Reese04

Has anyone tried to install a newer Ford Mustang Coyote engine? I need HP without blowing the engine. Local mechanic, tuner, tells me my 1991 Foxbody Mustang 5.0 HO will not go far above 500 HP at the crank. Says the block will break or the crank. Just not built heavy enough. I want at least 500rwhp.

mrmustang

500HP in a V8 Miata (or a Cobra replica for that matter) will not be streetable. I had a 347 stroker with a Vortec T trim supercharger in an early FFR back in 2002 and the car made almost 600hp at the rear wheels, completely not comfortable on the street, but a great 1/4 mile car when traction could be found. I suggest a step back, and a deep rethink in regards to your lofty HP aspirations. 350-400 is about the limit for the street in these cars, and you better include chassis and suspension updates, along with at least a Harddog double diagonal rollbar.

Bill

Reese04

Thanks Bill. Did you used to be on the old Monster Miata Forum years ago? I was on there allot when I was doing my build in 2004/5. I got allot of good advice and info from those guys. That was before the LS1 mod kits were made available. So talking to the local Mustang tuner/mechanic there is not allot I can really do to increase horsepower to any appreciable amount with supercharging or turbocharging. He said turbocharging requires allot of welding and the Miata just does not have the space. What other mods are out there that I can drop in and increase power that is worth the boost for the buck? And yes, I have the BossFrog double hoop rollbar that is one solid piece that mounts to the frame in 6 places. They used to have a video of a rollover test with it. Amazing!! Dave

mrmustang

Here, there, and everywhere in between, Cobra replicas for me, V8 (all Ford related) Miatas (11 to date) for my wife.

A simple, well built, 5.0L with a set of aftermarket aluminum heads, and a fuel injection setup of your choice is good for an easily streetable 350-400hp. Again, no turbo, no supercharger, no ultra high compression or radicalization of any kind needed. Stop getting caught up in the higher HP hype/bull, it's nonsense unless you are planning to strictly track to the car and not drive it on the street at all. History, and vast experience with multiple track and street cars tells us that you can only put so much usable HP on the pavement. Your limitations are the drivetrain, suspension, and tires you choose. The Boss Frog is similar to the Harddog, so you are good to go from there. Don't over think it, keep it simple, simple is reliable, and reliable is simple. Stock 225hp, 5.0L Mustang motor from 1993 in a miata is enough for high 12's to low 13's in the 1/4 mile.1991 Mustang gt weighs in at 3190lbs
1991 Miata weighs in at 2182lbs

Mustang engine in stock form puts out 225hp/300ft/lbs of torque

Miata engine in stock form puts out 116hp/100ft/lbs of torque

Adding the 5.0 engine, transmission, IRS rear end to the miata only adds 170lbs to the entire car
New Vette: 53% front and 47% rear
New Camaro 52/48
New Mustang 54% – 46%
Stock Miata (2014) 52/48
Flying Miata V8 (with aluminum heads) 52.3F / 47.7R
Monster Miata (cast heads like this car) 53F / 47R

Reese04

What are your thoughts on installing a Nos kit, say about an additional 100 HP? I'm thinking of putting the bottle in the trunk. Mostly for show. My fear is what happens if Nos is applied when I go to shift gears and put in the clutch....Boom!!!??? All load will be removed from the engine and the Nos may over rev the engine blowing it. I don't know. Anyone have any experience with Nos in an old Foxbody 5.0??

mrmustang

I have had NOS only in Mustangs and one early FFR Cobra replica, for show, an empty bottle is all you need, for the real thing, only if you plan to drag race, useless for all other purposes, show or otherwise.

