REALY???
The dyno we use is not accurate? How did you come to that conclusion?

. :food-smiley-007:

Out of the box heads?

Let's keep my education on track.
Thanks

Many marine engine builders have proven 750hp 598ci recipes. And they are NOT 10.7:1 compression. Nor do they have 800 lift cams.

So what dyno do you use? We use a DTS . who's engines are you referring to that dyno happy ?

The AFR 357's are their CNC Head. So, yes probably ok out of the box.

I work in an engine manufacturing facility with 8 certified engine dynos capable of handling a lot more horsepower than anybody on this board is making. With that being said, I can tell you from first hand real world experience that no two dynos are the same. Even from day to day things change.

I see your from Lafayette. Where do you boat around there ?

they were.

Ya buddy, we in it now!

S30, that's a pretty expensive set of heads to only make 740hp with. If that's all you were shooting for, the 325's out of the box would do it no problem.

Mayor, sounds like a great build, and is right where it should be on power with the components you used. Obviously there's a fair bit of power potential left with a cam swap, given the cubes and compression. But, realistically do you need any more? It will be a very reliable combo I'm sure.

:food-smiley-007::food-smiley-007::food-smiley-007::food-smiley-007::food-smiley-007:

It's cold here today

My results
565 cu in, 9.3 comp., n/a efi 759@ 6400. Fully dressed with wet exhaust.

I boat at Mississinewa Reservoir nearly every weekend and Cumberland once or twice a year. At 78mph I am by no means the fastest boat at Mississinewa.

details on this build or did I miss them earlier in the post?

To save people looking it up:

Comp Cam #11-461-8
Intake Duration at 050 inch Lift: 254
Exhaust Duration at 050 inch Lift: 260
Duration at 050 inch Lift: 254 int./260 exh.
Advertised Intake Duration: 308
Advertised Exhaust Duration: 314
Advertised Duration: 308 int./314 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.575 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.575 in.
Valve Lift with Factory Rocker Arm Ratio: 0.575 int./0.575 exh.
Lobe Separation (degrees): 112

Wow. Just looked it up. Never even knew it was there. We got a place on Shafer lake. I'll have to check that out sometime

I agree, I think something in the .660 lift range would free up alot of power.

4.25x 4.600, Brodix -2plus heads cnc ported by rsd. crower 1.8 ss shaft rockers, Hogan sheetmetal intake, custom mercury racing 525 efi throttle body, Whipple tuned mercury computer, Hardin cyclone headers with Gil tails.

Mr mayor, how was your service with your engine builder? I currently use a guy in indy but I am looking for a little closer shop. I met you a couple of years ago at Cumberland poker run we were at wolf creek with Tim & Terry. Fred.

Should've used a 741 cam. It's this decades 3/4 race cam from what I hear lol

Screw it. Let's go 12.5:1 with a 502 mag cam and some peanut ports. Should be great pump gas poker run engine. esp with a nice leftover mix of 6 month old gas come spring. Lock the timing at 38 and have fun. :drool1:

:hitfan::crazy:

Really
You've done this combo?what compr and rough cam spec?

Why is everyone so obsessed with using an RV cam? I mean at least use something that has a nice idle and doesn't sound like an RV...

Top notch

Yessir, 9.8 to 1, 89 octane, similar sized cam to what you're running, maybe a hair smaller. 2000cfm throttle body, Holley efi intake. It was a low rpm deal, made 770hp. I built a 600" with AFR 305's last year. I wouldn't try to argue with anyone that those are the right heads for a 600" motor, but it worked really well for it's application, and the throttle response was nothing short of violent. It made 705hp and 740 tq through a set of Dana's. I do a lot of engines for big white water jet boats that have a very narrow efficient rpm range so I experiment a lot with different combos. When the pump manufacturers are designing new impellers, they use a shaft dyno to calculate the KW absorption of the impeller. My dyno numbers always match the numbers in the boat. The 357's are a killer head, and a perfect match for a 598 if, in my opinion, you were shooting for 850-900hp. I was just saying that on an engine that mild, I couldn't see spending the money on them. I'd go with cheaper heads and buy shaft rockers instead. :)

https://youtube.com/watch?v=I1XC7qqFY9E

Thanks and true for my boat and drive it is plenty and hope it last. I can't keep buying my wife anniversary gifts this expensive.

how are you getting away with 89 octane at 9.8:1 without a "kaboom"?

