[crmax]

I have a 20' that is on the heavy side also 3500 lbs dry, a 310 hp 454 with a 23" prop she will do 64.6 mph on the gps @4750 rpm

the boat you have is fine, you should be in the 58 mph are with a 21" prop

 

[DonMan]

I think you are actually pretty close to your max potential. A 19" pitch is about all a small block can spin to any real rpms. I don`t think you`ll be able to get any rpm out of a 21" prop. Maybe I`m wrong......
Most of my experience is with big blocks. My last boat had a 240 hp 350 (Yamaha drive), 19' hull. I could only muster 4400 rpms with a 19 pitch 3-blade. My speed was right at 51 gps. This was a pretty light rig.

 

[crmax]

I think you are actually pretty close to your max potential. A 19" pitch is about all a small block can spin to any real rpms. I don`t think you`ll be able to get any rpm out of a 21" prop. Maybe I`m wrong......
Most of my experience is with big blocks. My last boat had a 240 hp 350 (Yamaha drive), 19' hull. I could only muster 4400 rpms with a 19 pitch 3-blade. My speed was right at 51 gps. This was a pretty light rig.

he has a warmed over 260 he has to be pushing around 300 hp at the crank

 

[DonMan]

he has a warmed over 260 he has to be pushing around 300 hp at the crank

It`s still a small block though.
A 300hp small block can`t match the torque of say, a 250hp big block. Of course, I don`t think you can build a big block with "only" 250hp, but for arguements sake, let`s say you can.
I know you`re comparing your 310hp against his 300hp, I don`t think it`s a valid comparison, you have a big block.
Does this make any sense?

 

[BCMSW]

I think you are actually pretty close to your max potential. A 19" pitch is about all a small block can spin to any real rpms. I don`t think you`ll be able to get any rpm out of a 21" prop. Maybe I`m wrong......
Most of my experience is with big blocks. My last boat had a 240 hp 350 (Yamaha drive), 19' hull. I could only muster 4400 rpms with a 19 pitch 3-blade. My speed was right at 51 gps. This was a pretty light rig.

I think you may be right. I found some other 211 Liberators with max speed listed on www.boattraderonline.com. One was powered by a 270 that listed 45 mph and the other is a 460/340 that lists 52 mph. I did touch 50 yesterday on the gps for a second, but most consistent runs were in the 49 range.(With a full tank of gas)
The thing that concerns me now is the lack of RPM @ wot. Will it damage the engine to run 4100 at WOT (I like the way the fourblade prop performs)? Or should I run a smaller diameter 14X19 and sacrifice some miles per hour for 4600 RPM. I also have a 14 1/2X18 Stiletto I need to get rehubbed and a friend is supposed to be bringing me a 14 1/2X19 Ballistic to try(I have been told they work well on the Liberators). I am still going to look for the maximum rpm for maximum top speed trade off.
Is the motor making power without getting it up in to the 4800-5200 range? The other 211 Liberator that he put the same motor in is a few years newer (maybe a lighter hull?) and is turning 5100 rpm +/- with an OMC outdrive in the upper 50's (I think the boat owner told me 58).

 

[Jerry G.]

Help!

BCMSW,

I think your in the ballpark as far as speed. My 1988 23' Powerplay weighs 4100 dry. With a warmed over small block w/ stock heads I managed 53 mph on gps with 50 gal, fuel. Prop is 14 1/4" 22P Turbo spinning 4500 at WOT. Last year I was running 4700 rpm with a 20P prop and 4200 with the 22p prop which was prior to engine mods which are similar to magnum specs.
Running only 4100 will stress your motor. I feel you can spin at least 4800 to 5000 with the right prop if the motor is right and you check out all the previous recommendations.
Julie at Trrottle Up can answer any Prop questions for you.
Hope my 2 cents helped.

Jerry G. aka " Raptureman"

 

[VillainIII]

A friend of mine had a 89 glastron 22' that ran 58 at 4600 rpms with a stock 350 mag. He was using a 19 pitch 3 blade (don't remember what brand).

 

[BCMSW]

Re: Help!

