what gives?

[oilfieldtrash]

i have an 18 ft nordic bubble deck. this past winter i went threw the motor and installed new bearings and rings a cam and a set of closed chamber heads off a 396. i had the heads built with new valves, new springs and roller rockers. installed a new set of rewarder ot headers and a new 850 cfm holley dp. the engine is a 454 bored 30 over. my question is that i still cant turn it past about 4500 rpm, last year with my 30 year old motor i was pulling 4300 rpm. what gives? i now my pump is worn out, it also is 30 years old without any overhauls sense new. i now this because i got the boat from the original owner. any help or a point in the right direction i would appreciate it greatly!

[ap67et10]

what heads were on it before? what kind of compression? how big a cam? it kind of sound like the engine stuff you did might not have increased your power much...typically a refresh doesn't gain a lot of power unless the thing has some major blowby issues and is a complete pig...but if you didn't really step it up with the heads and cam and intake (what intake?) you may have only gained 30-40 horse which shows with the rpm increase. maybe take a look at the impeller charts, it should give you a rough estimate of the power your boat has. the only other thing that would cause low rpm is poor engine runability...is it misfiring or falling on its face or doing anything that shows its not tuned right and low on power?
AP

[Moneypitt]

Too fat......Over carbed, big time....Try a 650 and check the difference......MP

[oilfieldtrash]

what heads were on it before? what kind of compression? how big a cam? it kind of sound like the engine stuff you did might not have increased your power much...typically a refresh doesn't gain a lot of power unless the thing has some major blowby issues and is a complete pig...but if you didn't really step it up with the heads and cam and intake (what intake?) you may have only gained 30-40 horse which shows with the rpm increase. maybe take a look at the impeller charts, it should give you a rough estimate of the power your boat has. the only other thing that would cause low rpm is poor engine runability...is it misfiring or falling on its face or doing anything that shows its not tuned right and low on power?
AP
i am not to sure of the compression they are flat top pistons with closed chsmber heads. the intake is a old style edelbrock torker the cam is comp cam part # 11-209-3. valve lift is I .507 E .531. the other engine was clean and reliable it ran every weekend i just figured with the heads, cam, headers, and carb i would pick up a little more then that. the other heads were open chamber stock late 70's

[oilfieldtrash]

Too fat......Over carbed, big time....Try a 650 and check the difference......MP
the first time i took it out i ran a 700 holley it ran like crap it would not pull on the top and mid range was weak. i put the 850 on saturday and went out and it ran alot better pulled hard all the way to the top out of about 4500 rpm. it feels like there is more there, it just would go past 4500

[Moneypitt]

the first time i took it out i ran a 700 holley it ran like crap it would not pull on the top and mid range was weak. i put the 850 on saturday and went out and it ran alot better pulled hard all the way to the top out of about 4500 rpm. it feels like there is more there, it just would go past 4500
Regardless, the 850 is too big. That motor can't use that much air/fuel. What is the list # on the 700???????............MP

[oilfieldtrash]

Regardless, the 850 is too big. That motor can't use that much air/fuel. What is the list # on the 700???????............MP
the # on the 700 is 4778-2. ok then why doe it run better with the 850? i am new to this so any knowledge i gain is knowledge i didnt have.
thanks casey

[gbelt]

What are you running for ignition? Is it all in top shape? What kind of advance are you running? Fresh fuel? Did you degree the cam? Just some other things to consider.

[oilfieldtrash]

What are you running for ignition? Is it all in top shape? What kind of advance are you running? Fresh fuel? Did you degree the cam? Just some other things to consider.
i am running an HEI distributor with msd wires all in good condition. the shop that did my motor work said to set the timing at 32 deg. total. the fuel is fresh 91 octane. and no i did not degree the cam. the guy who did my motor work said there was no need to because this was just a mild motor.
thanks casey

[Moneypitt]

the # on the 700 is 4778-2. ok then why doe it run better with the 850? i am new to this so any knowledge i gain is knowledge i didnt have.
thanks casey
I'm guessing the 700 had some issues the 850 doesn't have. The motor wouldn't run like shit with the 700, it might lay down a little around 6500 if it were truly starving for fuel. The 850 seems to run better because the extra fuel is crutching the motor, simular to a manual choke on a Chevy 6 while cruising at low RPMs......As mentioned, alot can be said for ignition timing, camshaft location, compression ratio, etc etc etc......Again, IMO, 850 is too much fuel for a 460 turning under 5K.............However, IF the 850 makes the boat drivable, and you're having fun, go for it, enjoy..........MP

