Hot Rodding 8v71TIs?

[stormchaser]

Not that I'm seriously considering it due to shorter engine life...but were there any higher HP versions of the 8v71TIs? I mean higher than my 425/435s? If so, what was the difference and would it be possible to up the output of standard ones? Like sets say someone wanted more power and didn't care as much about super long life. Lets say you were okay with getting 1,000-1,500 hours before majors...how much power could you reasonably get out of them? Thoughts?

 

[Boatsb]

I have heard of them at 460 or maybe 485 but that is pushing it.\\

 

[Pete]

DD offered a 671 at 485 HP with a life around 1000 hours, so I would speculate that somewhere in the low 600's would be possible.

Pete

 

[Red Hatt]

I was told by a mech. that you could change the turbo size and put in larger injectors and get 550 H.P out of a 8 71 ti. How long the engine would last he didn't say, but he did say it was almost like having a 8 92 ti.

 

[stormchaser]

Man, if it didn't totally wreck longevity, I'd love to get 500ish hp out of them to regain lost speed due to live aboard weight, but I'm also not willing to do anything that will hurt her or hurt her resale value.

 

[SKYCHENEY]

I've never see an 8v71ti at over 435hp. If there are any, then it must not have worked out too well or there would be more of them. I'm sure many owners feel the same as you do Dave.

Now the 6v92TA's that were put in the later 53's could be pushed up from the 465-485hp range to 550hp. But, again, this is not too common as the cost of new wet turbo and manifolds is just not worth the gains.

You'd be better off reducing weight and/or trying to get the best props for your application. You may also not be getting full hp out of what you have. If they're tired, maybe a tune-up would help. It might be worth a service call just to see.

 

[stormchaser]

Yeah, first thing is props. I know I'm over propped by a couple hundred rpms (150-200 depending on which tachs you believe). So in the spring the wheels will come off and go to Black Dog Props for the PropScan tuning and I will have them tuned to the highest degree possible for accuracy. I figure itd well worth the outlay as you dont have to do it often and it can make a big difference in speed and efficiency. My previous boat picked up about 10% in speed at the same cruise RPM or 12% reduction in fuel at the same speed. I can only hope for such results here...reducing weight is unlikely, at least not by much...maybe I could get the whaler down from the top, but I doubt a few hundred pounds will make much difference...

 

[Red Hatt]

Ron Dorr with Diesel Plus in fl. is the Mech. that told me about Upping the the H.P. on the 8 71 Ti.

 

[saltshaker]

535HP is common on 8V71TI's with a bypass blower. I've seen a few 46 Bertrams and 46 Hatts that had them. I had a chance to buy a pair out of a 46 Hatt. 700 hours since they were modified and they were shot. Everything I've heard about this "upgrade" says don't do it. Never saw a boat with them that made it past 1000 hours.

 

[stormchaser]

I'm actually surprised the self destruct that fast. That's still less than 1hp per cubic inch. I would think up to 500ish hp would be fairly safe. I certainly don't want engines that die every 700 hours...heck even 1000 seems very short, although that would be nearly 10 years for me at this rate.

 

[SKYCHENEY]

There is one more thing that can be done. I've heard of it, but not seen it. There is supposedly a 56MY and a 53MY that have both had transmissions changed to 3:1 reduction. Same engines/same hp, but with the slower prop speed, they also switched to 5 bladed props. Bigger shafts may also be necessary to achieve this. The reported increase in efficiency is somewhere around 20%. It's hard to believe, but it would make your boat similar to the Hatteras propulsion systems of today.

I personally know of a HOF member that is looking into this right now for his 53(not me, at least until I see one that has been completed and with good results).

 

[REBrueckner]

Precision Marine in New Rochelle where I kept my Hatt boosted the performance of 8V71TI's in a 1973 46 Bertram SF. After the work the owner told me he got another 2 knots which he was looking for. Greg Cirillio, the owner of Precision, advised me not to do it do to reduced engine life. Don't know how it all worked out as the boat now fishes from Montaulk.

 

[saltshaker]

Before I bought my Hatt, I looked at a 46 Bertram with the modified 8V71's. I was told the engines failed within weeks of the mod. They made some changes and she went another 100hrs and blew one engine. When I looked at the boat she was de-tuned to somewhere around 475-500hp but no one was sure exactly what they were. Engines had 400 hours on them at that point. Needless to say I didn't even consider an offer on that one.

I know Mako Marine in Freeport, NY did a 46 Hatt years ago. Engines only had a few hundred hours on them when the owner decided to do a complete refit including repower. In the end the engines were sent to Atlantic Detroit Diesel for a complete overhaul.

 

[saltshaker]

There is one more thing that can be done. I've heard of it, but not seen it. There is supposedly a 56MY and a 53MY that have both had transmissions changed to 3:1 reduction. Same engines/same hp, but with the slower prop speed, they also switched to 5 bladed props. Bigger shafts may also be necessary to achieve this. The reported increase in efficiency is somewhere around 20%. It's hard to believe, but it would make your boat similar to the Hatteras propulsion systems of today.

I personally know of a HOF member that is looking into this right now for his 53(not me, at least until I see one that has been completed and with good results).

Tom Slane had a 53C that someone was trying to do that to. They pulled the shafts and one gear but never finished the job. Seems like an insane amount of work and expense. Hard to believe it would make much of a difference but a big slow turning prop is more efficient than a small fast one.

 

[GJH]

Dave, is Black Dog local up there ? I had my props done at Miller Island and was very happy with the results. The yard I use in Baltimore swears by them.

George
Headed down the Neuse River to Ocracoke doing 8.7 knots..
Reflecting that almost every Hatt made has passed this way before..

 

[stormchaser]

It's a couple hour drive, but they are well worth it. They did fantastic work on my trawlers prop, it made a BIG difference....

Based on what I'm reading here, it sounds like 425/435 is just right for these engines. I wish I could SAFELY and somewhat easily get 475, but it seems like that is not the case. So, I will do what I can with what I've got...

 

[Nonchalant1]

Don't forget HORSEPOWER = HEAT.

The engines would need new raw water pumps and new bigger heat exchangers, etc.

Doug

 

[Pascal]

buying a 53MY for speed is the wrong decision... if you want speed, you bought the wrong boat. it's like... let see... those folks who voted for you know who a year ago...

 

[Glory]

I was told by a mech. that you could change the turbo size and put in larger injectors and get 550 H.P out of a 8 71 ti. How long the engine would last he didn't say, but he did say it was almost like having a 8 92 ti.

With out changing the blower drive gear ratio larger injectors will do little with out more air. The 485HP 6-71 and all of the 92s, 635 6V92 and 735 8V92 use a by pass valve, ( that is the "B" in TIB) to get around the blower when the turbo builds pressure past the blover's ability to deliver air.

This was never engineered in to the 8v71. There is however a blower gear set that will take you to a HP setting in the mid 500 HP area. It is my understanding this was developed for the millitary.

JM

 

[stormchaser]

interesting. Coming from an automotive forced induction background, I've always wondered wjy have a supercharger AND twin turbos. Why not just use a larger sc? Or ame sc w a different gear ratio?