v4 x-flow cav plate(s)?

[pcrussell50]

Re: v4 x-flow cav plate(s)?

ok, I was too verbose. if my tach is set on 4, when it should be set on 6, will it read uniformly 1/3 higher than reality at all rpms? or will it just give screwy nonsense readings all over the place that cannot be mathematically corelated to reality?

-Peter

 

[ezeke]

Re: v4 x-flow cav plate(s)?

ok, I was too verbose. if my tach is set on 4, when it should be set on 6, will it read uniformly 1/3 higher than reality at all rpms? or will it just give screwy nonsense readings all over the place that cannot be mathematically corelated to reality?

-Peter

The readings that you are giving are unrealistic.

I have set my engines too high in attempting to compensate for too much pitch with the result of having the prop not bite and running the engine too fast. This sometimes happens in rough water or when crossing someones wake.

All of the Standard pre-1996 OMC and teleflex tachs that were capable of being set to 6p should have been set to 6p for your engine or any V4 with a similar ignition system. See page 6 here: http://www.downloadingfiles.co.uk/t...structionmanuals/99320 rev 10 Tachometer,.pdf

 

[pcrussell50]

Re: v4 x-flow cav plate(s)?

The readings that you are giving are unrealistic.

I have set my engines too high in attempting to compensate for too much pitch with the result of having the prop not bite and running the engine too fast. This sometimes happens in rough water or when crossing someones wake.

man, this is cornfusing...

when i started this thread:

-i had not yet raised the motor
-the anti-cav plate ran completely submerged... so deep it was completely invisible
-there was a hellacious forward and sideways spray until i trimmed her a good bit nose up, once planing
-my 21" stainless prop [of unknown brand], would go right past redline in steady cruise so that i had to run a good deal below full throttle
-my 22" omc raker prop would go right past redline in steady cruise so that i still had to run throttled back
-my 24" omc raker prop would finally allow full throttle operation as long as i had the weight of two more folks in the boat with me. it would run at a steady 6100 rpm

on a hunch and a suggestion, i raised the motor so that the anti-cav plate was about a half inch above the bottom of the transom, [as well as 6" set back]. the results:
-the anti-cav plate became visible in cruise, just skimming the surface of the water
-the horrible forward spray before going nose-up trim was gone
-with the 24" prop, i could run full throttle with 3 aboard, and it would not go past 6100rpm, [no change from before raising the motor].
-the boat picked up a couple of mph
-no blowouts in light chop with no waves

based on this, i'm guessing i haven't raised it too far. what do you think?

-peter

 

[Dhadley]

Re: v4 x-flow cav plate(s)?

You are kind of avoiding telling us what tach you have so that's leading us to start to think you may have the wrong tach completely. At any rate the readings you are giving don't compute. Everything is based off of your baseline, which is speed and rpm. That can be calculated to percentage of slip. Those numbers are off considerably based on experience. Once you establish a good baseline then you can lay out a plan to make the rig as efficient as possible.

Based on the motors I've seen running with the (correct) tach set on 4 the readings were close at or near idle but way off on top. We never calculated how far off - it doesn't matter. It's wrong and needs to be corrected so you can make intelligent decisions on changes from that point on.

 

[Chris1956]

Re: v4 x-flow cav plate(s)?

OK, it sounds like you have a reasonable motor height. Let's get that tach reading correctly and see what your real RPM is. We can then suggest additional tweaks.

 

[pcrussell50]

Re: v4 x-flow cav plate(s)?

ok, guys. you've been very patient with me, and i appreciate it immensely. part of why i posted to begin with is the sense i had that my readings were nonsensical, and i wanted to bounce them off of you guys to see what i could rule out and what i couldn't. i think that has been a success. the tach is the number one suspect now thanks to you all.

fwiw, i'm not trying to avoid talking about my tach. it's just that early yesterday[tuesday], i left the lake where i keep the boat, so i can't tell a thing about the tach until i get back there, [wife's grandparents house].

interesting development for what it's worth. on a hunch, i performed a calculation:
IF the tach is set to 4 instead of 6... AND if it's true that when i THINK i'm doing 6k, i'm really only doing 4k, then the speeds i calculate, [using a 10% slip and 4k rpm], correlate very closely with what i'm reading off the gps.

say, if it comes to it, and the tach is not set wrong, but is plain old "done gone bad", what tach should i look at for a replacement? factory replacement or are there better alternatives here in the current decade? i use autometer gauges on my race car, for example.