[oilfieldtrash]

I'm guessing the 700 had some issues the 850 doesn't have. The motor wouldn't run like shit with the 700, it might lay down a little around 6500 if it were truly starving for fuel. The 850 seems to run better because the extra fuel is crutching the motor, simular to a manual choke on a Chevy 6 while cruising at low RPMs......As mentioned, alot can be said for ignition timing, camshaft location, compression ratio, etc etc etc......Again, IMO, 850 is too much fuel for a 460 turning under 5K.............However, IF the 850 makes the boat drivable, and you're having fun, go for it, enjoy..........MP
thanks man i am goin to have to take another look at the 700. i guess i am going to have to find a better combo to go with i just figured that i would see more out of the combo i put together this winter. anybody have any ideas or a recipe for a good combo that will build good power and turn some r's. please help im really disappointed with my present situation.

[gbelt]

How old is the distributor? Does it have a solid 12v source? I know when I've done that swap in a car I always use a 10 gauge wire to feed it because they draw a lot of power, if you have something smaller it may have worked with your old setup since you were only running 4300 or so, maybe it needs a little more. Are the contacts on the module and those conecting to the coil clean? Any wobble to the shaft? Stock modules seem to be good for about 5000-5500 rpm, if you had a spare I'd throw that in and give it a try. Me personally would try bumping the timing to 34 or 36, clean off all the connections that have to do with the ignition, just remember to check the plugs because I doubt you'd hear any detonation with the OT pipes.

[oilfieldtrash]

How old is the distributor? Does it have a solid 12v source? I know when I've done that swap in a car I always use a 10 gauge wire to feed it because they draw a lot of power, if you have something smaller it may have worked with your old setup since you were only running 4300 or so, maybe it needs a little more. Are the contacts on the module and those conecting to the coil clean? Any wobble to the shaft? Stock modules seem to be good for about 5000-5500 rpm, if you had a spare I'd throw that in and give it a try. Me personally would try bumping the timing to 34 or 36, clean off all the connections that have to do with the ignition, just remember to check the plugs because I doubt you'd hear any detonation with the OT pipes.
cool thanks for the info. i was thinking about buying a new msd or dui distributor. the one that is in the boat is old and it is a car one any suggustions on a new one?

[gbelt]

You can buy a brand new Mallory HEI from Summit for about 150, it's not a marine unit but then again neither is the one you have now. I have a Unilite in my boat, it's been reliable, only had to replace the module once in 15 years and that was because of a bad ground, but to be honest I'd rather have the HEI just to clean up the wiring. A good thing about the HEI is you can get parts for them reasonably priced just about anywhere, I'd have to hunt to find the Unilite rotor that my distributor takes (so I carry a spare). You can't go wrong with MSD, I don't have any experience with DUI systems. For the price that Mallory is going to be hard to beat since it's complete with coil. Good luck, your combination looks sound and reliable, probably just needs a bit of tweaking on the spark and fuel to get some more out of it.

[squirt]

What size impeller are you turnning and what pump??????? There is no way to know if 4500rpm is a good number for your motor without knowing just how much load is on the motor. It could be ok for a AA, not so good for an A, and piss poor for a B. Also make sure your tach reads right. I'd bump the timming like suggested to 34-36 deg. It takes about 340 hp to spin a good A impeller to 4700 and it looks like you have a little more cam than a stocker. Somethig is not right here.
Don

[oilfieldtrash]

What size impeller are you turnning and what pump??????? There is no way to know if 4500rpm is a good number for your motor without knowing just how much load is on the motor. It could be ok for a AA, not so good for an A, and piss poor for a B. Also make sure your tach reads right. I'd bump the timming like suggested to 34-36 deg. It takes about 340 hp to spin a good A impeller to 4700 and it looks like you have a little more cam than a stocker. Somethig is not right here.
Don
i have a berk 12JG with an A impeller. the cam is not huge but it is bigger than stock. i will try bumping up the timing and see what happens. would rebuilding the pump and installing a place divertor help the situation?
thanks for the info. o-ya how would cheak the tach to make sure it is reading right?
casey

