Performance Boats Forum banner

1 - 20 of 28 Posts

·
Registered
Joined
·
436 Posts
Discussion Starter #1
I have an XR outdrive so...

I want to build an engine with PEAK torque @ 6000-6300 rpm. 675-700 ft lbs.

I am looking for a very flat torque curve.


Can this be done NA with a carb? 540, 565, 572, 598?
 

·
steelcomp was here
Joined
·
26,528 Posts
I have an XR outdrive so...

I want to build an engine with PEAK torque @ 6000-6300 rpm. 675-700 ft lbs.

I am looking for a very flat torque curve.


Can this be done NA with a carb? 540, 565, 572, 598?
If you want peak tq @ that rpm, it's not going to be very user-friendly for an I/O, nor will it be very flat. You may mean peak power at that rpm. A pump gas, hyd. roller, single 4150 carb 540 will make 750hp @ that rpm and >700tq well below that, like 4700-5000 rpm.
 

·
steelcomp was here
Joined
·
26,528 Posts
If you want peak tq @ that rpm, it's not going to be very user-friendly for an I/O, nor will it be very flat. You may mean peak power at that rpm. A pump gas, hyd. roller, single 4150 carb 540 will make 750hp @ that rpm and >700tq well below that, like 4700-5000 rpm.
^add to above, the cam will depend on your exhaust and idle requirements.
 

·
Premium Member
Joined
·
1,681 Posts
You don't want the drive under torque load at max rpm.... you wont' have a drive.
 

·
Registered
Joined
·
436 Posts
Discussion Starter #5
well....i did mean torque. My thinking was that torque is what breaks the drive. seems like most break the drive while cruising at 3600-4000 rpm in peak torque.

I think that the max rpm for the drive is 6000-6300 and I would like to see close to 800 hp...so that means around 675 tq around 6000-6300 rpm. Then I thought it would help the drive live if I neutered the rest of the power band. Thats how I arrived at peak HP and Peak torque at the rpm limit.

Thoughts?
 

·
It's what we do
Joined
·
723 Posts
Max RPM should be 6000. A relatively flat torque curve is easy to achieve with a 6000 max. To achieve an HONEST 800 HP NA keeping it under 6000 and keeping the idle at 850 or below (max shift rpm), will require a minimum of 600 CI. IMO
 

·
Premium Member
Joined
·
25,975 Posts
well....i did mean torque. My thinking was that torque is what breaks the drive. seems like most break the drive while cruising at 3600-4000 rpm in peak torque.

I think that the max rpm for the drive is 6000-6300 and I would like to see close to 800 hp...so that means around 675 tq around 6000-6300 rpm. Then I thought it would help the drive live if I neutered the rest of the power band. Thats how I arrived at peak HP and Peak torque at the rpm limit.

Thoughts?
You only achieve PEAK torque is the throttle is wide open. If someone props/gears their boat to operate at 3600-4000 and the PEAK torque occurs at that RPM, then they are asking to break their drive. Like Cstraub posted, operate at PEAK torque and you won't have a drive. Moving the point that PEAK occurs at doesn't fix the problem, its still peak torque. The idea is to build an engine and gear it with PEAK torque occurring at an RPM below full throttle MAX RPM. Like Steelcomp posted, you want PEAK power to occur at or near 6000, not PEAK torque.
You are correct, an engine that makes 800HP at 6300 will be making 675 ft of torque, but that does not mean its the PEAK torque, its just the torque at 6300. PEAK could be 725 @ 4500. All depends on the CID and build.
The last thing you want is a engine that makes peak torque in the RPM range you will be operating it. That's what breaks the drives. WOT RPM should be higher than the peak torque RPM as much as possible without having the engine fall off its power curve.



100% free webcam site! | Awesome chicks and it is absolutely free! | Watch free live sex cam - easy as 1-2-3
 

·
Platinum Member
Joined
·
2,014 Posts
I have an XR outdrive so...

I want to build an engine with PEAK torque @ 6000-6300 rpm. 675-700 ft lbs.

I am looking for a very flat torque curve.


