Carb guys..
 

Im running a stroked 496 dart alm 310cc heads elderbrock air gap intake full roller motor.Motor dynod wet with acceseries @500 hp 600 trq.peak hp was at 3800.Motor runs and pulls great to about 4800 4900 then thats it. First question Im running a Barry Grant sea demon 750 is this enough carb? Would a carb spacer change my peak hp, trq rpm to a higher rpm. Would I gain any hp overall.If so what combo, Ive read on here people using 2 in spacers one with 4 holes then a open hole.With the hole type should they be the same size as the carb mine are 1.4 dia.

Did you dyno with that carb ? Seems a little small to me . Or try one size smaller prop.

Peak HP @ 3800?? this is a typo, right?

You need a bigger carb.

What boat is it in? What prop are you running? 3800 rpm hp peak on the dyno sounds kind of low. If you say it pulls great to 4900 than it sounds like it's doing pretty good. I would think that combo would be better with a 850.

yes dynod with that carb tried 23 mirage rpm about 5k 25 mirage 48 49. Also stock merc manifolds,I know these may be holding it back. Boat pulls strong with either prop pulls from 3800 to 4800 in 2 seconds then kinda just sits there. I dont need anymore hole shot (TRS drives)just top end. Boat cruises around 45 great, tops about 64Thought if I could easly change the sweet spot higher Id cruise arnd 50 55 top arnd 70 75 Respectable for a old 40 footer

No not a typo motor has lots of trq low. I know the cam needs to be set different but thought carb spacers might help till winter.

More speed equals more prop which takes more power. Not to be smart but it takes a lot of HP to make that much fiberglass go 75 mph. And I think you will find that the peak torque was at 3800 not peak hp.

75 mph
 

my friend had a 1986 Fountain ICBM 12m with twin 454 single carb blown engines and the lower ends with no paint and no prop hub exhaust . probably 550 each maybe 625hp and that did 82mph

No disrespect, but you are not going to see those speeds in that boat with that power.

Carbs
 

None taken ... What I still realy want to know is about carb spacer will it move my power band or increase my rpm? Im positive if I could get 300 400 more rpm or move the peak hp it will run faster 64 65 gps now 5 more isint impossable

All the carb spacers in the world will not get you 5 more mph. Check in the last issue of powerboating mag , Teague had an article on carb spacers.

try a good 850DP and then with a 1" spacer...should pick it up

I have about the same motor. Adding a 2" spacer pulled 20 more hp (back to back pulls). I tried a 750 and was only pulling 715 cfm through the carb. Isn't there a cfm reading on the dyno sheet? I put on a 850 and pulled 757 cfm. I can't remember how many extra hp's that added, but was enough for me to throw down on a couple barry grant 830 mighty demon's. I'm happy now.

IMHO, if you can get your hands on this Holly 4150HP, works great on 500 C.I. motors. Don't be fooled by the size. This is really an 850 body with a 750 throttle plate. The lower rpm of your motor will really like the increase in velocity. Course, greatly depends on the cam you have. Do you have your cam card?
http://www.summitracing.com/parts/HLY-0-80496-1/

You are wasting your time until you get new exhaust.