GM HT383 Repower

[pachanga27]

In a separate thread - it was mentioned the GM HT383 as a repower option for the Mercruiser 350.

My question - that 383 - rated at 340 HP at 4500 RPM - I would believe that is the HP at the crank rating - would there be enough HP loss that by the time it got to an Alpha drive - would the losses be enough that the Alpha could survive at 4400 RPM? (WOT) According to the RPM/HP chart - the 383 is at 300 HP at 4000 RPM. If I were to be aware of not holeshotting WOT - then I might be able to get an Alpha to live with that kind of power. Another question - in my case - I have a 1989 27ft Sea Ray with twin 350s with Alphas. At the time in 1989 - those engines were rated at 260 HP. 24 years later - obvisously they are not putting out that HP anymore - even though they still run damn good and i really have no complaints ... but of course I would love to have more HP --- at a cost of course.. but that is just always the case. Want to play - you gotta pay. So - in the end - safe move or not worth it for an old boat? Were the 1989 Alphas made well? Mine appear to be pretty solid even after all these years - the hour meters are 750 hours. Is there a lesser torque load on the outdrives when two are pushing the boat verse one engine/oudrive?

 

[Walt T]

Re: GM HT383 Repower

I understand the Alpha 1 is rated at 300 hp. I've also seen big blocks driving them. They are not racing drives. You really might consider an SEI drive, they're supposedly warrantied to 400 hp. If you just want your nice boat to go a little faster and plane a little quicker the Alphas will probably hold up but I'd baby it. You're pretty much getting the best performance you're gonna get unless you go to Bravo 3's. Dropping 383 strokers in there might help a little bit or you may not even notice a difference because that is a big heavy boat. The best scenario obviously is twin 454's and Bravo 3s but the twin 350's are pretty darn good. I think you will be disappointed in the money spent vs advantaged gained by going to twin 383s. But then if you're going to rebuild engines anyway well you may as well. If you're gonna tear out perfectly good motors and replace them, You'll regret spending that much money. Using props, trim, trim tabs you should get the best performance and top speed you're ever going to get from that. It'll take 200hp+ to push it 5 mph faster. So dig deep and go buy a 33' Fountain autographed by Ol' Reggie hisself and tear up the lake with those triple blown 502s and surface drives. Be beating off the babes with an oar. Well, wifey will anyway.

 

[Bondo]

Re: GM HT383 Repower

In a separate thread - it was mentioned the GM HT383 as a repower option for the Mercruiser 350.

My question - that 383 - rated at 340 HP at 4500 RPM - I would believe that is the HP at the crank rating - would there be enough HP loss that by the time it got to an Alpha drive - would the losses be enough that the Alpha could survive at 4400 RPM? (WOT) According to the RPM/HP chart - the 383 is at 300 HP at 4000 RPM. If I were to be aware of not holeshotting WOT - then I might be able to get an Alpha to live with that kind of power. Another question - in my case - I have a 1989 27ft Sea Ray with twin 350s with Alphas. At the time in 1989 - those engines were rated at 260 HP. 24 years later - obvisously they are not putting out that HP anymore - even though they still run damn good and i really have no complaints ... but of course I would love to have more HP --- at a cost of course.. but that is just always the case. Want to play - you gotta pay. So - in the end - safe move or not worth it for an old boat? Were the 1989 Alphas made well? Mine appear to be pretty solid even after all these years - the hour meters are 750 hours. Is there a lesser torque load on the outdrives when two are pushing the boat verse one engine/oudrive?

Ayuh,.... Are ya boatin' in sweetwater, or brine,..??

Raw water cooled, or freshwater cooled,..??

I ask, 'cause the HT383s are aluminum headed motors,....

 

[pachanga27]

Re: GM HT383 Repower

Walt T
Thanks for the reply - I was mostly thinking about when the time comes to replace the current 350s... which might be 10 years or might be next year. I really don't think next year - the motors are 750 hours each but are running strong and excellent still. Put 65 hours on them this past spring and summer and no problems. But - when I do... I really think that the HT383 would be an excellent choice as long as I use the extra horses in the proper manner.. I am very pleased with the way the boats comes on plane - quickly and cruises at 42 to 46mph The boat is heavy... 1989 heavy. I figure with a full tank of gas - 160 gallons, the wife and I... supplies, gear, etc...it is probably at 6500 pounds. I was hoping I might a little more quicker acceleration from 30mph to 50mph than I get now. I usually am running at 3800 to 4000 RPMs and that way if I need to move a little faster to avoid traffic I have room to throttle up to 50 to 55mph. and BTW... boy would I love to have a Fountain with two big ol' honkin' motors. Problem is that the motors in those boats cost more than my boat and motors together.

