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Author Topic:   4 stroke weight variations
jimithing posted 02-24-2004 02:35 PM ET (US)   Profile for jimithing   Send Email to jimithing  
Why does the weight of 4 strokes vary so much between brands?

Suzuki, Yam's Merc's(although lighter than others) in the 70-90 hp range all vary greatly in weight. Why is this since many of the blocks are identical?

Wouldn't be so concerned if I didn't want the stern of my whaler getting sucked under when I back down.

lhg posted 02-24-2004 02:59 PM ET (US)     Profile for lhg    
It's mostly based on the size of the block the given HP is derived from.

Take the 60 HP engines:

The 360# Suzuki 60 is based on a block that also gives 70-HP

The 260# Mercury is based on a block that also gives 50HP.

Take the 70 & 75 Hp engines:

The 360# Suzuki 70 is based on a block which also gives 60HP

The 370# Yamaha 75 is based on a block which also gives 115HP

The 90 HP Yamha is also based on a block that gives the 115HP

But the heavier 90 HP Suzuki is based on a block which gives the 140HP, so it's larger.

The 386# Merc-aha 115 EFI has the best HP to weight ratio of any of them in the mid-ranges. It only weighs 27# more than the Suzuki 70, a negligible difference in most situations.

Moe posted 02-24-2004 05:52 PM ET (US)     Profile for Moe  Send Email to Moe     

Honda 40/50 808cc 198 lbs
Suzuki 40/50 815cc 238 lbs*
Merc 50/60 995cc 248 lbs*
Suzuki 60/70 1298cc 335 lbs*
Honda 75/90 1590cc 373 lbs
Yamaha 75/90 1596cc 370 lbs
Merc 75/90 1596cc 386 lbs
Merc 115 1741cc 386 lbs*
Yamaha 115 1741cc 402 lbs*
Suzuki 90/115 1950cc 416 lbs*


lhg posted 02-24-2004 07:03 PM ET (US)     Profile for lhg    
Moe - Suzuki must have been low-balling the 60/70 weight previously, as the 2004 catalog shows them at 359#, dry.
Moe posted 02-24-2004 07:20 PM ET (US)     Profile for Moe  Send Email to Moe     
Thanks, Larry. Looks like they need to update their website.
jimh posted 02-24-2004 08:58 PM ET (US)     Profile for jimh  Send Email to jimh     
Moe--thanks for the data.
jimh posted 02-24-2004 09:09 PM ET (US)     Profile for jimh  Send Email to jimh     
Also see:

Moe posted 02-24-2004 09:21 PM ET (US)     Profile for Moe  Send Email to Moe     
Thanks for aligning it, Jim.
Perry posted 02-24-2004 09:34 PM ET (US)     Profile for Perry  Send Email to Perry     
Good data Moe. It is interesting that the Mercury 75/90 HP at 1596 cc weighs exacty the same as their 115 HP and 1741 cc engine. Misprint or coincidence?
Moe posted 02-24-2004 10:36 PM ET (US)     Profile for Moe  Send Email to Moe     
I believe the reason the 75 and 90 weigh the same as the 115 is that they're they same engine as the 115, just destroked. That means they have longer rods and/or taller pistons than the 115, which may have offset the slight additional weight of the 115's EFI system over the 75/90 carbs.


Perry posted 02-25-2004 12:15 AM ET (US)     Profile for Perry  Send Email to Perry     
That's what I mean. Don't longer rods, taller cylinders and fuel injection on the 115 weigh more than the carbed 75/90?
Bigshot posted 02-25-2004 11:27 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
The Suzuki 140 is the same as the 90 but weighs like 10lbs less due to the amount of metal they removed boring it bigger.
Moe posted 02-25-2004 12:26 PM ET (US)     Profile for Moe  Send Email to Moe     
Perry, it's the destroked 75 and 90 that have the longer rods and/or taller pistons, not the 115.

When an engine is destroked, the crank pins that the rod journals attach to are moved closer to the centerline of the crank. This means that at top dead center, the piston would be below the block deck and the head's combustion chamber, by half the decrease in stroke, unless the rods are lengthened and/or taller pistons are used to bring the top of the piston back to the block deck at TDC. If the same heads and combustion chambers are used, these pistons even have to be domed to restore the compression ratio lost to the lower swept volume.


jimithing posted 02-25-2004 01:04 PM ET (US)     Profile for jimithing  Send Email to jimithing     

Lost me there guy.

So am I to assume that the former older Yamaha 100 4s weighs less than the current Yamaha 90 4s, which replaced it? Or not....I see the 115 is heavier by at least 32lbs.

This is confusing enough for me to be compared to time travel....

lhg posted 02-25-2004 01:34 PM ET (US)     Profile for lhg    
When the first Yamaha mid-range 4-strokes came out, they were not only lowballing the weight, but overrating the HP on the 80/100's, which is good for both sales and pricing (pay a lot more for a supposedly lighter weight engine). But now they evidently have both the weight and HP right, (75 and 90, as Mercury has used from day one on same powerhead) probably from market pressure and complaints.