Can this be done NA with a carb? 540, 565, 572, 598?
Your drive life, will have a lot to do with your hull size, type and weight.
A 22 Daytona 2500#vs 30 v hull 6000#
 

·
Registered
Joined
·
436 Posts
Discussion Starter #9
The XR drive will live well behind a supercharged 502ci Merc 600SCI (600hp/600tq @ 5250 redline).

For more power....With a pulley change you can spin the same prop to 6000 rpm and make 800hp/666tq. The drive lives at WOT... but breaks at low rpm due to the positive displacement supercharger making more power in the entire rpm band.

This is why I feel that the XR can handle 675ft/lbs but the boat better be aired out at WOT. If the engine makes 800hp but peak torque is at 4000rpm you can't use the power.

I want 800hp @ 6300 rpm with the same power band of the 600sci 0- 5250 rpm. A 509 and a centrifugal SC would probably do the trick but I would like to know if this can be done with a simple carbed 565ci?
 

·
Platinum Member
Joined
·
2,014 Posts
The XR drive will live well behind a supercharged 502ci Merc 600SCI (600hp/600tq @ 5250 redline).

For more power....With a pulley change you can spin the same prop to 6000 rpm and make 800hp/666tq. The drive lives at WOT... but breaks at low rpm due to the positive displacement supercharger making more power in the entire rpm band.

This is why I feel that the XR can handle 675ft/lbs but the boat better be aired out at WOT. If the engine makes 800hp but peak torque is at 4000rpm you can't use the power.

I want 800hp @ 6300 rpm with the same power band of the 600sci 0- 5250 rpm. A 509 and a centrifugal SC would probably do the trick but I would like to know if this can be done with a simple carbed 565ci?

I like the XR drive we have run several of them,
best suited for the 496HO and 525 package

Limited the 572 motors to 650 hp ea in twins for life

And a spare on the stern jack.

Hp and #6 drives final answer
 

·
Registered
Joined
·
436 Posts
Discussion Starter #11
I like the XR drive we have run several of them,
best suited for the 496HO and 525 package

Limited the 572 motors to 650 hp ea in twins for life

And a spare on the stern jack.

Hp and #6 drives final answer
ok. you limited the 572 to 650....at what rpm did it make 650? did you prop to that rpm?
 

·
steelcomp was here
Joined
·
26,528 Posts
The XR drive will live well behind a supercharged 502ci Merc 600SCI (600hp/600tq @ 5250 redline).

For more power....With a pulley change you can spin the same prop to 6000 rpm and make 800hp/666tq. The drive lives at WOT... but breaks at low rpm due to the positive displacement supercharger making more power in the entire rpm band.

This is why I feel that the XR can handle 675ft/lbs but the boat better be aired out at WOT. If the engine makes 800hp but peak torque is at 4000rpm you can't use the power.

I want 800hp @ 6300 rpm with the same power band of the 600sci 0- 5250 rpm. A 509 and a centrifugal SC would probably do the trick but I would like to know if this can be done with a simple carbed 565ci?
The power curve of an NA engine that made a peak tq of 660lbs/ft @ 6000 rpm will be useless below that rpm. You'd never get on plane and the cam would have the idle characteristics of a Pro Stock engine.
 

·
Platinum Member
Joined
·
2,014 Posts
ok. you limited the 572 to 650....at what rpm did it make 650? did you prop to that rpm?
30 Daytona
1.36 gear 34-36 pitch props
shifter friendly and stump pulling power on demand

Like, I said earlier the XR is a nice drive
that said. It is the weak link in the chain

A light boat you can get away with much more
using good driver skills on power applications
for drive life
 

·
Premium Member
Joined
·
25,975 Posts
The XR drive will live well behind a supercharged 502ci Merc 600SCI (600hp/600tq @ 5250 redline).

For more power....With a pulley change you can spin the same prop to 6000 rpm and make 800hp/666tq. The drive lives at WOT... but breaks at low rpm due to the positive displacement supercharger making more power in the entire rpm band.