I am running 10 to 1 on 89 - have for years. I only run 93 now because Sam's Club sells it for the same cost as 89. I do have the block zero decked. ( tight quench )

For the guys running 10:1 compression or higher, what kind of cranking pressures are you seeing on a gauge?

Tcl has like 50+ cells
:D

10.7:1 130psi cranking pressure. Will not run on 93. I'd say it has a pretty tight quench due to signs of Pistons slightly touching heads.

Quote Originally Posted by HaxbySpeed View Post
Yessir, 9.8 to 1, 89 octane

That's shocking --- and great to hear.

I have been in conversations regarding rebuilding my carb'd merc motors, which started off as 500 HP's. I have been told to stay under 9.5:1 with aluminum heads and less for steel. i have been known to run a boat hard from time to time and have been warned about not running enough "octane" vs compression.

Not to hijack the thread, but I would appreciate your feedback regarding how you are eliminating detonation at RPM, even with knock sensors, which will be going into the rebuild, at that high of compression. Lastly, I have been thinking about converting these motors to EFI's. I know there is only up-side to doing it, I just don't know if I will see enough upside for this boat.

Is there a different thinking on compression with a carb'd vs EFI set-up? My other boats have all been EFI's so the carb'd thing was new to me with this boat, which made it interesting (esp. to learn how the old school guys did it) -- LOL :-)


Thanks, in advance, for your feedback,

Joe

My engines are 10 to 1 and turn 6000 RPM - never any signs of knock. I am running aluminum heads. I am building a 598 and plan on being at least 10 to 1 NA - EFI. I will have knock sensors on that motor. But I will be running 93 octane. No unnecessary sharp edges in the combustion chamber and zero decked.

I too am interested in these 10:1 or higher N/A setups. I've never tried it, and never recommended it, basically because I was too scared too. I also was always told/taught, to stay conservative on compression in a marine engine. Mostly around here, the guys I boat with have larger boats, being on lake michigan. Wide open throttle run time, can be extreme. Some of the guys I know will run their boats at 6000RPM, for 20-30 miles without pulling back. The few guys I know who ran 10:1 or more on these engines, had a hard time keeping them together. Whether it was based on their tune, cam choice, or lots of other possible variables, I dont really know. Lots of marina's here dont have 93 octane. I always felt the power from more compression, wasnt worth the hassle of having to find 93 octane. Now, bolting a blower on that might net you 100-200HP more, to me is worth having to seek out 93 octane. But 20-30hp to do so, imo, isnt worth it. To me at least. 25hp a side in a 38 Cig or 42 Fountain, is probably 1-2mph top speed gain. I'd rather lose the 2mph, be able to run lesser octane, or simply have a little safety factor on those long wot runs. Just guessing on the power difference as well, maybe its 50hp, or 75hp??

That was my theory. However, it may be totally incorrect, and my ears are always open. Seems like there are some guys out there running high compression with good results.

Joe, they detonate long before 6000 rpm. I think 3000 is a lot hArder on them than 6000. 1 point in compression will net about 3% increase in power not much. But as you know compression supports a bigger cam and that opens up more power in the combination. I can get race gas for $6-7/ gallon if I do a 20% mix I end up with almost 96 octane. Runs about $80 more per tank. Not to bad. The octane in race gas does degrade but at a much slower rate than ethanol fuel. The extra cost per tank is well worth it in my opinion and it smells real nice when your pulling up at the local hot spots.

Lugging.

More compression can use more cam and thus peak power rpm will go up.

Too many freakin people prop for freakin stock rpm of 5200. Lug, lug, lug.

That's #1.

Engine. obviously cooling system flow and temp, head material, combustion chamber design, piston dome design, clearances, plus, and tune can all make a difference.

A properly designed driving helmet can help with aerodynamics and reduce the lugging effect.

Another reason why a fully programmable ignition curve is so beneficial. Being able to customize your curve around your torque curve as opposed to being locked at full advance allows you to run higher compression without the risk of detonation around the torque peak.