Volvo D6 DPR drive/HuntonXRS37

peter unwin

Senior member
Joined
Sep 1, 2006
Messages
557
Location
East Mids
Cruising area
Southampton
Boat name
Cheetah
Boat make
XRS37 hunton
Engines(s)
twin volvo D6's
Here is a brief summary of the work done on the Volvo D6 DPR drives;

At the beginning of March 2007 I took delivery of a new Hunton XRS37 powerboat equipped with Volvo D6 DPR drives with GR8 props. Out of the box once it had been run in, it ran at 52 knots but the boat would not respond to trim and ran very wet. So I started prop modification and testing with Steel developments , our 1st attempt resulted in a 3 knot gain, our 2nd attempt gave us another 2 knots as we were able to use more trim and reduce the wetted area. Since we were running at maximum engine RPM and increasing our speed through less slip and more efficient props we changed to GR9 's which in standard form gave us 52 knots , so again we went thru stages 1 & 2 with Steel Developments which gave us 58knots and it was beginning to lug the engines down so we really needed more power....

Another problem we found with the extra speed was that when the boat came out of the water at max velocity the rubber exhaust bellows failed . This problem was cured by fabricating a new set of free flow risers and straight through transom exhausts.

So in our search for more power we contacted DMS at Southampton and after much discussion with DMS, Rob wrote us a new ECU program for the Volvo engines, they were reprogrammed to give us more top end power without increasing the low end torque and stressing the drives too much.

As soon as testing resumed it became apparent that the standard cooling system could not cope with the increase in power . so the 1st mod that we did was to manufacture 20% smaller water pump pulleys and correspondingly shorter drive belts which surprisingly made very little difference. On further investigation it was noticed that the water pickup holes in the nose cone of the drive legs was far too small and torturous to flow the volume of water the engines required. So we opened up this hole and improved the water flow into the pickup. We now have more than enough water to control the engine and charge cooler temperatures.

So with the modded GR9 props , the Engine ECU reprogramming , the free flowing exhaust system and the improved cooling we can now run at 62 knots. but we have run out of pitch on the GR9 props so here is the plan for early 2008.

1. Do a 3rd stage mod on the GR9 props.
2. Fit a 10FT x 10" wide flat planing area on the bottom of the hull.
3. Fit pointed nose cones on the DPR drive and move water pickups to the bottom of the flat planing area

We are hoping for 64-65 knots

More technical information can be made available once all the trials have been completed

The testing and development along with a bit of pleasure cruising has added 300 engine hrs since March 2007.

I will add some pictures soon.
 
engines

are they the 310 or 350 D6 s
 
Great project!

Good to see someone working to improve stuff in this way, it doesn't happen often these days, as everyone is always so worried about warantee.

Please keep us informed.
 
Another problem we found with the extra speed was that when the boat came out of the water at max velocity the rubber exhaust bellows failed . This problem was cured by fabricating a new set of free flow risers and straight through transom exhausts.
Interesting. Other than removing the bellows problem, did you find any performace change after doing this?

I'd also be interested to know about the stage 1 and 2 modifications to your props and what the stage three mod is likely to entail.
 
With that sort of speed you should be entering this boat in the Cruiser Class of the RB08 against the other Huntons. That should give Jeff a bit of a surprise!
ML.
 
With that sort of speed you should be entering this boat in the Cruiser Class of the RB08 against the other Huntons. That should give Jeff a bit of a surprise!
ML.


I here Jeff 43 could be abit of a surprise.
 
Interesting. Other than removing the bellows problem, did you find any performace change after doing this?

I'd also be interested to know about the stage 1 and 2 modifications to your props and what the stage three mod is likely to entail.
Firstly the through transom exhausts made we think around 20hp per engine gain,a huge difference to the bottom and torque, to the point where the super chargers are not really required as the turbos spool up so early.

Stage 1 on the propellors was equalised pitch between blades,thin blades where possible,sharpen edges & apply more cupping plus balance.

Stage 2 on propellors was more cupping still.

Stage 3 on propellors actuallly increasing pitch to reduce engine rpm.
 
Peter, thanks for that. One more question; was the increase in performance, due to rerouting the exhaust, noticeable before you had the fuelling remapped?
I'll not bore you with the details but I had come to the conclusion that exhaust back pressure was also a problem on my KAD300 as is slow spooling up of the turbo. I've had a modification made to the turbo which may interest you. Volvo turbos suffer from rusting in the exhaust turbine housing and they are made with clearances to cope with that. I've had a stainless insert fitted into the housing so the clearances are now tightened up to give better drive and also a slightly larger compressor wheel is fitted to get over a dip in the inlet pressure at around 3000rpm. I've done prop mods too but the results were inconclusive because of the turbo problem.

