'75 high compression V4 crossflow intake stuffers and pump gas?

[pcrussell50]

So I have this '75 bubble back 135, totally stock. Used to be our daily driver family boat motor (on our 16' Sidewinder LowPro clone). Haven't really used it since a couple of years ago when we started using our 18' Bahner bowrider with a 2.0L 150.

Anyway, so two years ago just after I last used my V4 135, I took off the intake and put some Chris Carson reeds into it. While I was at it, I put in some of those intake stuffers that I had lying around, the kind that came in the '77 140hp.

My question is, since I pretty much only run 91 pump in that motor, do the stuffers increase my risk of detonation? It is generally run on Lake Mead which is about 1100 feet above sea level. I have a '93 bubble back (115 hp) that I can put them in, instead, if that is a better match... And it sounds like it probably is.

-Peter

[flabum1017]

The stuffers won't be the problem, it will be the higher compression (if it doesn't have the thicker head gaskets) and the high ring pistons in the 135............ 91 should be ok, bump the timing back a couple degrees to be sure

[pcrussell50]

Great tip as always, 'Bum. Where do I get the thicker head gaskets? Part number? ProMarine maybe?

EDIT: These? http://parts.promarineusa.com/CGI-BI...AF202D+M50+ENG

-Peter

[FMP]

High ring, hc heads, gaskets what's the cranking psi?

[Mark Poole ModVP]

The '75 135 should not have high ringers but the '77 140 did. If you have ever noticed, there are hardly any 140's still running (original). I still see old 85 and 115's running. Between the bigger ports, the high ringers, and the extra H.P. most are long dead! They told us at OMC school to turn the timing back 2 degrees. I miss the cross flow motors from the '70's. Excellent power to size ratio and simple to troubleshoot and fix.

[FMP]

Not too many originals but it had been 40years. So hc motors are 155-165 psi? If you don't feed them good fuel ...... 165-175 is max for 93-94 gas in my Chryslers with lots of ign. Don't load them , let them spin. That's at 583' .

[pcrussell50]

Glad it's not a high ring piston. But I suppose I should check compression before I go to thicker head gaskets or anything else, just to get a ballpark of where I am in cranking pressure. Thanks, so far, guys.

I have a couple hundred hours on this motor, and who knows how much before I bought it? Most of it at family recreational boat rpm's. But I've done a few full power/speed runs. It GPS'd in the Sidewinder LowPro, with just me, at just under 55mph. And was juuust getting "walky", but still super easy to control at that speed. Glad it stayed together.

-Peter

[flabum1017]

They went to thicker head gaskets when the government took the lead out of the gas..............

[DanUmbarger]

I've had the same questions about my 1975 135 Johnson on my 16' Hustler Victor. Mine is also stock and I'm running 91 octane at 40:1 TCW3 oil. So what is the consensus? Go with the thicker head gaskets...drop timing 2 degrees...run 91-93 oct...all of the above or a combo of some of them???

[Mark Poole ModVP]

As FMP said, don't load them. I have seen people run a bigger prop because it gives them 2 mph. Better off without that extra 2 mph and let the motor turn up where it should. The bass boat crowd is bad about this. They want the biggest prop they can turn for the top end speed, then when they are not fishing they pull the kids on a tube.
The older cross flows have big jets so they are getting plenty of fuel. Turn timing down 1 to 2 deg. and run a can of engine tuner through it once or twice a year. Nice thing about the cross flows, you can easily take intake transfer covers off and do a good inspection of the pistons, rings and cylinders.

[FMP]

What's psi spec for those hi comp v4?

[Mark Poole ModVP]

The older engines and the high ring engines would have 150 to 160. My dad had a '79 85h.p. That was a strong 85 but it had high ringers in it and we pulled them out before they failed.

[FMP]

I run the Chryslers with Wisecos. Not high ring but still 165+ with just a touch from the head. Factory spec is 155-165, some had high ring some not. Also have a three ring 105 that's 145psi, will never drop a psi with that one, also doesn't have the front case stuffers but you wouldn't know it the way it runs.

[DanUmbarger]

Just did a compression test on my 135 ( was winterized and fogged 3 weeks ago) and it had 125# on 1,2 and 4 and 130# on 3....this is with the gauge I normally use now.....I have 4 gauges and they all read differently. Once I do a compression test on a motor that had water in it it seems to kill the gauge. This gauge hasn't been subjected to water "yet"! This test was done cold and throttle plates closed...tried opening wot and only seemed to raise them 5#s or so...how are you guys testing compression? Normally when I do a comp test its cold and am just checking cyls for any low cyls then delve into them if needed. I strongly agree with the use of engine tuner...have brought both ob's and sterndrives back to life with it.

[FMP]

I do it cold , throats wide open, best would be no fuel but don't like to spin it dry, strong battery. Gauge should top out 3-4 revs. Fogger will increase your numbers.
130 fogged doesn't seem too high , I'd get it up another 25 psi but doesn't mean you should.