed and ford 7.5" rear end. I believe the intake and throttle body are not stock.

Wilwood front brakes, stock rear disc brakes, koni adjustable suspension, custom exhaust clear back to make it fit into the miata body. 195/50 R15 are the tire sizes I believe.

Below are some notes I've made regarding the car (I'd love to hear some input on any of the points below):

1) The motor is smooth up to 4k rpms... from 4k up to 5.5k (I don't really push it beyond that) under LIGHT throttle the motor has a good amount of vibration/shuddering. Of course under full throttle you whip through the rpms so fast you don't really notice it. Not sure if it is the nature of that motor or if something might be wrong?

2) Only in 5th gear at 70-77 mph (around 2800-3000 rpms) there is this very light rhythmic vibration that you can audibly hear and feel through the throttle pedal. I can't replicate it at any other speeds/gears. (I have changed the transmission fluid, it looked good before and was full)

3) The car is losing about 1 qt of oil every 1000 miles (no visible leaks). I am kind of bummed about this one, but I own Subaru's so I am used to topping off engine oil.

4) I just got back from the local dyno shop, they just did a quick hp vs speed test. The car came in at 212.1 rwhp. With an estimated 243 engine horsepower.

Between this and the oil consumption, does this 212 rwhp seem correct? During the test, I did see one small puff of smoke come out of the tail pipes, not sure if that was under acceleration or deceleration though. From my understanding, if the former then some rings are bad, if the latter, then valve guides are bad on this motor. I haven't done a compression test yet, I was hoping to get some feedback before I start any investigating.

jwog666

power seems about right for a 302 of that era, i would suggest performing a compression test to see if any cylinders are low. the smoke and consumption is most likely caused by hardened and leaking valve seals( easy fix)

jsimmonstx

The vibration at speed may be caused by the pinion angle.

jwog666

or the type of enigne and trans mounts used now that i think of it, if solid pieces were used, it wont dampen any vibration

88 orangepeel notch

The intake, throttle body, and MAF sensor look stock, but the intake is polished up nice though. The headers are not stock and as for the cam, I'd only be guessing. Power seems about right for a stock 5.0.

Oil usage I'd agree with jwog, valve seals are bad. I just replaced mine last year as I was going thru a quart every 6 - 700 miles. My wife and I did the Hot Rod Power last year and put on 1900 miles and only used half a quart. And no more embarrassing smoke.

Vibration could be alot of things, wheel out of balance, u-joints, bad pinion bearing, etc, etc.

Gotta say though, that looks like it'd be a very fun car, congrats, looks very nice.

v8miata

Thanks all, you have been great. I have lots to learn about this motor. Watched a youtube rebuild series, seems straight forward, I was actually expecting more complication. Used to 4 cylinders with DOHC...no pushrods, etc.

So it looks like it is a stock motor. The guy who built it made me think otherwise...or it is modified (cam only) and just putting out some poor power. I guess a compression test is next.

Never even knew pinion angle could be an issue. The angle is slight if any but good to know about.

And I haven't looked at the motor and tranny mounts to see if they have rubber bushings or not for the vibration. It is on my to-do list now!

The valve seals look doable also, another youtube video was showing that you can do it without removing the heads but I guess you need to use some compressed air in the cylinder to keep the valve from falling down once detached from spring. Might give that a shot.


So my next questions... what can I do to this motor (if it is indeed stock and compression is fine, etc) to get some more HP and stay smog legal in California? I guess a search on the forums for CA 1993 owners is next.

I am also going to get the car weighed to see what the hp:weight ratio is. I think the car might be in the 2100-2300lbs range. Hopefully not 2300. 10lbs:1hp is my initial goal but want to improve it.

This motor appears to be possible to get to 400 crank hp pretty easily (not sure about staying CA smog legal though) and if I can get the car lightened up to 2100lbs...that is 6lbs:1hp.

There is someone on the miata forums that has a turbo'd 4 cylinder miata down to 1800lbs I think...so it is in the realm of possibility. But I don't want to tear up the car in the process either, want it to look mostly normal.

Thanks again all!

64bit

V8 miata

I'm going to bring it up, because it matters.

That is not a 94 engine. Like we told you before.

It's a 93 or older.

88 orangepeel notch

Yes, valve seals can be replaced with out pulling the heads. Easy, but time consuming. Patience is key with this job.

If you don't have compressed air to hold the valve up, you could use the rope trick. But I didn't want to introduce foreign material into my cylinders that the rope might pick up on the way in.

As for the power mods, the world's wide open. Only limitation is the bank account. I'd is the "search" and dig up older threads and research what you want. It's all been done before.

Good luck

v8miata

Yes, Still trying to build the story behind that.


The smog sticker registered to the car says a 1994 Ford 5.0L. You all are saying it is a 1993 motor. I will trust your judgment.


My inquiries on the matter has led to the following story:


1994 was a crossover year for ford. They did issue some 1994 model year mustangs with the 1993 engine in it, because of this, the smog referee in CA allowed for the 93 motor to be placed into a 94 model year Miata. There is a strict rule with motor swaps in CA... you CAN change motors, but the new motor must be the same model year or newer than the car you are placing it in (and the motor must have all factory original smog equipment).


So yes, I know it is a 93, but I will probably keep slipping and saying a 94 because that is what the smog sticker on the door says.

64bit

Sadly this is 100% false.

The ONLY reason that engine managed to get into that car, is quite literally because someone screwed up.

The wiring you have is from a 93 and older. The components you have are 93 and older.

Which is actually funny, because a true 94 engine would have fit easier.