-peter

 

[Dhadley]

Re: v4 x-flow cav plate(s)?

Auto gauges should stay in cars. A good 2 stroke tach is what you're looking for. The tachs from OMC, now BRP, are considered to be among, if not the most accurate in the industry. That being said, there are cheaper tachs that have a larger margin of error. Some are as much as 5% plus or minus.

 

[pcrussell50]

Re: v4 x-flow cav plate(s)?

Auto gauges should stay in cars. A good 2 stroke tach is what you're looking for. The tachs from OMC, now BRP, are considered to be among, if not the most accurate in the industry. That being said, there are cheaper tachs that have a larger margin of error. Some are as much as 5% plus or minus.

roger on the automotive tach thing. i just used it as en example of where i trust an aftermarket gauge more than on oem gauge. i am too new to boating to know if the same applies here. that's why i rely on you guys. how are teleflex tach's? or are they considered "cheaper"?

-peter

 

[Dhadley]

Re: v4 x-flow cav plate(s)?

Personaly I use OE tachs, especially on multi engine deals. The T-Flex tach is better than some but we're back to the "get what ya pay for" as far as accuracy. On the other hand we may be getting way ahead of ourselves - lets see what the existing tach is set on first.

 

[pcrussell50]

Re: v4 x-flow cav plate(s)?

Auto gauges should stay in cars. A good 2 stroke tach is what you're looking for. The tachs from OMC, now BRP, are considered to be among, if not the most accurate in the industry. That being said, there are cheaper tachs that have a larger margin of error. Some are as much as 5% plus or minus.

Unless my mental math is wrong, that means a cheap tach that has a 5% error would be reading 25 rpm off at about 5000 rpm. That's actually not as bad as i would have thought.

-peter

 

[pcrussell50]

Re: v4 x-flow cav plate(s)?

What is the tach set on? Assuming it's the correct tach it should be set on 6. If it's set on something else like 4 - or not the right style tach - then you'll get some wierd readings.

ding, ding, ding! i just got back from the lake. not only is my tach NOT set on 6, it doesn't even HAVE position number 6!? it only goes from 1 thru 4. AND it was on position 1. someone put the wrong tach in this stripped down, old performance hull.

i took the boat out, this time with a 22" pitch omc raker and a handheld gps. using an online prop calculator and an assumed 10% slip, i presumed i could get into the mid-50's without much danger of too many rpm's, [since my tach was going to be unreliable anyway]. i got it up to about 52 before it started to "wobble" or "walk". i assumed it was the onset of chine walk and backed off. so i did it several more times and the same thing happened each time. i am going to have to learn how to drive this thing and re-rig some controls so i can have both hands on the wheel.

52mph feels REALLY fast with no windshield in a little low profile v-hull boat, putting your butt close to the water level.

-peter

 

[emdsapmgr]

Re: v4 x-flow cav plate(s)?

Possible you are getting into the chine walk area now. That means the hull us running easily over the water. Now you can spend your time learning how to drive through the chine walk problem. You may find that the faster you go, the more the oncoming air will hold the nose up, stabilizing the boat. It will be interesting to see what your actual tach readings are. At one time I checked two of my teleflex tachs with a special industrial optical scanner and found them both to be off unacceptably. They were off throughout the entire range. One read fine at mid rpm's the other better on top-but were off over 250 rpm elsewhere. I finally broke down and bought an OMC digital Quartach tach: 175756.

 

[pcrussell50]

Re: v4 x-flow cav plate(s)?

I finally broke down and bought an OMC digital Quartach tach: 175756.

i can't seem to google anything related to that part number. further, i can't seem to get much at all with OMC tachs. tons of faria and teleflex tachs and rarely an omc... or at least i think they are omc. where's the best place to shop for real omc tachs?

-peter

 

[ezeke]

Re: v4 x-flow cav plate(s)?

i can't seem to google anything related to that part number. further, i can't seem to get much at all with OMC tachs. tons of faria and teleflex tachs and rarely an omc... or at least i think they are omc. where's the best place to shop for real omc tachs?

-peter

Try: http://www.marineengine.com/newparts/part_search.php

 

[pcrussell50]

Re: v4 x-flow cav plate(s)?

zeke, thanks. they have that very tach that was recommended. and it isn't _that_ much more expensive than a cheapo faria, really.

-peter