[BrendellaJet]

i have a berk 12JG with an A impeller. the cam is not huge but it is bigger than stock. i will try bumping up the timing and see what happens. would rebuilding the pump and installing a place divertor help the situation?
thanks for the info. o-ya how would cheak the tach to make sure it is reading right?
casey
Might want to talk to some of the resident desktop dyno gurus and see if we can get an estimate on the power you are making. Jet pumps take horsepower to turn. FYI, guys running jetboat specific motors with 700 hp turn their pumps in the6000-6200 range, that gives you an idea of how hard they are to turn...
If you want more speed, gotta make more power. Rebuilding the pump will probably lower RPMs some, but may produce more speed. Definitely go with a place diverter if you dont already have one, They are great for trimming your boat and are fun to play with too.

[squirt]

i have a berk 12JG with an A impeller. the cam is not huge but it is bigger than stock. i will try bumping up the timing and see what happens. would rebuilding the pump and installing a place divertor help the situation?
thanks for the info. o-ya how would cheak the tach to make sure it is reading right?
casey
No rebuilding a pump usually tightens things up and will decrease rpm further but if ya need a rebuild ya need one. A place diverter is a good thing but won't effect how your engine spins the pump. RPMs are low for a BBC and that impeller I would think 4800-4900 would be closer, even if you were running 8-1 flat tops and closed chambers. You can check the tach with a know source, a verified tach/ dwell meter, an old dist machine for curving dists., a MSD ign tester, or a speedo shop. Did you check to see that the secondaries are opening all the way at WOT on that carb?????

[oilfieldtrash]

Might want to talk to some of the resident desktop dyno gurus and see if we can get an estimate on the power you are making. Jet pumps take horsepower to turn. FYI, guys running jetboat specific motors with 700 hp turn their pumps in the6000-6200 range, that gives you an idea of how hard they are to turn...
If you want more speed, gotta make more power. Rebuilding the pump will probably lower RPMs some, but may produce more speed. Definitely go with a place diverter if you dont already have one, They are great for trimming your boat and are fun to play with too.
who on here is handy with the desktop dyno? how much hp does it take to turn an A impeller to 4500-4600 rpm?

[oilfieldtrash]

No rebuilding a pump usually tightens things up and will decrease rpm further but if ya need a rebuild ya need one. A place diverter is a good thing but won't effect how your engine spins the pump. RPMs are low for a BBC and that impeller I would think 4800-4900 would be closer, even if you were running 8-1 flat tops and closed chambers. You can check the tach with a know source, a verified tach/ dwell meter, an old dist machine for curving dists., a MSD ign tester, or a speedo shop. Did you check to see that the secondaries are opening all the way at WOT on that carb?????
ya i know if i rebuild the pump it will make it more efficant and harder to turn more power needed iam going to order a new distributor and check the tach i figured i would make 400 - 450 horse with set up i am running. is that out of the question?

[Cas]

ya i know if i rebuild the pump it will make it more efficant and harder to turn more power needed iam going to order a new distributor and check the tach i figured i would make 400 - 450 horse with set up i am running. is that out of the question?
it depends on "where" the engine is making that power. If the 450hp is up at 5600 and 320 at 4500, it will never use the 450 with an A impeller.
If you have the engine specs, all the cam specs, head specs and info for the intake manifold and carb, I can use the Desktop Dyno to help you out.

[squirt]

Well just guessing but 400-450 would seem within reason just don't have 1st hand experience with closed chambers on a jet application but should be ok.
Unfortunitly your not seeing close to that now. Check timing and make sure carb is opening, also what altitude are you using the boat at

[oilfieldtrash]

Well just guessing but 400-450 would seem within reason just don't have 1st hand experience with closed chambers on a jet application but should be ok.
Unfortunitly your not seeing close to that now. Check timing and make sure carb is opening, also what altitude are you using the boat at
i will cheak the carb and bump up the timing. im @ about 6200 ft above sea level. i dont now much about heads may be i will have the open chambers built and see were that takes me what do you think

[squirt]

i will cheak the carb and bump up the timing. im @ about 6200 ft above sea level. i dont now much about heads may be i will have the open chambers built and see were that takes me what do you think
Bingo!!!!!!!!!!!!!!
6200ft 4500rpm might just be the key...........play with the jets on that carb I think your probably fat;)

[oilfieldtrash]

Bingo!!!!!!!!!!!!!!
6200ft 4500rpm might just be the key...........play with the jets on that carb I think your probably fat;)
do you think i should ditch the 850 or try to work with it? i also have a 700 maybe try messing with it.
the 850 has 78 in the primarys and 83 in the seconders. i am not sure about the jets in the 700 i will have to pull the bowls and check.
what do you think i might see in havasu?

