Box Intake...Thoughts?

[5.0L Miata]

Hey All,

I have a chance to pick up a custom aluminum box upper intake with a truck lower for my car for a reasonable deal. I know there are a lot of concerns about how box intakes can kill bottom end torque, but was looking for feedback from those experienced with them and a go/no go for using one with my combo.

My engine is:

Stock 91 Short Block
Edelbrock Performer RPM Heads
70mm TB
Stock cam
Running SD, so no MAF

Please also account for the fact that my car weights 2,400lbs and I'm running 3.23 gears in the back.

My reasoning for maybe going with the box intake are:

1) It will save me 10lbs off the front of the car.
2) I can't get the power to the ground anyway from a launch, so I'm thinking with my light car perhaps moving the powerband up a bit is ok.
3) It is a low profile intake so should clear my hood

Thoughts?

 

[millhouse]

Unless you have the valvetrain/cam setup for 6500+rpm shifts (minimum), a box style intake is going to kill your area under the curve. Stick with the likes of a performer or street heat and lay off the twinkies an ho-ho’s.

 

[joel5.0]

If you set it with the correct valve events, you will compensate for the better breathing box intake.

 

[5.0L Miata]

If you set it with the correct valve events, you will compensate for the better breathing box intake.

You mean with a new cam?

 

[joel5.0]

Yep....

 

[5.0L Miata]

Yep....

Not in the cards right now...just put the motor back in the car and don't want to spend the time and effort to pull it again!

How much of a drop/change in power band are we talking here? I know you can't tell me 100% since this is a custom intake...but what kind of a low end torque drop am I looking at?

I'm just thinking my car is about 800lbs lighter than a typical Fox so I don't need the same amount of torque to get me moving. In fact with the stock H.O. 5.0L installed, I had so much torque that I would light up the tires and get axle hop if I tried to launch it with all it had.

Now with the Eddy aluminum heads and if I installed even an Explorer intake...I'm thinking I'll have so much bottom end torque I'll certainly not hook up. This isn't a drag car though, it is a street car that will see the 1/4 mile maybe once a year and the auto-x track a few times.

 

[5spd GT]

Don't band-aid anything.

Buy matched parts.

I would wait for the money to match your combination, along the lines of what millhouse stated.

 

[vristang]

Hey All,

I have a chance to pick up a custom aluminum box upper intake with a truck lower for my car for a reasonable deal.

Depending on what vehicle the lower came from, you may not see any gain at all...???

 

[millhouse]

Not in the cards right now...just put the motor back in the car and don't want to spend the time and effort to pull it again!

How much of a drop/change in power band are we talking here? I know you can't tell me 100% since this is a custom intake...but what kind of a low end torque drop am I looking at?

I'm just thinking my car is about 800lbs lighter than a typical Fox so I don't need the same amount of torque to get me moving. In fact with the stock H.O. 5.0L installed, I had so much torque that I would light up the tires and get axle hop if I tried to launch it with all it had.

Now with the Eddy aluminum heads and if I installed even an Explorer intake...I'm thinking I'll have so much bottom end torque I'll certainly not hook up. This isn't a drag car though, it is a street car that will see the 1/4 mile maybe once a year and the auto-x track a few times.

Your going to need to shift at damn near 7000rpm on a 302 to get into your power band with that type of intake. Unless you have the valvetrain/balance to go along with that type of rpm, it's going to throw your entire h/p and torque curve into an unusable area.

 

[5.0L Miata]

Ok thanks guys, sounds like sticking with a Cobra/GT40 intake would be a better match.

 

[vristang]

Your going to need to shift at damn near 7000rpm on a 302 to get into your power band with that type of intake. Unless you have the valvetrain/balance to go along with that type of rpm, it's going to throw your entire h/p and torque curve into an unusable area.

I'm not sure how you can determine 7k from what we are seeing....
besides... stock cam/lifters aren't goint to 7k are they?

I ran a comp cams box upper on a Cobra lower for a while. The car was basically stock 1990 GT. 2.73 gears.
Because I didn't make any other changes with the intake (camshaft atleast should have been changed), I did realize a loss of low end.

It is important to note the following...
The loss of low end that I experienced was not due to the box intake.
It was due to a mismatch in parts!

If I had changed the gears... the impact would have been less dramatic.

power came on by 3k (big time), and the car rev'd much better after that.
proper gears and cam would have made the car great!


Ultimately the choice is yours...
But I kept my box upper and won't have a problem running it again on another street car...

 

[Darkwriter77]

3.23 gears? Did you mean 3.27's or 3.73's?

 

[millhouse]

I'm not sure how you can determine 7k from what we are seeing....
besides... stock cam/lifters aren't goint to 7k are they?

I ran a comp cams box upper on a Cobra lower for a while. The car was basically stock 1990 GT. 2.73 gears.
Because I didn't make any other changes with the intake (camshaft atleast should have been changed), I did realize a loss of low end.

It is important to note the following...
The loss of low end that I experienced was not due to the box intake.
It was due to a mismatch in parts!

If I had changed the gears... the impact would have been less dramatic.

power came on by 3k (big time), and the car rev'd much better after that.
proper gears and cam would have made the car great!

Ultimately the choice is yours...
But I kept my box upper and won't have a problem running it again on another street car...

It’s simply the nature of the short runner intake on a 302. This of course is assuming your running a cam matched for your combo.

The loss of the low end you experienced was from a combination of the two. The box intake will require a 6500 rpm+ shift point on matched 302 combo. The low end will absolutely suffer…as you are shifting your entire curve up in the rpm range. That’s not to say they won’t make power….you just need to have all of the parts to be able to support that type of rpm.

In the end, if you plan on keeping the rpm’s below 6500 rpm, a box style intake (matched or not) will be detrimental to your combo (including most forced induction setups).

 

[joel5.0]

5.0L Miata,
Since the correct valve events are not an alternative, you definitely need to band-aid the intake side and match it to that limitation. Nothing wrong with that, you need to look at your setup as a combo, not single components. Would a box intake with the correct supporting cast be a better choice?... yep. I know about the "short runner intake = high revs" association usually made, and it is true, when everything else is not "combined" to work together. Have I worked with boxed upper intake setups N/A and FI?... yep, and they will always out accelerate a long runner setup when the supporting cast of the combo is set to work together...... + why are the OEM's using Variable Length Intake Manifolds (VLIM) in everything including trucks? View attachment 310132

It's funny when you read the term "band-aid" when referring to the brain of the whole combo, but if you look at the different setup possibilities, that is what you do when you try to define a combo...... if your constants (in your case camshaft, valve train and heads) are defined, you need to band-aid the limitations those "constants" provide. If you weren't "limited" by not making a camshaft/valve train match up, a box upper (+ supporting cast) would make that short frame light Miata a little dangerous.

 

[strtrcr50]

3.23 gears? Did you mean 3.27's or 3.73's?

He has a miata.

 

[5spd GT]

VLIM is for a nice torque curve down low, and the HP/TQ to take over up top.

Longer runner tuning at lower revolutions, and shorter runner tuning at higher revolutions.

Band-aid can be used interchangeably.

There is a time, place, price, engine, etc. for different style manifolds.

This is not Wal-Greens; the world is not perfect, especially engines.