Originally Posted by vintage chromoly (Post 4482337)

Tim, call my buddy at On The Bumper Performance. 440-479-9420 Just built a 512 BBC 830 cfm carb 9.5 compression and made 676 hp at 6200 rpm 602 ftlbs torque at 4800 rpmwith 15 year old brodix heads. They will check everything out and verify compression, head flow and Spec you custom cams.

Originally Posted by Gimme Fuel (Post 4482111)

I know with my Bob M. 548 combo. (10.2 CR, afr 335 cnc heads, 454-R dom intake with 2100 cft TB. Holley efi. speculated 730-760 hp @6300 by Bob, I never dynoed) it was very touchy with prop pitch. I thought I needed to be somewhere around 25-26p prop with my 253 checkmate...ran it first year, thought it was a dog and was disappointed but was happy to be boating. 73-75 mph struggling to get 5500 rpm. End of that first year found out machinist pooched hone job and bores were quite shiny after 20 hours. Redo .030 over, add a lil extra compression, great ring package...new machinist. Put back in boat, turned the same prop the same rpm......dissapointed. Lackluster acceleration. Even tried a 24p with little improvement.

Now, get a wild hair on my azz to throw a seemingly tiny 23p prop on the boat. Guess what. Instantly screams to 6000 rpm in a heartbeat and climbs past 6300 in short order. Boat passes 80 mph within a mile. Prop was far from ideal (nicks and zero cupping hydromotive qiv) and was just a test, full gear and full fuel tank. Wound up running that prop rest of season with big ole grin on my face. Boat broke 80 mph which takes 700 minimum in that hull plus I keep a ton of gear and supplies in boat at all times, I never run "light." Could scream past friend's similar boat with 600sc merc.

Moral of the story, engine was very sensitive to small change in prop loading and I was my worst enemy. That engine wanted RPM and made its power up there, I wasn't letting it get there with slightly too big props.

Originally Posted by HaxbySpeed (Post 4482423)

How close are your custom cam specs to this one Tim? [ATTACH=CONFIG]559497[/ATTACH]

Originally Posted by getrdunn (Post 4482415)

In all reality you should have been propping for 6k rpm plus to start when you spec a build for peak hp @ 6,300. I would guess at hp @ 5,500 you'd be down well over 100 hp. If I'm not mistaking I recall another post by FF and power from 5,500 to 6,000 was minimal to none so propping for anything more than 5,500 wouldn't be beneficial.

Btw that is a spectacular hp build for a 548. Like you said though, you know what it takes to push your hull over 80. In comparison to valakos 27 fountain that has 565 making 784 and runs 98-100 mph. Definitely a little slippery hull though.

Also to help OP out it would be nice if you could post your cam specs. Lift and duration anyway. 242/248 duration??? Just a guess

Originally Posted by getrdunn (Post 4482418)

I may have missed it somewhere but did Bob spec the cam based on the intake and carb you have on builds? Something just seems restricted and I honestly don't believe its duration and your lift is very respectable. Those cams should not be done at 5,500. See if someone has a set of 1.8 rockers you can try on one engine just to see if it likes more cam. The heads will have no problem flow with the extra lift that's for sure. That will give you a little more duration as well. Not saying long term fix due to possible valvetrain stability but I'd try them in a heartbeat.

Also can you post cam card. Curious to see valve opening and closing timing. I know to some custom grinds are like sacred knowledge but considering...

Originally Posted by HaxbySpeed (Post 4482423)

How close are your custom cam specs to this one Tim? [ATTACH=CONFIG]559497[/ATTACH]