The 115 Yamaha is heavier than the Merc model because they put the V-6 shaft and gear case on it so that they can offer Counter rotation. Mercury has never done this with any of their 115's, always staying with the 4 1/4" non-CR gearcases. This can be both good or bad, depending on what you want to accomplish. For single power, it makes no sense and hence lighter weight Merc 115 is a much better deal both price and weight wise. If you're doing twins on a larger, heavier boat, the CR is valuable and the weight is not a problem.

I have just noticed in the 2004 Mercury catalog that the new 75 & 90 HP Optimaxs are 360#, which is the same weight as the popular Suzuki/Johnson 70 and 55# heavier than the Evinrude E-tecs, but lighter than any same HP 4-strokes. As noted on the Suzuki's, this 360# is not a big problem on a Classic 16/17 or larger boats, so these new 3-star Mercs could be another option to be looked at for Whaler re-powers as conventional 2-strokes disappear. Since the Optimax and Etec 75/90's are fuel injected, these could be popular over the carbed & heavier Merc-aha 75/90 4-strokes.

Perry posted 02-25-2004 02:25 PM ET (US)     Profile for Perry  Send Email to Perry     
Moe, I agree with jimithing. A little confusing. I was told that the 115 was a stroked version of the 75/90. Same bore but longer rods and taller cylinders on the 115 which increased it's displacement by 145 cc. I assumed that this would have increased it's weight.
lhg posted 02-25-2004 03:05 PM ET (US)     Profile for lhg    
The overtone here is that Mercury couldn't be any more honest than the Japanese, and are falsifying the weight on their 4-stroke motors like the Japanese have evidently been doing for years. This could be true, I suppose. You decide, or even better, weigh your motor with oil in the crankcase.
Moe posted 02-25-2004 05:41 PM ET (US)     Profile for Moe  Send Email to Moe     
Perry, whether the 75/90 is a destroked 115, or the 115 is a stroked 75/90, is just a matter of perspective if they were designed simultaneously. Looking at the differences in the engines, from a production standpoint, it would make sense to use the same block (same cylinder length) AND rods for both 75/90 and 115, with different cranks and piston heights. Differences in compression could be handled either by using different heads with smaller chambers for the 75/90 and larger chambers for the 115, OR by doming the smaller displacement pistons or dishing the larger displacement pistons.

As I said at first, this is how I _believe_ they do it, not that it IS how they do it. For example, I can take my 95" Harley to 106" with the same cylinders.

lhg posted 02-25-2004 06:02 PM ET (US)     Profile for lhg    
Here's another puzzle for you guys to figure out.

Mercury's new 75, 90 & 115 Optimaxs have IDENTICAL specs in the 2004 catalog, literally identical. Yet the 115 weighs 375 while the 75 & 90's weigh 360. How do they do this?

Moe posted 02-25-2004 07:38 PM ET (US)     Profile for Moe  Send Email to Moe     
Larry, they're all three listed as 375 lbs in the specs on the website.
lhg posted 02-25-2004 08:08 PM ET (US)     Profile for lhg    
So now both the Mercury and Suzuki printed catalogs differ from the web. Guess we can't trust any of these engine guys to treat the consumer fairly. I'm going to complain to the FTC about deceptive advertizing & marketing.

Do we really think there is a 64# difference between the 250 HP Suzuki and the 250HP Verado? Makes me wonder who is on the level and who is not. Does that E-tec 90 really only weigh 305#? Maybe Mercury is knocking down the weight of the Opti 90 to look better against the E-tec 90?

We'd probably all be shocked if we actually weighed our outboard engines, with oil (gearcase, crankcase and/or under cowl oil injection) and props as actually installed on our boats!

Perry posted 02-27-2004 04:17 PM ET (US)     Profile for Perry  Send Email to Perry     
"from a production standpoint, it would make sense to use the same block (same cylinder length) AND rods for both 75/90 and 115, with different cranks and piston heights."

That's new to me. My F150 has a 5.4 V8. My dad has the same truck with the 4.6 V8. Same bore but the 5.4 has a TALLER block. My motorcycle (Yamaha RD400) has the same bore and uses the same pistons as the RD350 but has a TALLER block.

I wasn't aware that in some applications displacement can be increased or decreased by adding longer or shorter pistons and rods while using the same block.

alkar posted 03-08-2004 01:11 AM ET (US)     Profile for alkar  Send Email to alkar     
Sheeesh. I hope Honda is being honest when they advertise the weight of their 115 at 505 pounds. I'd hate to think it could be even worse...

Of course, that might explain why it looks like somebody parked a Mack truck on the transom of my boat :-)

LHG posted 03-08-2004 02:31 PM ET (US)     Profile for LHG    
Yea, but Alex you've got to look at it this way. You're helping the environment and conforming with CARB & the EPA.
I'm glad you're doing it so I don't have to!

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