Testing is planned for tomorrow. :)
 

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Peter, thanks for that. One more question; was the increase in performance, due to rerouting the exhaust, noticeable before you had the fuelling remapped?
I'll not bore you with the details but I had come to the conclusion that exhaust back pressure was also a problem on my KAD300 as is slow spooling up of the turbo. I've had a modification made to the turbo which may interest you. Volvo turbos suffer from rusting in the exhaust turbine housing and they are made with clearances to cope with that. I've had a stainless insert fitted into the housing so the clearances are now tightened up to give better drive and also a slightly larger compressor wheel is fitted to get over a dip in the inlet pressure at around 3000rpm. I've done prop mods too but the results were inconclusive because of the turbo problem.

Testing is planned for tomorrow. :)
Yes that was before the remap, after the remap engine hp rose to circa 420 still with no smoke. So a further remap is in the ofing for even more power.
 
Yes that was before the remap, after the remap engine hp rose to circa 420 still with no smoke. So a further remap is in the ofing for even more power.
Thanks for that. It's a good increase in power from little modification. As you are probably aware, Volvo produce a 435hp D6; but they wont sell it to you with a DPR drive.

You might be starting to live dangerously. :)
 
Pictures of Hunton XRS37 .

Here are a selection of pictures of the modifications to the boat. the pictures of the risers were taken before we had them ceramic coated, which reduces the heat loss from the hot area of the riser...
 

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Cool. Peter, are they noisy?
 
Hi JW,
the 435 D6 has a larger turbo housing and charge cooler pipework and won't fit the transom shield of the DPR drive without spacing it off and moving the engine forward, we think that Volvo have built in a reasonable margin of safety into the drive and as it is a relatively light boat we think that the drive can cope, of course only time will tell , we have done over 200 hours in standard form + 100 hours after the mods so far.. we are also changing the oil in the drive every 50 hours and checking for debris each time. Another interesting factor to bear in mind that the boat is usually either idling/burbling up and down channels or flat out, it doesn't do alot of cruising ...
 
Hi,
there is a small amount of turbo whine at low revs but once the boost pressure builds the turbo along with the water acts as a silencer, so all in all its pretty refined really.
 
Thanks. I may be following your route shortly. I really feel the engine is stifled at lower revs and the boost pressure never gets above 20psi. Volvo always seem to use a water bypass from the exhaust elbow and my understanding is that this is done to prevent excess steam creating backpressure when it is heated by exhaust gas. That implies the standard exhaust is known to be limiting. As a wee experiment, I blocked off the bypass and the exaust downpipe reduced in temp by about 12° but it killed the performance in the 2000-3000rpm range. The boat barely got onto the plane when it was loaded with a few folk! See this thread.
 
..the 435 D6 has a larger turbo housing and charge cooler pipework and won't fit the transom shield of the DPR drive without spacing it off and moving the engine forward...
I wasn't aware of that, it's useful info to know.
 
Hi All,
Cheetah is now approaching 1000 hours of very spirited use... and the engines are begining to show signs of wear and tear from the abuse that they have received so they are soon to be removed for a refresh. At the same time i will extract as much power as we can squeeze out of them, i will also install the fly by wire steering system as this boat will be used for demonstration purposes.

Mechanical Modifications To Include:
1. Hybrid turbos to flow much more air.
2. Much larger charge coolers.
3. Injectors from the 435 engine.
4. Heat exchanger from the 435 engine.
5. Billet aluminium crankshaft pulley.
6. Much larger diameter through transom exhausts.
7. Remap of engine ECU to increase both power and rpm.
8. Dry sump the DPR drives in an effort to make them live with the increased power.

Peter
 
Hi All,
Started the preparations to remove Cheetah's engines on Thursday, to speed up the conversion process first job was to remove the injectors unfortunately what should have been a couple of hours to get the injectors out turned into a bit of a marathon as water had penetrated the engine cover and got into the injector pockets, however i persevered and managed to remove ten of them looks like i am going to have to make an extractor to recover the other two so my plan to have them modified to the 435 spec while we are in America is not going to happen they will have to wait till i get back, also brought the props back to work so that i can reduce the blade area on the front prop and pitch the front and rear props up to absorb the extra power. The sample wing profiles have also arrived so there is plenty to be going at when we get back from our holidays.

Peter
 

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