 

[pachanga27]

Re: GM HT383 Repower

Ayuh,.... Are ya boatin' in sweetwater, or brine,..??

Raw water cooled, or freshwater cooled,..??

I ask, 'cause the HT383s are aluminum headed motors,....

Bondo...

Freshwater only... as much as I would love to go to Charleston, SC and travel the intracoastal waterway.... but this boat is freshwater only.

freshwater cooled - I change the impeller in both outdrives once every two years regardless... (I know .. overkill)

but speaking of the aluminum heads...... any idea of weight savings when comparing the 1989 350s compared to the new HT383s?

 

[Bondo]

Re: GM HT383 Repower

Bondo...

Freshwater only... as much as I would love to go to Charleston, SC and travel the intracoastal waterway.... but this boat is freshwater only.

freshwater cooled - I change the impeller in both outdrives once every two years regardless... (I know .. overkill)

but speaking of the aluminum heads...... any idea of weight savings when comparing the 1989 350s compared to the new HT383s?

Ayuh,.... Ya mean raw water cooled, right from the freshwater pond,.....

Freshwater cooled is with antifreeze, 'n an exchanger,...

I donno the weight differences, but a quick google outa find out,...

The Alphas will be the weak link, but with proper maintenance, 'n bein' Easy on 'em, they'll live very long lives,...

 

[pachanga27]

Re: GM HT383 Repower

Ayuh,.... Ya mean raw water cooled, right from the freshwater pond,.....

Freshwater cooled is with antifreeze, 'n an exchanger,...

I donno the weight differences, but a quick google outa find out,...

The Alphas will be the weak link, but with proper maintenance, 'n bein' Easy on 'em, they'll live very long lives,...

my mistake no doubt .. raw water cooled.
thanks ..

 

[Silly Seville]

Re: GM HT383 Repower

Torque gets you moving...horsepower keeps you moving.
Torque is what destroys the Alpha gear sets, not horsepower. A gentle right hand is appropriate.

SEI website says "300 horsepower rating on SE106 and SE116 drives".

A pair of aluminum heads shave off 40 lbs. over their iron counterparts.

 

[HT32BSX115]

Re: GM HT383 Repower

Dropping 383 strokers in there might help a little bit or you may not even notice a difference because that is a big heavy boat. The best scenario obviously is twin 454's and Bravo 3s but the twin 350's are pretty darn good. I think you will be disappointed in the money spent vs advantaged gained by going to twin 383s.

I would agree with that. going from an Alpha to a Bravo III would not only give you more than enough power handling but it would also make the performance really shine!

(bring money though!!)


Cheers,


Rick

 

[Walt T]

Re: GM HT383 Repower

I think your speed estimates are optimistic. But no matter. We all agree the drives should be fine and I'd definitely install 383s if I were pulling the engines anyway. I wouldn't use the HT's, I'd build my own strokers but I'm capable of doing that. Not everyone is a mechanic here. By the way saving 40 lbs on heads and gaining 75 hp or so will make zero difference in a boat that size. I've seen it over and over, well meaning smart guys thinking a cam and intake manifold will get their boat screaming forgetting how much resistance there is in the water. A deep V hull intended for smooth cruising has to ride deeper in the water at cruise to achieve that nice ride even in chop. That is a huge amount of water to push aside and at 8 lbs a gallon it's like towing a house with a 75 mph headwind. Then, going faster makes the power requirement skyrocket for just 5 mph. Here's a better way to think of something like this:
An engine producing more HP at the same RPM as a different engine will require less throttle opening to do the same amount of work and therefore is not working as hard. This equates to better fuel economy. Not much though, you'd probably only notice it if you had a fuel meter counting every gallon and accurate GPS speed. Now, this is at normal cruising speed. The engine produces more power than the stock engine but going to WOT makes no difference because the HP required to go faster in a boat skyrockets for just a few mph. As I said, it will take 200+ HP to get your big ol yacht to go just 5 mph at top speed. You'd have to install blowers on top of big blocks and then B 3's to handle it to get there.

