302 HO WOT RPMs

scuba4me

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Ok its been a year on the rebuilt motor in my boat lots of use no issues its an inboard with a 302 HO 1409 carb 20' Sham PH (asked on that site but looking for a bigger crowds opinion). Boat has never seen past 3500RPM while on the water in gear. It will snap past 4K out of gear just fine. I'm looking for thoughts on this. I have had various opinions ranging from "it seems fine just enjoy it" to "something's not right you should be over 4K on water in gear at WOT" Heres the deal:

Its almost like there is a limiter on the motor when it hits around 3300-3400 in gear on the water, and I can just hear the secondary's open around 3200. Have tried 3 different pitched props 13x11-13x13 stock is 13x13 all hit same RPM's within a 100 or so 3500 with 13x11 but did not feel right power wise (just top speed changes) 13x13 on there now load in the boat (400lb or 1000lb) does not mater still just hits 3300. All cylinder are firing and motor runs great lot of power. I just think there is more to be had but maybe not - speeds 30-32mph or so at 3300. I'm using timing light and digital tack to make sure of a correct reading. I'm cruising at 2600-2800 at 24-25mph gas consumption is fine.

Things I have tried/done:
New Malory electric distributor, plugs, wires, coil and alternator
Checked vacuum to timing adjustments - vacuum at idle is around 15.
New fuel system - filter, pump pressure is regulated at 6psi per Edelbrock (also tried pressure wide open at 11psi no difference)
Total timing is 30
The BW 1:1 trans is 1 year new
Bottom is clean but it is painted

What do you all think should I stop thinking about it and just go fish or is there something I'm missing?
 

southkogs

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Shamrock is a direct drive on a semi planing hull, right? She's probably built and propped for torque more than for speed. I'm thinking you're in the right ballpark. You might get more RPMs playing with diameter, and then pick up a little speed adding some pitch ... but I'm not sure that hull is really set for that sort of thing. Low 30's sounds kinda' good for a pilot house.
 

scuba4me

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Thanks for your input. I really appreciate it and your giving me confidence. The PCM manual says 4400 WOT I know back when it was new that might have been the case but its not new its an 80's haha, so I think your right. I've just heard so many say the opposite I needed to hear form guys like you.. Yes semi planning hull direct drive. After 30 its a little sketchy anyway, so I'm usually running at 25-26mph in the ocean. I kind of just wanted reinforcement that WOT at 33-3400 is ok and I don't have another 900 left somewhere. The marine reman was made to have low-mid torque - I asked for that and its obviously what I got.

I am wondering if running it at WOT would be a bad thing like if I took it to a lake. Is my WOT 3400 RPM equivalent to the max RPM of 4000-4400 in terms of being bad for long term running durations?? OR am I ok spinning it up that high for a long run?
 

Scott Danforth

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you should be closer to the 4500 RPM. my first thought is that the tach is off. however you confirmed it with your digital timing light.

when the motor was rebuilt, did the cam get timed properly?
 

sub2010ss

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Worst part about the forum community is getting widely ranging advice. But Id have to agree with Scott, you should be able to pull higher RPM, especially out of a 302. Is she firing on all cylinders?
 

Bondo

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The BW 1:1 trans is 1 year new

Ayuh,.... I'd have expected a 1.5:1, rather than 1:1 gear ratio,....

That alone would put the motor's rpms 'bout where they oughta be,...
 

scuba4me

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Bondo 1:1 is stock trans ratio for the boat I don't believe that's the issue.

Scott Danforth: I sure hope so. You mean is it off a tooth or something right? I did notice the dots lined up on the gears but I didn't do the work its a reman I ordered.

sub2010ss: That's a good call I put new plugs in tonight. #7 looked a little too unused to me (one of these things is not like the others deal). Might have been a bad plug. Wont know until tomorrow. I took the MSD out. If one cylinder was not firing well under load that would account for the 600-800 missing WOT rpms right? All plugs looked right just #7 no brown on the electrode. Will do plug wire check if it still seems like the spark is not enough ext. No vacuum leaks I can find PVCs off the carb. #7 looks like its been working a little could have a cracked porcelain or something.. Hopefully its not valves over tight or something. I will compression check leak down first if this does not solve it. Thanks for the tips Ill post back my findings.
 
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Bondo

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#7 looks like its been working a little could have a cracked porcelain or something..

Ayuh,.... A very clean spark plug can be a sign of water ingestion,.... worth lookin' into,....
 

scuba4me

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Well I put new plugs in and for sure #7 is firing different and the vacuum increased from 15 to 17 after retuning its running the best it has since I put the motor in last year. No water intrusion going on. All plugs looked perfect and the same except #7 did not have the little brown spot on the electrode no hints of water, rust ext just #7 looked like it was not firing at higher RPM - no total timing mark on the electrode like the others. It just had the base mark up by the tip. Its the hardest plug to put in and remove so I might have cracked it when putting it in before. Was very careful this time hopefully that's it. The only thing left that's not new is the flame arrestor. Its clean but its always seemed like it might not be enough air flow. Its on the list I will take it off and run it to see if the RPMs go up. As of today the only thing that's over a year old on the motor is the main pulley and the spark arrester...