BCMSW,

I think your in the ballpark as far as speed. My 1988 23' Powerplay weighs 4100 dry. With a warmed over small block w/ stock heads I managed 53 mph on gps with 50 gal, fuel. Prop is 14 1/4" 22P Turbo spinning 4500 at WOT. Last year I was running 4700 rpm with a 20P prop and 4200 with the 22p prop which was prior to engine mods which are similar to magnum specs.
Running only 4100 will stress your motor. I feel you can spin at least 4800 to 5000 with the right prop if the motor is right and you check out all the previous recommendations.
Julie at Trrottle Up can answer any Prop questions for you.
Hope my 2 cents helped.

Jerry G. aka " Raptureman"

Thanks. Your Powerplay weighs 1100 lbs more than my Liberator. Compared to you spinning a 22 @ 4500 I am still lacking--I don't even think I could spin a 22 in the 4000 range. This motor is supposed to be Magnum specs too (or better) with better pistons, Vortech heads, high rise intake, and roller rockers. I am going to check with him again on the camshaft and see if he has a fuel pressure gauge I can use. I have tried everything else. Today, lighter on gas and with the Hill 4 blade 14 1/2X19 I am just hitting 50 @4100 by myself unless I was in to the wind and that dropped me in to the 49 mph range.
If I trim it up with the trailer button to where it almost blows out I can get it to turn 4500--not much more though, but with a considerable loss of speed. Could this just be because the outdrive is binding from being trimmed up so far?
I really don't think it is a prop question though. Maybe. My friend just offered his 21 Pitch Hi-5. I will probably try it this week if it gets nice to see what happens. But I just do not think that motor is making the power it should or there is something wrong with my hull. I am leaning toward the motor though.

 

[OldMagicfloat]

Be careful running overpropped! I just had to have my crank redone because of the same thing. It causes detonation problems and causes added stress to the main bearings. I would try a 17" with a little bigger dia. I run 22' sea ray with a 5.7 and ran 52 on gps with 4 people and 1/2 tank fuel. What kind of exhaust are you running? I know that the mag motors like to breathe alot. Also is the carb the same as the one on the old motor? If so you might want to have it checked out.

 

[cfm]

I agree with you guys.

It is harder on a motor under full load and a one speed transmission to berunning too low of an rpm.

Plus, you are losing big horsepower! A stock small block will make max hp between 4800-5000rpm.

A typical 300hp engine will have hp numbers similar to this:

3500rpm 225hp
4000rpm 257hp
4500rpm 281hp
5000rpm 298hp

Again, this is not your engine but an example to so you the power differences at different rpms. Why count on 300hp if you are only using 250hp?

Add to this - what if your motor is losing hp do to inproper tune? More lost hp. On mild small blocks I have seen anywhere from 0-30+hp gain from 'super tuning."


- Check fuel psi - a motor will 'lay down' at higher rpms when the fuel demand is the highest if the fuel pump cannot keep up. This happens a lot!
- Tune your quadrajet for this new engine if it has not been done already. Changing secondary metering rods is the easiest thing to do and may make a worthwhile change!
- When everything checks out and tuning is done - prop accordingly.

Oh, a question. I just noticed you said "It has Vortech heads and high rise intake with the quadrajet carb. "

I am not aware of a high rise quadrajet intake for the Vortech heads. What intake are you running? Are you using an adapter to mate the carb to a squarebore intake?

 

[cfm]

Ok, I re-read your posts again.

Some things to add to the list.

Find out from the engine builder what compression you have. The Vortec heads use a small combustion chamber (64cc) + you now have flat top pistons. Without knowing the particulars of the parts + machining done to your engine you could be near 10:1 compression - again assuming these are real flat tops.

Also, the Vortec heads use less total timing - typically 28-32 vs the older heads 32-36.

 

[jonate24]

I owned a 1991 Fourwinns Liberator 201 (21 foot) and it had a 300hp (crankshaft) SBC crate motor installed.

The performance you are seeing with your boat is similar to mine. I was seeing around 50mph at around 4500rpms with a 19 pitch Stiletto 3-blade.

