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  merc efi 60 4-s vs yam 70 performance on a 15

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Author Topic:   merc efi 60 4-s vs yam 70 performance on a 15
chrisb posted 09-08-2002 07:37 PM ET (US)   Profile for chrisb   Send Email to chrisb  
I'm confused about how these two engines would differ. If I'm correct the 60 has a bigger displacement (6o) vs the 70 (51). I read all related threads from the last two years last night till 3 am. I gathered there is no replacement for displacement, the fours have better torque, the efi gives even more efficiency, mercs are generally faster,and the fours are possibly a little stingier on gas, so you would think it might be the better motor for someone who frequently takes adult slalom skiers for a pull. Yet that seems counter intuitive. Has anyone tried to pull a slalom skier on a 60 merc efi four on a 15 sport? if not would any of you sages venture a guess on the pors and cons of each?
David Jenkins posted 09-09-2002 11:39 PM ET (US)     Profile for David Jenkins  Send Email to David Jenkins     
What's most important to you? If you want to go 47 mph, have an incredible hole shot and the best engine for skiing, you'd get the Yamaha 70. If, on the other hand, 38-40 mph is adequate and you want an engine that is so smooth and quiet at idle speed that you have to look at the telltale to see if it's running, go for the Merc 60 EFI 4-stroke.
chrisb posted 09-11-2002 08:22 AM ET (US)     Profile for chrisb  Send Email to chrisb     
I dont care about speed so much as torque and ability to pull the skier. My wife drives and I'm pretty strong when I cut, she has to overcorrect like crazy to keep the boat straight with the old 48 johnson. Does the speed of the 70 resist that better or the torque of the four stroke or is it just weight of the boat? Does any one know how fast their 15 goes when pulling a slolam skier? Ive never has gps or speedometer.
David Jenkins posted 09-11-2002 09:18 AM ET (US)     Profile for David Jenkins  Send Email to David Jenkins     
Either new engine will be a vast improvement over the old Johnson 48. You should be able to go fast enough to barefoot with either setup. To keep the boat from turning (and bogging down) while you are cutting, the added weight, bigger displacement and better torque of the 4-stroke would be ideal for this application. Consider using a setback bracket for even better performance.
DaveH posted 09-11-2002 10:44 AM ET (US)     Profile for DaveH  Send Email to DaveH     
Chrisb:

The straightline characteristics of the boat while slalom skiing will be affected more by the skier than the engine. The 15 and 13 especially so due to the very shallow draft. and low weight. Therefore, regardless of which engine has more torque, your wife will still need to overcorrect her steering with either engine.

The hole shot will be quite different and unfortunately, I have no advise to offer since I do not have experience with a 4s while skiing. In reports I have read, the hole shot with a 2s is normally quicker to plane but adding a skier behind may reverse that with the torque differences.

Bigshot posted 09-11-2002 11:49 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I had a 70 2s on mine and my buddy could damn near pull it sideways. It has NOTHING to do with the engine....that is all boat design and weight. A stronger heavier engine may help due to higher speeds, etc. But it may also make it more dangerous. If you are now going 5mph faster and your wife can't steer.....you get the picture.
chrisb posted 09-11-2002 04:25 PM ET (US)     Profile for chrisb  Send Email to chrisb     
Fortunately my wife has no hesitations about
cutting the throttle and sinking me if there is any traffic within a 1000 ft. She doesnt
go too near shore either, but beggers cant be choosers. She however is not as strong as I am and struggles getting up on fatboy skis.(160 LBS) Is there enough hole shot with the merc 60 EFI to make it easier for her to climb out of the water? What would the ski speed be with WOT for the merc or yam? If I could do 32-34 with the merc then I would buy it. Thanks for all the help so far.
DaveH posted 09-12-2002 09:53 AM ET (US)     Profile for DaveH  Send Email to DaveH     
chrisb:

I think you have an answer to your question from your statement:
She however is not as strong as I am and struggles getting up on fatboy skis

I know for a fact that a 70Hp 2s will pull me out of the water very quickly and I outweigh your wife by 30 lbs. I cannot vouch for the 4s and the hole shot as I mentioned before. I estimate both engines will pull a skier at least 32 mph but getting on plane (with skier intact) for your wife is an issue with the present 48Hp. I would recommend the 70Hp 2s without any fear of subpar performance that you are experiencing now.

chrisb posted 09-14-2002 10:08 PM ET (US)     Profile for chrisb  Send Email to chrisb     
Since the new fours are heavy in the 70 hp category my wife suggested I get a used 70 yam and see what changes in the next few years. Assuming I can find one around here, is there anything in particular to watch out for? Whats a compression test and what values are worrisome?
chrisb posted 09-14-2002 10:09 PM ET (US)     Profile for chrisb  Send Email to chrisb     
Since the new fours are heavy in the 70 hp category my wife suggested I get a used 70 yam and see what changes in the next few years. Assuming I can find one around here, is there anything in particular to watch out for? Whats a compression test and what values are worrisome?

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