[Sleeper CP]

6200 ft Bingo, we have a winner. Hell you might need a 150 shot of Nos to get to 5,500 Rpm's. Check your jets, you might want to take 4 sizes out and see what happen. That engine will use approx. 730 cfm's at 5,500 rpm's, but you'll never get there at that altitude.
Sleeper CP

[oilfieldtrash]

6200 ft Bingo, we have a winner. Hell you might need a 150 shot of Nos to get to 5,500 Rpm's. Check your jets, you might want to take 4 sizes out and see what happen. That engine will use approx. 730 cfm's at 5,500 rpm's, but you'll never get there at that altitude.
Sleeper CP
thanks for the info. should i go back to 700 or stay with the 850

[Sleeper CP]

Check out the thread " What's the differance between A,B and C impellers"
I just brought it back up post's #4 & 23. See the Berkley HP chart an A impeller uses just 300 HP to turn 4,500 rpm's. At 6,200 ft that might be all you have. It's a shame that you didn't have the cam degreed in, but Comp cams are useally pretty true but you never know. I put a cam in a Smblk Ford 16 years ago and just lined up the dot's. The thing ran liked crap, no lower end at all and wouldn't pull rpm either. Pulled it apart degreed the cam in it was off by 8 degree's. It was a different engine when I got it back on the road. Your problem is probably altitude relate though.
Sleeper CP

[Sleeper CP]

If the 850 is working I wouldn't sweat the carb right now. But it does sound like the 700 might need some work on it. When you have a chance get it re-built and as someone else said make sure you have Wide Open throttle with your carbs. In any case you might want to have that 30 yr. old pump looked at and maybe see about an A/B cut or even a B cut.
Sleeper CP

[Moneypitt]

That could play a HUGE role in your quest for RPMs.....At that altitude 700 should be plenty of carb.......If you ever bring it out of the mountains be prepared to be quite lean if it runs up there, regardless of the carb..........MP

[ap67et10]

i had a boat that spun an A impeller 5200 rpm at just about sea level. took it up to about 7000 ft. and only saw about 4600. And that was an engine with an efi setup so it adjusted to the thin air perfectly but just because the air is so much thinner you have less pressure, and atmospheric pressure is the same as if you had a blower sitting on top...pressure is pressure and your engine can only suck so much in...the pressure also helps push it in. if you had an engine with a blower on 10lbs and lowered it to 6lbs you would lose power..thats what you are up against you make less power because you have less help from nature than if you were down lower. you will run fatter up at that level then if you went down, but check your plugs...they will tell you right away how its running and don't start changing jets if you don't need to. if they're a nice golden brown just have fun cause its runnning good and your up against thin air so 4500 is really pretty good. and if the 850 runs better then run it. the 850 is a rating of cfm and its saying that carb has the ability to flow that much air. If you engine flows 600 cfm at wide open throttle (example) then thats all it flows... having a 700 or 850 makes no difference other than it may change the velocity of the air at various rpms and other little crap that probably doesn't pertain to you so much. if its jetted good and it runs better with the 850 than 700 and your happy with gas milage you have no reason to change your carb, so keep it. hope this helps you out in the mist of so many opinions.
AP

[oilfieldtrash]

thanks for the help guys! i may have to try a new recipe for an engine next winter to make some good power were im at! anybody with some ideas? i plan on makin a trip down to some lower elevation towards the end of the summer any have any recommendations for jetboat freindly lakes?
Thanks again
Casey

[ap67et10]

forced induction is the only way to go for you. go spend a little money on a blower...nothin fancy you only need a few lbs of boost to get you right where you will want to be...then you won't really have to worry about loosing all that much up high. And if you go with like 6-7 lbs you won't need to do any major engine upgrades...just make sure you have forged pistons...with lower compression of course.
AP