changing from 60hp to 70hp with larger carbs, question for the techs

[phillnjack2]

EVINRUDE 60HP
YEAR 1995
MODEL NO E60TLEOC
OVAL PORT 56 CU IN.
cylinder compression with cold dry engine top 149 - middle 147- bottom149.


At present I get 5900rpm with a 13x19 sst and max speed of just 42.3 mph.
I make that a slip of just around 4%, that I think that is very good with a gear ratio of 2.42-1.
so far so good as the engine is very near the top of its power band and getting around 60hp at the prop.

my engine is a 1995 evinrude 56cu in oval port, and with the smaller venturi carbs that make this the 60hp version.

BUT
I want more power and more top end from this engine, so I am upgrading it to the 70hp version by changing carbs.:rockon:

All three carbs for the 60hp are just 1 1/4 inch venturi, and carbs for the 70hp are 1 1/2 inch venturi.
The larger venturi gives a extra 44% larger volume area than those for the 60hp, and this is where the 70hp is
restricted to being a 60hp engine.
This restriction was the only difference between the 60 and 70hp versions of my 1995 evinrude triple.
ive checked out all the other part numbers for pistons, porting, exhaust, tuner, power pack, timing etc.

i know 100% that the engine can rev to atleast 6400 rpm when i used a smaller pitch prop (13.5x15 alloy)
By using the larger 70hp carbs i would be increasing power by 16% !!! (60 to 70hp)
would this be enough to give me another 500 or so rpm's.

.

 

[Chinewalker]

If you're presently spinning 5900 revs with the 60 carbs, the bump to 70 carbs might well bring you into the mid 6000s. Going up a bump in pitch to a 21P would be the way to go to bring your revs back into the upper 5000 range.

 

[phillnjack2]

that is what I am hoping for, around 6300 to 6400 from the bigger carbs with same prop.
I have a 12 3/4 x 23 that with 60hp can only get 5,000 rpm. if I can get that to around 5800 or more I will be happy.
also got a 13 3/4 x 23 srx but that needs to be on a jack plate realy.
But thanks for that chinewalker, its what I was hoping to hear.
I wouldn't getting another original sst and getting it pitched up unless I can find a 13x21, or maybe a raker .

.

 

[WernerF]

1986 through early 1989 carbs (70hp) have no idle adjustment screw. Try to get later carbs.

 

[flyingscott]

I would check your tach your motor should be rev limited to 6200 rpm also 4% slip on your prop is way low. You either have one of the best set-up boats I have ever heard of or your numbers might be off. 7-8% slip is considered excellent with 10-20% more the norm. One more thing the 70 hp is still rated at 6000 rpm overreving it won't give you more power you will still need to prop it to stay at 6000.

 

[emdsapmgr]

I picked up about 200 rpm's by switching carbs when I added 70 hp carbs to my 60. It's 92 model and the 70 carbs have the idle screws. Great swap. Strong out of the hole. Runs on a 17' Bennington pontoon boat. Tops out at 5850 rpm's.

 

[phillnjack2]

ok first off this is a 1995 oval port engine, nothing like a 92 model.
this has the quick start and S.L.O.W feature on the ignition and from information I have found the limiter is around 6700.
carbs are the latest plastic tops again nothing like the carbs pre 1993.
propeller that gets 42.3 mph is an original 13x19 OMC stainless sst prop with Teflon removed.( it was going rusty) prop has never been modified
speed was measured on a river with two ways using garmin nuvi a garmin gps 12, a tom tom, and a Samsung galaxy s4. all showed within 0.05mph.
rpms verified with 2 different tacho's showing a difference of -+ 25 rpm.
rev limiter is definitely NOT 6200..its a lot higher or certain speeds could never be gained, some people are using these engines above 6800rpm.
Gearing is 100% 2.42 ratio as this is the longshaft engine that was only made with this ratio.
4 % is pretty good, but nothing special for slip figures, just good.
when trying other props like a 13 3/4x 23 OMC silver bullet/srx (srx is just highly polished version) the slip figures were not good at all.
with the srx it was 5500 rpm and 41mph, that gave a slip of 18% so not good at all due to prop being far too low for this type of prop.
second prop tried with bad results was OMC 12 3/4 x 23 pitch, this gave 5000rpm and top speed of 36mph slip was 20% that's terrible.
with both the larger pitch props the engine could not get into its powerband and it just did not do what was expected of it.

For the engine to be limited at 6200rpm with the 15 pitch prop it would need to have a slip figure of just 3%, with this being a normal omc alloy
prop I doubt that is possible, but rev counter was not used for this speed test !!!!

here below is a link to video of the boat with the 13.5x15 pitch alloy prop from zero to plane and out of sight.
I get same holeshot with 13x19 pitch too, but this video gives an idea of how the engine performs with 15 pitch.
top speed in this video is just 36.5 mph.
(By the way don't expect to see a race boat hull, this is a cathedral hulled Orkney dory 13ft 3 in).

https://www.youtube.com/watch?v=nh9GCaU41l8

.

 

[phillnjack2]

No Title

here is a few pics of props used for my speed tests.
all props are 13 spline

 

[David Young]

Nice video, i gave it a thumbs up