I was talking triple 502's on that Fountain no way would I be caught dead in a silly twin engine Fountain

 

[pachanga27]

Re: GM HT383 Repower

I think your speed estimates are optimistic. But no matter. We all agree the drives should be fine and I'd definitely install 383s if I were pulling the engines anyway. I wouldn't use the HT's, I'd build my own strokers but I'm capable of doing that. Not everyone is a mechanic here. By the way saving 40 lbs on heads and gaining 75 hp or so will make zero difference in a boat that size. I've seen it over and over, well meaning smart guys thinking a cam and intake manifold will get their boat screaming forgetting how much resistance there is in the water. A deep V hull intended for smooth cruising has to ride deeper in the water at cruise to achieve that nice ride even in chop. That is a huge amount of water to push aside and at 8 lbs a gallon it's like towing a house with a 75 mph headwind. Then, going faster makes the power requirement skyrocket for just 5 mph. Here's a better way to think of something like this:
An engine producing more HP at the same RPM as a different engine will require less throttle opening to do the same amount of work and therefore is not working as hard. This equates to better fuel economy. Not much though, you'd probably only notice it if you had a fuel meter counting every gallon and accurate GPS speed. Now, this is at normal cruising speed. The engine produces more power than the stock engine but going to WOT makes no difference because the HP required to go faster in a boat skyrockets for just a few mph. As I said, it will take 200+ HP to get your big ol yacht to go just 5 mph at top speed. You'd have to install blowers on top of big blocks and then B 3's to handle it to get there.

I was talking triple 502's on that Fountain no way would I be caught dead in a silly twin engine Fountain

Walt..

yes... speeds were very optimistic. Sometimes I get caught up with the possibilities.

After reading your reply - I am educated. I know it takes more than just losing a few pound here and there to make the use of only a small amount of additional HP... especially in an old Pachanga. But.. reality is that the HT383s will not give me that kick in the butt performance I was thinking it might. I suppose the best case with the HT383s would be.... I open the hatch and see two shiny new engines ....

 

[Scott Danforth]

Re: GM HT383 Repower

visit scream and fly or offshore only, and there are plenty of people putting 383's and 406's in front of Alphas.

RLC performance even makes a modified Alpha for behind 600+ HP motors RLCPerformance.com

However with only 750 hours, I dont think your engines are as tired as you believe. If it were me, I would check compression, then pull the heads and take a look.

with a cam and head change, you can get to over 300hp with your existing motors. Although a pair of healthy 383's pushing 450hp would be nice as well.

I posted stock GM cam numbers in my thread here http://forums.iboats.com/volvo-pent...-into-performance-upgrades-aq271c-503800.html Note that there is a bit of improvement to be had.

 

[Walt T]

Re: GM HT383 Repower

You ever try pulling heads in the engine bay of a 27 foot Sea Ray twin 350 set up?

 

[Scott Danforth]

Re: GM HT383 Repower

You ever try pulling heads in the engine bay of a 27 foot Sea Ray twin 350 set up?

No, but I helped pull the motors of a 27' Carver with twin 350's. once the motors are out, pulling them apart is easy

 

[Tail_Gunner]

Re: GM HT383 Repower

Power: 340 HP @ 4500 RPM,..................... 435 ft. lbs. of torque @ 4000 RPM................The pony's wont kill the drive but that torque will. Keep in mind you have two drive's not one making launching much less stressful.. The typical gm 350 has about 320lbs ft of torque...420 is BB territory...I popped a alpha one gen one with a 454 hit a rock not even enough damage to the prop to notice at first..but that strike just sheard the lower shaft and snapped the gearing in the lower unit. Using SEI drive now and it's holding up so far..finger's crossed.

 

[pachanga27]

Re: GM HT383 Repower

No, but I helped pull the motors of a 27' Carver with twin 350's. once the motors are out, pulling them apart is easy

I can tell you that replacing the starter on the starboard motor is about as fun as ...well.... nothing. It was not fun. Period.

However - truthfully - the engine bay of the Pachanga 27 is not bad at all to work on the 350s. Plenty of room to move around in and over the motors.

 

[pachanga27]

Re: GM HT383 Repower

Power: 340 HP @ 4500 RPM,..................... 435 ft. lbs. of torque @ 4000 RPM................The pony's wont kill the drive but that torque will. Keep in mind you have two drive's not one making launching much less stressful.. The typical gm 350 has about 320lbs ft of torque...420 is BB territory...I popped a alpha one gen one with a 454 hit a rock not even enough damage to the prop to notice at first..but that strike just sheard the lower shaft and snapped the gearing in the lower unit. Using SEI drive now and it's holding up so far..finger's crossed.

That was my thinking.. .that with two outdrives launching the boat to plane - the stress load would be within the stress limits of the outdrives if I just did not hammer the throttles. As in, I do not firewall them now -just progressively feed the power and the Pachanga comes up on plane very nice and quick. I really can't complain about the performance of the Pachange 27. I just thought when it came to re-power - the HT383s would be a very attractive price point option. On Lake Murray in SC -high speed is not the smart way to make friends with the other boaters, fishing folks and the DNR folks.

 

[Tail_Gunner]

Re: GM HT383 Repower

Agreed the 383 would be my choice and sei drives are a dime a dozen....