| Author |
Message |
    
David Jones
New member
Username: dunn_dee
Post Number: 1
Registered: 07-2007
| | Posted on Wednesday, May 14, 2008 - 05:09 am: | 
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G'day fellas, This is my first post and I'd like to say that you guys make this a great informative site.
Iam in OZ and have a 3.0lt 95 mercruiser in a 19.5 deep v boat with 510hrs.
We have done a fair bit of maintenence on the old girl, but I have been fishing around for different re-power options.
I came across the GM Marine web site and among the other Base marine line up that I know mercruiser use, I noticed a new 2.4lt DOHC 4cl with variable valve timing. It is also currently used in some of their cars.
It looks like it pumps out about 175hp -( no doubt at the motor not prop) and with very similar tourque to the 3.0lt, The length dimensions are really close to that of the 3.0lt
There is also a company in New Zealand that already offer this motor with a 'marinising kit' wich looks to be every thing except for a flame arrestor. - Thing is they were semi-race engines and produce around 195hp.- I'd like a bit more than 135hp, but I want continous, reliable power.
Without starting a car motor in boat dispute ( I fully understand the resasons for that ) I have a few questions
1. Does any one Know any =thing about this motor?
2. As it is V.V.Timing, would that eliminate the need for marine cams if it's not already equipped?
3. If I did throw one in the boat and had say 160-170 prop hp , Should I expect a decent increase in cruising speed ( 10mph)??
I know it's a bit off the normal posts, but the kind of input I see on this site could rally help.
Dave. |
Troy
Advanced Member
Username: troym
Post Number: 507
Registered: 09-2004
| | Posted on Wednesday, May 14, 2008 - 05:29 am: |
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How fast are you cruising now?
What size & pitch prop are you using now?
Would be nice to know what we're starting with.
Understanding you want more, but that 3.0L you have now is probably one of the best along the lines of "continuous, reliable power". |
Rod Stewart
Senior Member
Username: rod_stewart
Post Number: 1309
Registered: 08-2006
| | Posted on Wednesday, May 14, 2008 - 12:31 pm: |
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David;
I hate to throw a damper on party, but big speed inceases require big power increases. The speed increase you should expect is the square root of the power increase.
To use your case, if you go from 140 to 170 prop hp, you can expect about a 10% increase in top end speed.
Everyone wants more speed, but it comes at a big price.
Rod |
Rod Stewart
Senior Member
Username: rod_stewart
Post Number: 1310
Registered: 08-2006
| | Posted on Wednesday, May 14, 2008 - 12:32 pm: |
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Dvid;
BTW, there is a regular on this site from your part of the world by the name of Peter Chamberlain. Very knowledgeable in the field.
Rod |
David Jones
New member
Username: dunn_dee
Post Number: 2
Registered: 07-2007
| | Posted on Thursday, May 15, 2008 - 05:14 am: |
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We are cruising at around 22mph @ 3800rpm.
Prop size is the largest dia you can fit on an alfa 1 gen 2 - 15 3/4 inch? and 17 pitch mercury mirage.
Yes, the 3.0lt may be the way to go.
Rod, thanks for the info as I now see that the power inc. is not going to make my eyes water as much as the bill for the 2.4lt idea.  !
And I have read a few peices from Peter, he does sound like he knows his stuff.
Thanks all. |
Troy
Advanced Member
Username: troym
Post Number: 512
Registered: 09-2004
| | Posted on Thursday, May 15, 2008 - 06:02 am: |
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Is 3800 rpm what you are seeing at wide-open-throttle (WOT)?
Could be a little too much prop. |
PugetSounder
Advanced Member
Username: pugetsounder
Post Number: 178
Registered: 04-2007
| | Posted on Thursday, May 15, 2008 - 11:13 am: |
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Also you will need to change your OD gear ratio if you're boosting your power by 35-45HP. My current 170-HP motor is mated to a 1.84 OD drive ratio Alpha1/Gen1. I know the 4 cyl 130HP range are usually the 1.98 ratio. That will add substantial $$$ to your swap. |
Rod Stewart
Senior Member
Username: rod_stewart
Post Number: 1318
Registered: 08-2006
| | Posted on Thursday, May 15, 2008 - 12:44 pm: |
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David;
You may want to look at a 220 hp EFI 4.3 V-6 or something along that line if you have room in your doghouse.
The 4.3 will work just fine with the 1.84 drive.
That would give you a healthy 25% increase in WOT speed.
To expand on what Troy said, you should be getting 4800 RPM or so at WOT lightly loaded. What kind of speed and RPM are you seeing at WOT?
Rod |
David Jones
New member
Username: dunn_dee
Post Number: 3
Registered: 07-2007
| | Posted on Thursday, May 15, 2008 - 04:18 pm: |
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We originaly bought the boat 2nd hand with 250hrs and it had a 15 pitch mercury mirage prop - I belive its the same dia. ( we now carry it as a spare).- The previous owner dida bit of tube pulling with his kids, witch explains the 15 pitch. We found we could get to 4800rpm on flat water - (I always start out with a full tank of gas, and there is always 2 people and about 1/4 of the time there is 3 to 4 people, so when we tested the prop we had a full tank and 2 people. With the 17 pitch prop we can get 4400 to 4500 rpm woth the same load conditions, and with 4 generous sized people, a generous esky, 50 or 60 lb of reef fish and just over 1/2 a tank of gas she'll get on the plane happily and sit on 3800 easy.
I didn't think the gear ratio would need to change as the 2.4 revs higher, 6,000rpm wot , and I was dreaming of a cruise of 4300 to 4500 rpm.
I have seen 1 boat the with a 4.3 mpi 220hp (the same as ours) and I belive he services it with tal-ep-a-thy  as there is less than an inch clearance on ea. side of the dog house. ( this boat Haines signature 575F Won the Best boat in its class 3 years running from its release in 95 and they made them the smae until late last year.) So I think the 4.3 V6 is a little bit of over kill or there would be more around with them. but hey 25% inc in speed I'm drooling! |
Rod Stewart
Senior Member
Username: rod_stewart
Post Number: 1322
Registered: 08-2006
| | Posted on Friday, May 16, 2008 - 12:22 am: |
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The 15" prop sounds like the right one for your boat and engine now if you can hit 4800 RPM at WOT. Also your hole shot will be better with the 15" prop rather than the 17"
What top speed are you seeing with the 15"?
Rod |
David Jones
Member
Username: dunn_dee
Post Number: 4
Registered: 07-2007
| | Posted on Friday, May 16, 2008 - 04:46 am: |
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Rod , to be honest I do not remember the top speed with the 15" prop.I do know that we did gain a bit, from memory we got 63km/h ( sorry dont' have the exact conversion to mph) at 4400rpm with the 17.
I'm a little surprised that you would suggest the 15 as the way to go. I thought WOT of 4400 to 4800 was acceptable?
Dont' take it as offence mate, I have alot of respect for you. |
Rod Stewart
Senior Member
Username: rod_stewart
Post Number: 1324
Registered: 08-2006
| | Posted on Friday, May 16, 2008 - 12:37 pm: |
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No offense David;
Whichever gives you the best all around performance is the one you want.
That works out to about 40 mph, which ain't bad at all.
Rod |
