formula31

The purpose was to get HP peak around 5000 rpm. Idles and starts better than stock or efi, which is no small feat with a holley carb. I looked at a lot of cam timing on a lot of engines (older merc hp) (#1 intake cl around 106 if I remember right, Ill check) and read a lot of books and tried all three (+4, 0,-4). Adding 4 brings gets the intake valve pretty close to the piston (.080) but that value is livable as long as you dont spin it too high. I dont pretend to understand exactly what is going on in there and why the +4 works better but it seems give me more power at 5000 rpm. In theory, advancing the cam brings the hp peak in at lower rpm and visa versa. I did this playing with a single engine boat and adjusting the cam timing with a cloyes hex adjust and a timing cover with an access plate. Im convinced but it may depend alot on all the other engine parts and how many rpms you want to spin it. It would be interesting to see if Dennis Moore chims in and what his opinion is. I got some of this information from Alex Walordy, another HP guy and other old time engine builders from the early Hydroplane days.

formula31

Also Bill Fisher and Bob Waar.

blue thunder

Formula.. isn't warlordy the author of the bbc performance marine book you said was good? Where can I find that?

BT

formula31

Not marine though, just old chevy hi performance ideas. I think Summit may have them. "Chevy High Performance Engine Assembly Guide" Alex Walordy. and a better one is "How to Hotrod Big-Block Chevys" by Bill Fisher and Bob Waar. keep in mind this is old tech and has to be tempered for marine use but there is some good info there. Dennis Moores book is better because it is based on marine use.

Waterfoul

You can mill the block and the heads to get just a little more compression too. Not too much or you will throw off the intake alignment.

I also have done some things to my 330. It's .060" over stock, has slightly domed hypereutectic pistons...Merc. magnum dual plane intake.....cam, some mild head work to the Merc. magnum rect. port heads.....and EMI exhaust. From one summer to the next, I gained nearly 6 mph in my 1987 Baja 240 Sport. Not an easy feat by any means. Heavy boat.

dyno and I have similar motors, he has a slightly hotter cam than I do and better heads.....but both motors run really well. You can email Crazyhorse for part numbers if you want. He was a big help to both of us (and several others here on OSO).

Mike

OPIE272

my .02
I run twin 454 330's and have Edelbrock 750 cfm marine carbs, RPM performer airgap manifolds with IMCO thumper exhaust.
I run 48-4900 RPM with air temps of 50 f or 100 f. It makes no difference thats all the RPM I can pull. Our thinking was that the oval "peanut" heads will only flow so much air and that is my weakest link in my system, for now.
I was told to get anymore RPM's from a stock setup and not changing cams, I will have to go to rect. port heads.
To port and polish a set of ovals isn't worth it. The rect. will flow more. The cost to "flow" a set of ovals, you could buy a set of CNC rect. port heads and not have to upgrade again.
Also this is on a Formula 272SR-1 so it's heavy

Brad Perry

One of the first things I would do is lose the flat tappets and go with a hydraulic roller. 30+ hp by that alone. The larger ovals will run just fine up to high 5000s. You might try fooling around with desktop dyno a little and see the difference in the torque curves of single plane vs dual on these combos. Good for ~40-50hp on top with not much diff in between. I've ran a crane 226/236-587/610-112 in that motor with Edel oval heads and a dual plane with great success. Would go with a Single plane and a Holly or Demon if do over..

formula31

Yea, there is a huge difference between the peanut port oval heads and the old large port oval heads that are arguably better than the rectangular ports for most marine engines.

Budman

'Bago Baja,

What kind of speeds are you getting with your 7.4 in your Force? I have basically the same boat - 88 Force 235, but mine started out with a 350 mag/Alpha. With that combination it would run 48 - 52, depending on conditions and how loaded down it is. Since that time I have swapped in a warmed over 454/Bravo. I now run around 60, but I expected more. Mods to the engine include large oval heads with 2.19 intake valves, Comp Cams Xtreme Marine XM270H (226/236 @ .050, .544/.547, 122 LSA), TRW forged pistons with a small dome, edelbrock Performer RPM, full roller rockers, etc. Heads had some minor valve pocket work done on them. I'm running the stock Q-jet with larger primary and secondary jets & rods. Stock Merc Silent Choice exhaust. Pretty similar to what has been mentioned here. I think the Q-jet might be holding me back some - would like to try a Holley this year. I honestly expectted about 5 more MPH out of this combo, as my friend's 89 Force 235 used to run 58-59 with a well worn 7.4. I'm also suspicious that the 1.36 gears in my Bravo might be holding me back - if you search through the threads you will see some discussions of the 1.5 vs. 1.36 ratio in the Bravos.

Interested to hear about your combo and what you end up with.

blue thunder

Budman.. that is the same cam I am considering seriously. Do you like it? How does it idle. How does it sound? Would you use it again?

BT