What is wrong
 

Ok so we just repowered my boat. 94 sunsation dominator. Bravo 26. 6 1/2 deep drives. Last year we ran 489 9.6:1 comp 284hr cam 230/236 .547/.547 lift l29 heads with stamped rockers air gap intake and quick fuel 750 carb. Pertronix marine distributors. Max rpm was 5100 at 72mph with roughly 400hp @28 max timing

This year we have 489 8.2:1 comp crane 741 enginequest 320 heads, crane gold rockers, victor jr intake, quick fuel 750, kn filters with stub stacks, pertronix distributors. Max rpm 5100 at 72 mph. Timing at 34 currently afr 12.5 Wth is going on. We should have 120-150 more hp per side. Im all ears

I had to read that twice looking for which blower. Why 8.2:1?

We are set up to run blowers in the future. It is a hard runner, much quicker than previous year build. My peak should be at 55-5600. Do I need to bump timing up to 38-40?

The first set up was doing pretty well considering the use of truck heads . Its hard to make big power even at 489 cubes , with 8 to 1 compression ratio. But for mow you should def be safe with 87 octane until the blowers go on

Dropped compression almost a point and a half and put in a bigger cam and went to a single plane.

Prob needs more carb.

Dropped compression is minor as it is only a 3% difference in power per point. Old heads flowed 255 at .600. Now we are at like 345. Also I took into account of compression when comparing to 525efi which is 8.75:1. Same cam. Way better heads. Weak carb. Im almost thinking carb and timing increase. Does the general rule of 1 degree advance equals 1 percent hp gain on bbc

How big griff

Got a buddy with 489's with Brodix BB-2 heads. Not sure on cam. Merlin intake. 850 Holley 4150's with the towers cut off. 35- 36 degrees timing. 89 octane. 5,200 - 5.300 RPM. Pushes a '96 303 SR-1 to 75 - 77 MPH. Way less efficient and heavier hull than your Dominator.

How far can i lean on my timing with 8.2:1. I am running 87 now but am not afraid to run 91. Also im running comp lifters set at 3/4 preload. Could that be an issue

I'm not sure how sensitive the 741 cam is to comp and realize it's used in engines less than recommended comp (10-12:1) however wondering if you degreed the cams or just installed straight up? Try some 25 p props to get the rpm's up closer fo 5,500 and I would imagine the engines will be happier and you'll gain speed. Personnly I think you would be better with the airgap but just get the blower on and be done with it.

Btw I wouldn't take the timing past 35-36 deg and doubt your valve lash is an issue. 1/4-3/4 turn past 0 lash should be fine. I total see what your getting at but yet think your a little optimistic with your expected gains of 120 to 150 hp. Heads out of the box or ported and flowed? Also did you install new rings or stay out of the bottom end? Both engines the same?

Lower compression with higher flow seems like it would be a bit of a dog without a huffer to help push it through as you have even less cylinder vacuum to gulp in a bigger bucket of fuel, but I'd say that your carb is your limiter.

Cam installed straight up. Heads box stock with corect crane sorings etc. ferrea valves. Redid entire bottom end. New rings. Low tension oil 12lb. Comp ring gap .021.

Also if you get a chance try a larger carb. anything larger that you could potentially borrow and try would cut to the chase. I nearly did the same as you with low compression 555 builds for near future 871's but decided to wait and do it all at once cause I figured I'd be chasing power that I simply wouldn't likely achieve.

Although you can read up on smittys low compression build and pick up on something there. It's a good thread but different CI build.

How much time do you have on it? Rings seated yet? What kind did you use?

2.5 hours 90% over 4k rpm. Total seal rings. I would say rings are seated. It was wide open at one point for 8-10 minutes

Just for the heck of it take a comp test on a couple cylinders and see where you at. I know you probably don't want to but see if you can borrow some smaller wheels. If had had to bet you'll gain worthy speed.

