jr

Like Cord says recalc your CR. I seem to remember that Vortec heads are 64 CC chambers. I'm running 76 CC chambers on my SBC's with World Products Torquer II heads. I had to go that route because my compression is over 10:1. But I agree with Tom, I think your heads are your limitation.

I did some reverse calculations using the numbers you gave, and BAM's speed calculator. All things being equal I think your doing pretty well. There calculator says your running 375 HP. Which was the difference in HP needed to go from 52 to 58. Not too bad.

Did you port match your intake to the heads? I measured the increase in size of the intake port to the heads when I matched mine and I had an increase of 22% on the intake and 17 on the head. That big of a difference will really smooth out the air flow and build power.

TomZ

Actually, you'll be over 10.5:1 with the Vortec heads (combustion chamber volume is advertised at 64cc's but in reality they come out more like 61cc's) so scratch what I said earlier. The WP Sportsman II's (72cc) would probably be a better bet, though the expense would be much more than that of the Vortecs. To use the Vortecs, you would need to change pistons in order to make it exceptable for marine use (unless you like paying for race gas). The Sportsman II;s will probably get you right at about 10:1, and with the fast-burn combustion chamber you should be able to get away with using premium fuel.

I was going to mention something about the prop as well. That cam will allow you to produce a ton of torque down low (torque curve should be flat as a board), but still that's a lot of prop for being behind a small block in a single engine application I think.

Preuni

This board really rocks! Thank you guys for all the info.
first thing I will do is bump up the timing to 36 deg. and see what happens. Next thing is that the heads will have to go, I am sure they are contributing to my problem big time. Anybody selling a pair of ported WP Torquer II heads with 72cc chambers??
That motor should spin my 23 Mirage at least 5K, the boat is light (2900pds) and the hull is built for speed......
Just tried a 21 Mirage today, 4800 rpms 60 mph GPS. Still too slow, considering that the boat has a SternJack...On this board I read apost a while ago that a Pachanga 22 with an 406 ran 72 GPS, so there has to be another 5 miles or so in mine!
!
Thanks again everybody!
Andy

Vinny P

Preuni:

I don't understand why you are being advised to increase ignition timing to gain top end!! This theory is wrong. The more timing is advanced the less top end power you have. That is why M.S.D. sells a timing retard system. I have used it in my drag racing days to retard the timing when pulling gears to gain top end. While 32 * advance is not alot, I don't see how going to 36 * will help you much, if any at all. I think that your problem lies in those cylinder heads. What size valves do you have in them? I have a set of 2.02 intake, 1.60 exhaust 292 casting #, angle plug turbo heads that are mildly ported ( just deburred ), 3 angle valve job, but they have 62 cc chambers. I am looking to sell them. I don't think I will ever use them for myself. If interested let me know.

TomZ

Retarding the timing takes away power and makes the engine respond like a dog (think back to the old days when the octane dropped and the timing had to be knocked back in order to keep those old muscle car engines running). I think he's down on power all across the board and bumping the timing up a couple of notches would help the engine build power.

It works on our Fuel dragster...

ForrestC

KAAMA, I need to talk to this guy who's running 78 MPH in his Magnum 27 with a pair of 383s. That's impressive!

KAAMA

ForrestC,

Well, if I remember correctly that is what I was told. I don't know the dude who owns the boat neither do I know what mods have been done to the engines/boat, but you're more than welcome to call Wolff and perhaps he can give you the owners number, but Wolff is the one who built the engines. 616-422-1090

BTW, I don't know much about the 27' Magnums and/or small blocks either, therefore I don't really know if that speed (78mph) is really a stretch or not----it certainly sounds fast. I just know that those 27' Magnums are very cool looking older boats. I always see one in St. Joseph with small blocks and tail pipes coming out from the deck some how and over the transom. Some older dude owns it and when I see him at the lauch he walks around that boat prouder than a peacock!

candyman35

ForrestC,
I think the boat that Kamma is speaking of is Greg's from Gorilla Powder coating in Crestwood, IL. I'll try to run by his shop and get his phone number for you. His boat was featured on The Lovely Lady's of Motor Sports a few years ago. The whole boat was restored. Here is a pic I took of it a few weeks ago.
Dan

ForrestC

Magnum 27s are great looking and great running rough-water boats, but with their heavy lay-up, they are not at all light in weight. For that reason, you really have to work for MPH on the top end. I'm running a pair of 383s in my 27 Magnun with 200cc intake 64cc Dart Iron Eagle heads (9.2:1 CR), Crane H-272-2 cams, Stainless Marine exhausts, and I'm in the low sixtys MPH at best; however, that's with old 1.61:1 Volvo 280T (with power trim) drives and Hill 27" pitch propellers. I'm sure that the Volvo drives and their limited prop selection is killing the top end, and for that reason, I'll be installing a pair of Hydromotive nose cones and getting some additional work done on the Hill props by Hill Propellers. Some day soon, Bravos, Arnesons, or something will be in the works, but for now I'll be working with these old Volvos.

Thanks again for the contact.

Havasu Hangin

I currently have a Volvo 280 drive (with a Hydromotive nose cone I installed- not fun), and I'm having trouble finding a top plate to attach an external steering ram.

Are you running external steering? How is the tie bar and ram attached to the drive?

BTW, 27" seems like alot of prop. I am also running a Hill turbo 3-blade. What size do you need? I can check around...

I hear ya on the old Volvos...no one has performance parts for my old drive...