Cutting center divider and other questions

[Bolted to Floor]

I've been told I can gain 5-6 HP by grinding down the center divider on the RPM intake about 3/4". Can you get the same results by installing a open spacer?  The intake has not been port matched either.

What's a good choice for a coil using a duraspark distributor and box?

Any ideas if a RPM intake, 1/2" to 1" spacer, and air cleaner will fit under the 67 style Shelby hood?


Using the Wallace racing engines calculator, the static compression is 9.74 to 9.84 depending on deck height of .005 to .0 using the 11.7cc value.


Bore 4.11
Piston Sealed Power 381NP-.060 over - 10.33 to 11.7 cc depending on where I look.
Crank Stroke 3.98
Rod length Stock 6.488
Deck height 0 deck to .005 in the hole according to the Machinist
Cylinder head – Felony heads from Barry 76 cc chamber
Head gasket Fel Pro 1020
Comp hydraulic roller with .574 lift, 227 duration, and 112 lobe separation installed at 106
Timing chain Ford Motorsports with 9 position key way
RPM intake
750 vac secondary set up with rear meter block for 4 corner adjustability



 

[plovett]

I would try whatever height open spacer you can fit under your hood.  I don't know what will fit with your Shelby hood.   I would certainly try that before cutting your manifold as the spacer idea is easily reversible, while the cut down divider is not.

If height is hard to find a drop base air cleaner helps.   I have little hood clearance in my '67 Cougar with a stock hood.  I use an L88 base plate which drops the air filter way down, a 3-1/2" K&N filter, and a 1" spacer.  Also, my hood is raised up slightly at the rear with washers under the hinges.  I still have witness marks on the air cleaner lid and underside of the hood from the engine rocking back and forth.

What I'm getting at is I think it's a good idea to use all your available height for spacers and/or air filters. 

JMO,

paulie

[Joe-JDC]

If that is true, the gain in horsepower would only show up at the very top of the rpm range, and you would most likely lose torque at the rpm you drive at most of the time.  I know there are a couple of folks who race a dual plane that claim their car is quicker with the divider cut, but in all my dyno testing and race experience over the years, that is not true.  It still comes down to the cubic inch, compression ratio, and camshaft used with the head flow to determine if you will actually make more horsepower with that divider cut.  Joe-JDC

[Bolted to Floor]

Paulie and Joe, thanks for the feedback. I figure I could be selling the RPM intake down the road and an uncut center divider would be more preferable to the next owner.

We can see what the dyno says with open and 4 hole spacers. I would be good with a 1/2" to help insulate the carb from the intake. I can worry about hood clearance after that.

[plovett]

Don't forget there's other types of spacers, too.  There's the two hole (open on each side and divided down the middle) tapered four hole, and cloverleaf.  I don't know how much dyno time you'll have, but it's helpful to try jet changes with each spacer type, separately.  Different spacer types can have different optimal jetting.

Please let us know what you find out.

paulie