I have mirage 25 std and 27 plus'. 25 mirages bite out of hole good. 27 not a chance in hell. Takes 500 yards and alot of crafty throttle. Problem with both is when i get in rough water at under 35mph the bow shoots for the moon an cavitate then regrabs then cavitates then regrabs. So basically have to stop and restart. Thats why i went 4 blade even with deep drives

Sounds like you have not dyno tuned so I would at least add some O2 sensors and tune on the water, but don't forget to also properly read the plugs.

Thought op said 12.5 afr. Plug reading always a must regardless though.

We have wideband on it.

Havent dine plug reading. That is next step when leaning her out a hair

Be careful 12.5 is right near the comfy zone. new plugs - wot - pull tethers.

When you plan on installing blowers?

As soon as i find a good deal I can afford. Also. Plug gap is .045 7 heat range ngk

If your plan is to put huffers on, then do it. That's where your HP is, Anything else is just chasing your tail in circles. It's hard to build a low comp motor and get the HP out of it. That's what the blowers are for. IMHO what you have is 1/2 of a build.

You'll be happy you built low comp builds after you strap the blowers on. You'll be able to safely throw boost to them and make some good power. Just gotta bite the bullet for a while. You just need to keep in mind that the new components will soon compliment your builds.

I see you have a set for sale. We run a sherwood crank mount waterpump can that be used with that setup or does it require the mercruiser style

I've only seen one of those crank mount pumps on an older boat I owned and from I recall I don't think they would.

Your compression is too low , your cam is bleeding off what little cyl pressure you have . Iits not timing , carb size, tuning or anything else . You not only knocked 1.5 points of static compression but you also severely lowered your dynamic compression by a later closing intake valve .

Than why does a 525efi with the same cam work so well at 8.75:1. I am technucally at 8.27:1. Nothing major. The previous 9.6:1 is irrellevant considering the heads flowed as much as a pinto running on 2 cylinders. Lol. Sure the low end torque was great. But top end sucked. On old heads from 4500 to 5100 rpm rise came to a crawl. Sure it got there but took forever. New engine instant. I may have figured it out. I loaned the distributors to a buddy to try out on his twins while mine was down. They are pertronix ignitir 3 with rev limiters. I asked him if he messed with them and he said yes but didnt recall what rpm he set them to. Will find out tonight.

the facts billyboats stated are all contributing facts to the poor performance of these engines,also without degree checking of the cam,s position with the crank the specs on the cam are not factual.all those specs are based on the cam being properly phased with the crank.lets say your cam is 5 deg retarted from correct phasing,now you are bleeding off even more compression down low,it might make power at 6700 rpm but it can,t go past 5100 because it does not have the power to do so.mercury marine produces an engine that can run on 87 octane fuel,only has 8.75 c/r and uses a pos edelbrock head.with the same cam,10/1 cr and a good cylinder head 600 plus hp would be all day every day.

If I remember right the silver spring doesn't fully advance until 5 or 6k. However if you cked timing that wouldn't be an issue. Go to pertronix site and go to HEI distributors and find your model and download. This is just for your own info but should know what you have going on if you had a friend messing around with them since you used last. People have a tendency to change things just to see what happens but in reality don't have a clue. So regardless make sure you know what you have. Just a FYI.

Silver spring all in by 3500. Well checked rev limiters or at least tried to. When i loaned them to him they were set with limiters off he had them set somewhere because they were not fully clockwise. Problem is the pos will not go into relearn rev limiter mode on either. FML. No led blink. Nothing. So two new ignitor 3. I could literally burn this piece of crap to the ground right now im so pissed

Hang in there it only seems to get worse. Lol.

Sounds like sime motivational speeches I gave in the military.

Does anyone know of a propshaft dyno in AZ

Carbs are too small, IMO. They need 850's atleast.

I would check that the timing is good, plugs look fine, and run the b!tch. Save money for blowers and then start the chit all over again LOL

Pertronix is sending two new ignitor 3 modules. They said it sounds to them like the modules are bad sense the leds on both do not respond to adjustment. We will see.

Blowers.... Rembember you get to do the distributor/ign thing all over again when you go SC. Another 1k per side. Fun fun.