Two other things I noticed is after it was warm: Fuel pressure went from 6 down to 5 so I readjusted while warm back to 6psi. Also, the choke was not quite all the way open 1/8-1/4" off vertical once at running temp. On my carb 1409 the secondary's wont fully open if the choke is on. I'm hoping that could be part of it as well - fixed it by adjusting the choke. Had to go counter clockwise 2 notches to the left of the index to get it to go fully open. I did not see any other adjustment for the choke.. The accelerator pump linkage is on the hole closest to the carb there are 2 other holes further out and lower. I'm not sure if moving that to the center would help but its on the list now.. Ill get back with on the water WOT RPM results as soon as I can get out there. Windy and stormy right now..
 

old bird

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Check your throttle linkage. With engine off. Take the flame arrestor off, have someone advance the throttle and verify it is opening fully.
 

scuba4me

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Thank you but making sure I have a full pull on the throttle with the choke secondary stop out of the way was one of the first things I did. If the choke is not fully opening I might not be getting the secondary's open - crossing my fingers on that being it.. There is only about a 1/4" of throttle movement on the secondary's so it would be hard to tell when running. I hear a little boost up at WOT but with the carb I have it should not be a noticeable secondary boost like with a Holly. I might need to run it in gear up against the trailer to look in there as it would be very hard to have the seats up and look while going fast enough on the water.
 

old bird

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Its almost like there is a limiter on the motor when it hits around 3300-3400 in gear on the water, and I can just hear the secondary's open around 3200.

carb not fully opening ???
 

scuba4me

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Yes that's an obvious possibility that I have ruled out with the exception of the secondary butterfly's not opening all the way due to the choke. I'm 100% sure the cable is opening the carb all the way, but I have no ez way of checking secondary operation under load on the water. Possible I fixed it today with the choke adjustment..
 

sub2010ss

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Interested in hearing how it turned out. I have the same carb and had the same problem with my choke. I don't fully understand how these chokes work but adjusted mine so it is full open when its up to normal operating temperature. Didn't seem to make a difference on the pull on the top end. I know I can certainly hear the secondarys opening on mine.
 

scuba4me

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That's encouraging to hear. I'm betting on it being a cracked ceramic in #7 plug. Looks like Ill be finding out where I'm at on Saturday. Ill post up the WOT RPM. Had someone tell me the other day that a prop shop could tune my prop to get me up to the 42-4400 RPM, but I'm still not buying the prop pitch is the issue, and I'm not going to a 13x9 from a stock setup of 13x13 ha..
 
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scuba4me

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So the good news is the motor is running way better my buddy commented on the less exhaust smell and the power through the throttle range has increased probably all due to new plugs smaller gap and the new Mallory. I gained some mpg and speed. RPM's are up a couple hundred so I'm still stumped there. Running really well temp, oil pressure ext. all perfect on a 70 mile round trip with 5hrs of trolling at 2-3mph. Others with the same hull are saying they are going 30mph at 4000rpm I'm getting there at 3200 (tested with 4 tachs now). The boats stock prop is what's on there now 13x13. To gain 800RPM Id need a 13x9 or so I think and I don't even know if it would help I might end up with 24mph at 3300 and that's it.

The only thing I can think of to try next is just to get on some glassy water with the sets up and arrester off and go WOT to look at the secondary air flap and maybe push it down if its not fully open and see what happens. The secondary's butterfly's are opening, but I here some guys are drilling out the counter weights to get the air flap to fully open. Going to test before drilling.

For what its worth the place I got the reman from told me this: "If your motor is running well, has enough power, your happy with the performance, speed ext. the mid 3K RPM's WOT is ok. Your motors cam and heads are setup for mid range power its fine" Not sure if they are just telling me what I want to hear, or if they are being honest.
 

scuba4me

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Talked to ACME and another source turns out I'm over propped by 3 pitch's. RPM curve is way off. The cup on my current 13x13 makes it more of a 13x14.5 and my 13x12 is more like a 13x14! I ordered a ACME 913 13x10.5 that should solve my issues..
 

Bondo

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"If your motor is running well, has enough power, your happy with the performance, speed ext. the mid 3K RPM's WOT is ok. Your motors cam and heads are setup for mid range power its fine"

Ayuh,.... That's completely Untrue,..... The motor Has to be Able to spin to full Wot Rpms, or it's Luggin' thru-out the entire rpm band,....
 

scuba4me

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My 913 arrived I just ran it yesterday for the first time finally my RPM curve is right on this boat! I was getting max apprx 3300 and 31mph at WOT the OJ 13x13. I gained 4-5mph top end with the 913 and at my 4K rpm target I have been looking for over the past year.

Old 13x13 OJ Prop and the ACME 13x12 .80 cup I tried:
5mph at 700
10mph at 1300
15mph at 1800
20mph 2300
25mph at 2700
31mph at 3300

New 913:
4mph at 700
10mph at 1800
15mph at 2200
20mph 2800
25mph at 3100
30mph at 3400
35-36mph at 3900-4K WOT

I also the ACME 13x12 .80 cup I have ends up having the same basic curve as the 13x13 OJ maybe 1mph and 100rpm difference on the 13x12. My chat with a few prop experts mad me realize you can hit a sweet spot with a prop and have the motor wake up, and it only takes a pitch or two to change the whole curve when that happens.

Anyway I can feel the RPM's are right sound and throttle response is like a whole different boat! I'm convinced this is the right prop for the boat and the RPM issue is resolved thanks for all the pointers everyone! Now I can even troll for Salmon without the socks out :)
 
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