This is why I feel that the XR can handle 675ft/lbs but the boat better be aired out at WOT. If the engine makes 800hp but peak torque is at 4000rpm you can't use the power.

I want 800hp @ 6300 rpm with the same power band of the 600sci 0- 5250 rpm. A 509 and a centrifugal SC would probably do the trick but I would like to know if this can be done with a simple carbed 565ci?
IF the drive can live with 800HP at 6300, it can live at 4000, even if the peak torque is at 4000. You just can't hammer it at 4000. You have to drive past that at part throttle. No engine, blown or NA makes peak torque at less than WOT.

Any engine that has the SAME power band as a 600sci is EXACTLY THAT, the SAME power band. The SAME torque at the SAME RPM. A 509 with a centrif would NOT have the SAME band, it would have less torque at lower RPM. That's not the SAME power band.
I think you mean the same PEAK power. You seem to have your power band and peaks a little confused.



100% free webcam site! | Awesome chicks and it is absolutely free! | Watch free live sex cam - easy as 1-2-3
 

·
Registered
Joined
·
436 Posts
Discussion Starter #15
thanks everyone for your help....I think I get it now. peak tq @6300 runs like shit in lower rpms....peak HP @ 6300 makes a lot of torque but you control that with throttle...if the boat is not too heavy the drive may live.

Steelcomp....I saw the 565 you built for the chevelle in the other thread...what power can be had with a 565 in a boat?
 

·
steelcomp was here
Joined
·
26,528 Posts
thanks everyone for your help....I think I get it now. peak tq @6300 runs like shit in lower rpms....peak HP @ 6300 makes a lot of torque but you control that with throttle...if the boat is not too heavy the drive may live.

Steelcomp....I saw the 565 you built for the chevelle in the other thread...what power can be had with a 565 in a boat?
Now you're getting it.:thumb: Very rarely will your drive ever see peak tq for more than a split second as you accelerate through it. You can't stay at full throttle, peak tq. unless you're towing something awfully heavy and then I'd guess you'd blow through the prop.

A comprehensively built NA, pump gas, one carb 565 should be able to make an honest 750+hp @ ~6000 rpm with an I/O-friendly cam. A few years ago I did the top end for a pump gas 540 that made 909hp @ 6300, 823 tq @ 5300. That had a TR and a pair of 750's. The cam on that probably wouldn't be very I/O friendly though. ;)
 

·
steelcomp was here
Joined
·
26,528 Posts
thanks everyone for your help....I think I get it now. peak tq @6300 runs like shit in lower rpms....peak HP @ 6300 makes a lot of torque but you control that with throttle...if the boat is not too heavy the drive may live.

Steelcomp....I saw the 565 you built for the chevelle in the other thread...what power can be had with a 565 in a boat?
Also wanted to mention...you notice how Mercury rates their engine's rpm ranges at FULL THROTTLE. In other words, don't use full throttle unless you're in that rpm range. They're trying to tell you something. ;)
 

·
Platinum Member
Joined
·
2,014 Posts
Also wanted to mention...you notice how Mercury rates their engine's rpm ranges at FULL THROTTLE. In other words, don't use full throttle unless you're in that rpm range. They're trying to tell you something. ;)
"Words of wisdom"

Seriously, if you want to play, rather than baby.
Upgrade your drive system.
The better drives also have better performance prop selection

Better to sell a complete working XR
than a basket of broken parts
 

·
steelcomp was here
Joined
·
26,528 Posts
"Words of wisdom"

Seriously, if you want to play, rather than baby.
Upgrade your drive system.
The better drives also have better performance prop selection

Better to sell a complete working XR
than a basket of broken parts
This is the true solution to the problem.:))THumbsUp
 

·
Registered
Joined
·
436 Posts
Discussion Starter #20
"Words of wisdom"

Seriously, if you want to play, rather than baby.
Upgrade your drive system.
The better drives also have better performance prop selection

Better to sell a complete working XR
than a basket of broken parts
Like what??? already upgraded the XR but the gears always remain the same. I have heard some good things aout the IMCO SCX...any idea where it breaks?
 
1 - 20 of 28 Posts
Top