90 5.0 Lacking Topend Power, what to do?
 

After playing with my 5.0 Miata for a couple of days, it seems very soft on the top end, it revs up there, but not too much go. It has headers & Explorer intake, it is still running cats. The engine seems to run correctly, just not very powerful.

Is this typical of this engine?

What are the major bottlenecks?

Will losing the cats help a lot?

Do I need aftermarket heads & a cam?

Thanks.....by the way, I'm kinda digging this thing! Thanks, Tim

How is your fuel pump and gas filter? Does your engine need more gas than it is getting?

It doesn't feel like it's short on fuel or a bad fuel pump, not studdering.

Get it dyno-tuned by somebody that knows what they are doing. This will show you exactly what you have & what is going on. No guessing.

Tim I'm going to answer your questions with questions. We need to know the set up to know if what you have is typical. Is the engine stock 225 hp Mustang / Explorer? What headers and mufflers are you using? Any tune work or performance mods done to the car at all?

Breathing is the bottle neck both in and out but usually removing the cats will change it very little.

Do you need aftermarket heads and cam? For what? What are you going to do with the car and what power are you wanting to achieve?

What experience do you have with the car? Like did it have more power last summer but now seems wimpy. Have you timed it in a 1/4 mile to see what it does either at a track or just on a back road?

My hunch is you have nothing at all wrong with the car if you are a stock explorer set up. They are fast but not fire breathing dragons in stock form and Tbone is spot on you have no way of knowing with out a good dyno tune. But cover the basics first and make sure what you have is running right. If it is and you want more just remember you can have tons of power, reliability or low price - pick any 2.

Thanks guys! The car is new to me as of Thursday. I was told it was a 90 HO. It has the MM headers & the Explorer intake. The rearend is the 3.27. The trans is suppose to be a 94 T-5. The oil pressure is pretty high according to the dash. That is about what I know.

I am use to 3500 lbs @ 400+ RWHP with 4.10 gears. I think I would like to get to about 300RWHP with this with proper gearing. I will throw it on a dyno & let you guys know. I bought this car more out of curiosity, I wanted to see what could be done with a light car that handled.

I guess part of my question was.....is this what a stock 90 5.0 runs like? I hear the cam is pretty good but the heads are extremely restrictive. Is this a fair assessment?

What does a stock 5.0 with headers put out a the wheels?

Thanks, Again!

Hang on for Jason to chime in here because he is the man for this question. If it is stock (and it sounds like it is) you would be at around 225 HP at the crank. So that 3500 lb 400 rwhp car may be able to beat the Miata but only till the first corner... :D

Depending on if it is running well, you can start by looking at a good cam and GT40p heads, probably going to be the cheapest/best first step, depending on how good the intake manifold is right now. I'd be poking around a Fox site, or a few other ford mustang modding sites.

Thank you, I am going to bypass the Gt40 heads & just proceed to aftermarket heads.

stock injectors? what size TB?

Good move!

When I swapped out the 24# injectors for a set of 42# injectors with a custom tune, the power increase was incredible.

At what point did you change them out? IE, was it after the heads...before???? I see you have a blower!

Stock horse power at the crank for a Mustang 5.0 was 225 and only 205/215 for an Explorer motor. While that sounds pretty bad they can be very easily "woken up" with a few bolt on parts.

If it's a stock Mustang HO engine the bottle necks are (in order of badness):

1. mass air meter/throttle body/EGR spacer - increasing the diameter of all of these together will help.

2. Upper/lower intake - it sounds like this has been taken care of for you already. The GT40 Explorer parts are fine they are just being held back by area 1 and the next one:

3. Heads - the stock heads are known as E7 heads. They are bad. Remove them.

The stock Mustang cam is actually not that bad, especially if you replace the stock 1.6 rockers with 1.72's. If you have an Explorer cam you need to get it out of there.

The nicest combo I had for street/track/mpg's was the following:

-stock 306 block, flat top pistons, stock crank
-1992 Mustang cam
-GT40 (not p) Explorer heads with upgraded valve springs (very important) and light porting.
-GT40 Explorer intake, throttle and mass air meter
-Explorer 19 pound injectors
-stock 1991 Mustang a9l, no aftermarket tuning

The above combo got me 240 RWHP (about 300 at the crank assuming a 20% drive line loss) and 25+ mpg. Essentially I built a 1993 Cobra 5.0 with a better cam and valve springs.

My current engine is closing in closer to the 400 crank magic number. However, it's not built from the 90's Ford parts bin like the above one was.

Hope that helps,
-Jason

Thank you very much....now we're getting somewhere! I'll dig in & see what I have.

The 24# were installed with the Trick Flow heads & used with & without forced induction. The 42# were added later with the addition of a MSD box & 80mm (up from 72mm) MAF.

Buying used parts is always a nice power/dollar trade off, IMO. For me, I got a $600 CAI for a vette for $200, which is a nice deal. Saw this in our own FS/Trade section, and I think it's right up your alley.


https://www.v8miata.net/v8-miata-rel...njectors-1611/

Hi, Thanks for the "heads up"! I PM'd him.

The 302 HO is known to have great low end torque but top end in stock form ain't all that great. My car has the non-p GT40 Explorer heads and intake, true dual exhaust with cats, and open air filter. That's it. It's quick but not fast and still fun. I say it's a mid to high 13 second car the way it is.