I doubt your engine is pushing out more than 300hp with the vortec's and flat-tops. And, your hull being of the older design, is probably a little heavier than mine was.

Also don't forget that you're testing with a full tank of fuel. Those extra pounds can cost you a couple mph in top speed. I'll bet if you were running 1/8 tank of gas, you'd see about 51-52mph instead of 49mph.

One thing you can try that hasn't been mentioned in this forum is to slightly lift the engine hatch when your running the boat wide open. If you pick up RPM with the hatch slightly raised, your engine was previously being starved of air. CAUTION: DO NOT raise that hatch more than a couple of inches and raise it slowly. That wind can rip your hatch right off the boat!

 

[BCMSW]

I agree with you guys.

It is harder on a motor under full load and a one speed transmission to berunning too low of an rpm.

Plus, you are losing big horsepower! A stock small block will make max hp between 4800-5000rpm.

A typical 300hp engine will have hp numbers similar to this:

3500rpm 225hp
4000rpm 257hp
4500rpm 281hp
5000rpm 298hp

Again, this is not your engine but an example to so you the power differences at different rpms. Why count on 300hp if you are only using 250hp?

Add to this - what if your motor is losing hp do to inproper tune? More lost hp. On mild small blocks I have seen anywhere from 0-30+hp gain from 'super tuning."


- Check fuel psi - a motor will 'lay down' at higher rpms when the fuel demand is the highest if the fuel pump cannot keep up. This happens a lot!
- Tune your quadrajet for this new engine if it has not been done already. Changing secondary metering rods is the easiest thing to do and may make a worthwhile change!
- When everything checks out and tuning is done - prop accordingly.

Oh, a question. I just noticed you said "It has Vortech heads and high rise intake with the quadrajet carb. "

I am not aware of a high rise quadrajet intake for the Vortech heads. What intake are you running? Are you using an adapter to mate the carb to a squarebore intake?

Maybe it is not a high rise intake. It has higher runners than the one on the 260 that came out of it. According to the engine builder, it is the "good" Mercruiser mag intake with holes for either a quadrajet or a holley carb. I am currently running a quadrajet. It came off the 260, but he came out and tuned it on the water after the initial 10 hours of break in. Any thoughts on switching to a Holley? Would there be a performance increase? Would it be worth the price and trouble of switching over? If so, which CFM? What about a 1" spacer plate?

Camshaft is mercruiser mag cam. He checked camshaft timing when he did the valve job last summer. Pistons are flat tops. He told me to be sure to run premium fuel to avoid detonation. I always run 93 when possible.

I still need to get a gauge and some time to check the fuel pressure. Maybe I should just replace the fuel pump?

I went to 4" exhaust when I repowered so it should not have any problem breathing. I will try opening the hatch a little to be sure it is getting enough intake air.

I have an 18 Stiletto or Turbo prop that should be out of the prop shop today that I am going to try this weekend to see if I can get the rpm's up to where it is making Horsepower without losing anymore speed.

Thank you all for the great responses and ideas.

 

[cfm]

Vortec heads with the older style intake - uh, oh!

Two problems - one the bolt holes are different and two, the intake ports are much different.

A Vortec head has 4 bolt holes for the intake to head mounting. These are at 90 degrees. The pre-86 style has six bolts and are at 45 degrees. The '86-'95 style has six bolts also but the center two are at 72 degrees.

A Vortec head also has intake ports that are located higher than the older style heads.

We see many engine builders drill and tap holes in the Vortec heads so that an older style intake will fit, however, there will still be a serious port mismatch between the intake and head's intake runners. This can and does work if there are no leaks, however, hp will be less than it would be with the proper intake.

If the intake is taller than your previous one and fits both the Holley and Quadrajet then it is for the pre-Vortec motors. There are actually 2 - one is for the pre-86 and the other for the '86-'95. The only difference being the two center mounting bolt angles.


Anyway, this may or may not be your problem?

 

[BCMSW]

Vortec heads with the older style intake - uh, oh!