Reese04

I found a guide on line concerning swapping the Mustang 5.0L/302 engine with a 351W engine. The biggest change that I saw was the height change of about 1.5", plus the block is wider, which I have heard is not a problem. The 302 has a deck height of 8.2" where the 351W is 9.5" a difference of 1.3". Right now my 5.0 has several spacers on the engine mounts so that the oil pan clears the Miata K member. With some further K member mods, those spacers could be pulled out. I have heard that you can also add spacers between the K member and body thus lifting the body up off of the engine. Other advantages to this swap, the 351 uses the same computer as the 5.0/302, can use the same heads, not sure about the header pipes, I believe the alternator will also work from the 5.0. The 351W by itself stock, runs about 350HP. With added mods to cam, intake, fuel injection, MAF, throttle body could boost it up to about 500HP. Yep, without supercharging!!! They also briefly speak about a modified 351W engine from Ford Performance that is a Boss 427. Just imagine that under your Miata hood. I have seen a few of those engines in the little two seat Shelby Cobras. Here is the link to the guide.

https://lmr.com/products/Mustang-351...SAAEgJAw_D_BwE

Let me know your thoughts please. I don't like going all the way backwards with a different engine. But this seems a bit more practical than a Coyote or something else.

engineer

Hi Rees04,

I concur with Bill. You will not be able to use 500 rwhp very well.

351W is possible in a Miata but will need more mods to get it to fit (hood, headers, steering rack etc)

My advice is to spare yourself the headache and cost of going down this road and do the following:

Use the 302W engine in a stroker format and an aftermarket block and make anywhere from 400-550hp at the flywheel, depending on spec (331/347/363). A good 331 will make you 400-450 hp, 347 425-475hp and the 363 will get you 475-525hp all in streetable form. More power is available but the engine will likely be too heavily cammed to be fun. This 450-500hp will be enough power for the Miata AND make it enjoyable to drive, adding more power just gets wasted as it cannot be put down without wheelspin.

Also a 500 hp target will ensure that the diff, gearbox and axles all live for a long time.

I set my target at 450hp for my 331...it hooks up, is decent on gas, idles all day in traffic and is 100% reliable.

Many cars have been spoiled by owners being overly ambitious with their goals..especially around power.

I know its tempting..trust me I know.. you think that if 400hp is good, then 500 is better and 600hp is better still..... But reality dictates a different path as there is a "goldilocks zone" in any car where the abilities of the engine, drivetrain, chassis and suspension all work nicely together.

For me that goldilocks zone power limit in the Miata is somewhere between 450-500hp at the engine. Go higher and the car can "unravel" from a balance perspective.

Also a 427 in a small car needs careful engineering..Carrol Shelby always said the best engine for the AC cobra was the 289 as it had the blend of revs, power and weight distribution to make the car fun to drive.

For the Miata (being a much better chassis than an old AC Coibra) I would say that its a 331 (with stock block) or a big bore 347 on an aftermarket block tuned for 450-500hp...Just perfect

Reese04

That sounds perfect. But what year range of 302W am I looking for? I was told that the 302 in the old foxbody Mustangs were weak blocks and could not take the horsepower. I have a 1991. I assumed that the newer blocks would not fit with the current engine mount in the Miata and would require all new bolt ons. Help!!

Just found the Ford Performance Boss 302 blocks stroked for 347 or 363 cu in. made to replace the old Foxbody Mustang 5.0 like mine. If I can generate around 500 hp w/o a supercharger, then I'm going that way!! Any concerns with the 363 stroker that you guys know of? I'm gonna run what engine parts I have passed Ford first to see if I can get an answer from them since it looks like all of my current engine parts will work on the Boss block.

Reese04

I have decided to go with Ford Performance Boss 302 Short Block, Stroked 363 cu in. I have a 1991 Mustang 5.0L Foxbody engine, and this new Boss will go right in. EVERYTHING on my current engine will just bolt right up to the new Boss, including the cam and heads, intake and exhaust manifolds. No issues with valve clearances either!! I wrote Ford Performance, sent them spec sheets on my cam, heads, lifters, pushrods and got their blessing. I'm good to go, once they are back in stock. They are sold out for now, but they are going to be manufactured again later this year. I will need a new harmonic balancer, head gaskets, and a few other parts, but it's fantastic I'm not stuck with a block that will blow once it goes over 500hp. I won't need to supercharge it either.. It will look exactly like it does now. Has the same 8.2 deck height. No one will be able to see any difference. Just more hp and performance. Yes, I do plan on installing 90mm throttle body, MAF, and 42lb injectors, and a new dynotune. It should push around 400 rwhp, I'm hoping.

https://performanceparts.ford.com/part/M-6009-363