Blue Thunder MR 4V intake plenum divider mods?

[wsu0702]

So I bought this used BT 427MR 4V intake a few weeks ago.  I almost did not buy it because the plenum divider has already been cut down quite bit but the price was soo good I took it.  So the plenum divider is cut down by ~1-3/8".  I will not be running a carb spacer since my application is a shaker equipped mustang. Is the divider cut down too far?

[fekbmax]

What type carb are you running ? Dp or Vc ?
I'd run it, try it like it is. It's deff fixable though if need be.

[cammerfe]

Many years ago, I was involved with one of the original dozen CJ mustangs. There was a lot of hand-work evident in the car as we got it, delivered to Romy Hammes,in South Bend. We drove it home to Detroit and went to work.

One of the parts that came to us, along with a visit from Al Buckmaster, was one of the earliest Side-Winder manifolds. It was probably made in the little foundry at The Rouge since it had no markings at all except the firing order. It had Medium-Riser runner openings and had been welded to add enough material so it would seal at the bottoms of the runners. But most important for your situation was that the completely open plenum had had a fore-aft divider welded in. We were told that the divider was necessary because we had one of the Mustangs with a C6 transmission. The manifold was originally designed for the characteristics of a stick-shift.

KS

[wsu0702]

What type carb are you running ? Dp or Vc ?
I'd run it, try it like it is. It's deff fixable though if need be.

Dp.  I read Jay's BT plenum divider testing results and in that he got the best results with a 1" cut on the divider and a 1/2" carb spacer.  I won't be running a 1/2" spacer but the plenum is cut down about 3/8" deeper.

Thanks.

[Joe-JDC]

With generous ports of the BT in volumn, it will lose torque with that divider cut down.  I have dyno tested several different spacers and manifolds with the divider cut and with it solid.  Almost to a manifold they all liked the divider in place without a slot.  I know most folks here think the slot is cool, but it is not what I have witnessed on dyno testing.  BT makes manifolds for other engines also, and they definitely respond best with the divider not slotted.  If torque is not an issue, then consider fuel distribution.  The wall helps with fuel splash spill over.  Keeping the planes as even in flow as possible is a plus for the street, not so much for a race engine.  Joe-JDC

[Drew Pojedinec]

Joe,
I know the intakes are different, but my BT MR 2x4 intake is four hole for each carb.
What have been your experiences on using a 4 hole vs an open spacer on this intake?  same result?

Thanks,
Drew

[My427stang]

To the original poster, what is the engine it is going on, the more specific the better.

With big inch FEs, IMHO, you gain more than you lose when you get a decent sized plenum for the long and relatively small runners (compared to other big block  V-8s), however, the smaller the engine, the more you will lose down low and may never really pull hard on the port to make it up

[Joe-JDC]

Joe,
I know the intakes are different, but my BT MR 2x4 intake is four hole for each carb.
What have been your experiences on using a 4 hole vs an open spacer on this intake?  same result?

Thanks,
Drew

That BT MR 2x4 intake works better/flows better with a four hole with the center blended under the open tract between the two sides.  The blending is simply used to keep turbulence at a minimum.  If you don't understand what I am saying, pm me and I will try to send pictures by e-mail of what I mean.  I can take pictures tomorrow.  Joe-JDC

[Drew Pojedinec]

I understand completely.

thank you sir,
Dp

[jayb]

Some information on one engine I tested with the BT intake and different plenum divider and spacer combinations is at the link below:

http://www.fepower.net/Dyno%20Results/dyno_results_6.html

[wsu0702]

To the original poster, what is the engine it is going on, the more specific the better.

With big inch FEs, IMHO, you gain more than you lose when you get a decent sized plenum for the long and relatively small runners (compared to other big block  V-8s), however, the smaller the engine, the more you will lose down low and may never really pull hard on the port to make it up

Still in the planning stages but it will be a 480+ CI FE based on a 427 block in a '69 mustang.  I would like to keep it street friendly in that I would like to drive it work occasionally and maybe even a long trip so not looking for full race only setup.  It will have a gear vendors overdrive.

[NIsaacs]

I have never had a divider cut on a dual plane manifold, but every time I use a 1" spacer on one I get hard starts and cold blooded off idle stumble. With the engine at operating temp they seem to be fine but still start hard.

I would think that with dyno testing under controlled conditions and looking for performance gains you might not notice the little drivability issues one can encounter in a vehicle.

Nick

[Barry_R]

Try it.
No other way to know.
Having run about a thousand dyno tests on these things by now I can come to realize that spacers are simply something that must be tried.  I have had wide open plenums make great torque, I have had four hole spacers make bigger power upstairs.  Damn motor cannot read the magazines....

[Rory428]

Gotta agree with Barry, the only way to know for sure is to try it. On my Fairmonts 428s and 427/454, the car has gone quickest and fastest, using a dual plane Ford Sidewinder, with the divder cut down almost all the way to the upper floor. Years ago, my buddy milled the divider down, and about 3/4 of the length, then he fabbed up 2 small divider sections, that snapped into place, that would allow me to either add 1 section, to bring the divider wall up 1/2 way to stock, or with both in place, make the divider back up to full height again. I tried it all 3 ways, and with the divider totally gonenetted the best 1/4 mile numbers. Keep in mind, my Fairmont is not street driven, and has a 4 speed Jerico, so when on the track, it sees no part throttle, low RPM use, so what works on my car can be very different than what a mild street engine experiances or wants.

[wsu0702]

To the original poster, what is the engine it is going on, the more specific the better.

With big inch FEs, IMHO, you gain more than you lose when you get a decent sized plenum for the long and relatively small runners (compared to other big block  V-8s), however, the smaller the engine, the more you will lose down low and may never really pull hard on the port to make it up

Ross yes my current plan is for a big CI build.  483CI.  1-3/8" of the plenum divider cut down and no carb spacer. Mostly street occasional strip application.