Two problems - one the bolt holes are different and two, the intake ports are much different.

A Vortec head has 4 bolt holes for the intake to head mounting. These are at 90 degrees. The pre-86 style has six bolts and are at 45 degrees. The '86-'95 style has six bolts also but the center two are at 72 degrees.

A Vortec head also has intake ports that are located higher than the older style heads.

We see many engine builders drill and tap holes in the Vortec heads so that an older style intake will fit, however, there will still be a serious port mismatch between the intake and head's intake runners. This can and does work if there are no leaks, however, hp will be less than it would be with the proper intake.

If the intake is taller than your previous one and fits both the Holley and Quadrajet then it is for the pre-Vortec motors. There are actually 2 - one is for the pre-86 and the other for the '86-'95. The only difference being the two center mounting bolt angles.


Anyway, this may or may not be your problem?

Thanks. I might not have vortech heads? I will have to check with him to be sure what I have. He is having some health problems (heart) right now and I have not been able to get ahold of him. I talked to his brother, who is my friend and he said he will let me know when he is doing better. Was there a name for what they used in 86-95 that I might be confusing with Vortech? I am reaching back in my memory over a year and could very well be mistaken on that part. I know it is a rebuilt Mercruiser 270 that has been "Bumped up" with rollerlifters and flat top pistons for sure. I thought he said it had the vortech heads too, but I could be wrong. Hopefully he will get better soon so I can find out. Is there a way I can tell if they are Vortech or not by looking?

 

[jonate24]

Those of us in the high performance manufacturing arena refer to the '86-'95 SBC heads as "Late Model Heads". I'm unaware of another name for these heads. Another note on SBC heads: If they are aluminum, they will always have the "early" bolt pattern. None of the aftermarket manufacturers used the "late model" bolt pattern.

 

[BCMSW]

I put on a new fuel pump today. It didn't help. Still running around 4000 rpm at 48-49 with the 19 pitch 4 blade Hill prop with another person and more gear in the boat. I also put on the 18 pitch prop I just had rehubbed, balanced, and polished. It will run 4700 rpm with the 18, but I lose about 5 mph--it only runs about 44 mph on the GPS. I planes out quicker and is very snappy. It seems to run a little hotter temperature too--closer to 160. I think I will run it a little more tomorrow, then switch back to the Michigan Wheel 19 which seemed to run the best and see what I have. I have a 1" carb spacer coming on Monday to see if that helps.

 

[Jerry G.]

Help

I have installed a 1" phenolic spacer with no ill effects. There ara a lot of varied opinions on spacers in other threads that you may want to check out. My new edelbrock intake is aluminum and will transmit more heatbthan the old cast iron Chevy that was replaced. I used to loose power in the summer so I'm giving the spacer a try. I don't know if it's affecting power. I'm waiting for a dry day to change secondary metering rods cause RPM die around 4500 Going to try that and a 20P prop if rod change has no effect.

Hope to have results soon if it ever stops raining!

Jerr G. aka Raptureman

 

[crmax]

have you tried a 19" mirage plus yet?

 

[BCMSW]

have you tried a 19" mirage plus yet?

No. I have tried a 17 Pitch mirage ran 4600 and much slower -- like 40 ish. 19 Stiletto, 19 Hill, 19 Michigan Wheel (the Mickey Mouse looking prop that does the best), and I am waiting on a 19 Ballistic. (I have also tried 23 Ballistic, 23 Powertech, 21 and 17 Stilettos, 21 Mach 4 Blade, Mercruiser QSS 17, 19, and 21, and Mercruiser 23, 21, and 19 Cleavers.) The 19 Michigan Wheel does the best so far. The 18 Stiletto or Turbo I have on today is running 44.8 MPH gps @ 4650 rpm. I ran it today until the thunderstorms drove us off the lake. I am hoping for better rpm out of the 19 when I put it back on. I am finding that there is a lot of guess work when trying to find the perfect prop since there are different rakes, cups, diameters, etc. that change rpm's more or less than 200 per inch of pitch. Ie. some 19 pitch props run better than others.