John,

I don't know how much gain using the stock efi intake. Years ago we dynoed the Arizona Speed manifold against a single plane modified for injectors. The single plane made 80hp more so I don't do much work with the stock manifold.

I prefer the Dart heads because the short turn radius in the exhaust port is better for marine engines. I can machine the port to peak at .650 lift @ 300 cfm. Most other heads don't have the material in the port floor. They flow great at .800 lift but have a hole at lower lifts.

Wedges are inserts that are single bolted and epoxied in the floor of the intake ports. They will add dyno proven 35 hp gain plus whatever port work has been done. They increase velocity in the port by reducing the area in the port without any airflow loss in the usable camshaft lift range. Airflow losses are at .700 lift and higher. This allows you to use a larger intake valve to increase airflow. The work the best in small cubic inch motors although we have used them in 540 cid. Also for the skeptics I have them in our 510 race motor.

I have a set of them in my 468 , seat of the pants - They work period.

Jim,
Have you done anything with the BB Dart Iron heads?
Sprague
213 575 2367

JIm,

Maybe this is why the new 525 EFI from Mercury only makes 540+- horsepower on the dyno. How close is your cam to theirs? What do you sell, parts or complete motors? Have any of your customers dropped the EFI in favor of intakes and carbs? What do you recommend here?

Thanks, John B

Hey Sprague, how you been?

Dart claims the Iron and aluminum castings are the same. Iv'e been doing a ton of the aluminum castings. I have a couple sets of iron comming up, I could let you know the results.


John B

Our 540 cam is considerably bigger than the merc primarily because the heads will support it at higher lifts. We use hydraulic rollers for durabilty and lack of maintance. Our base cam lift is just under .650 lift. but may change according to boat weight and hull design. The heads are ported to achive max flow at the same number as max lift.

I believe an after market programable EFI tunnel ram set up is superior but pricey.

I have a pair of JimV's fully ported Dart Pro-1's 310cc heads on my naturally aspirated 9.6 comp ratio 540's. On Tom Earhart's dyno they made:

682hp/651tq @5500rpm

699hp/639tq @5750rpm

Peak torque was at 4800rpm---704 ft. Pounds.
The boat is a 32' A/T and I have it proped out with 32" Bravo Ones and turns 5600rpm @WOT.

Not too shaby for N/A 540's with hydraulic roller cams

Thread from a long time ago....