Looking for a tuner in Florida
 

I have a 1996 27 powerquest w/ a built 502. I was running 61 gps before the rust in the head opened up water into the cyl and needed a rebuild. I spent a lot of money and put awesome Merlin heads w/ big intake vlvs, eng bored .060 over, big cam ,cmi headers sniper throttle body inj.etc and only run 62 at 5100 rpms.I expected a 70mph boat. Since I had one guy make the heads, one guy do the machine work, another guy do the build up and I installed the eng and put on the sniper there is not one guy I can take it back to and say WTF it is no faster than my stock eng.

What I am looking for is a shop in Florida, preferably near Tampa that knows how to make these things sing and has a prop dyno or can water test and see if we can find the weak link that is keeping this thing down on power.

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heads

Can’t help w a tuner down there but curious on a few things.

what is your fotal timing ? Not guessed nor assumed, but actual ?

What is your a/f ratio at max rpm ?

Does your fuel psi stay at proper spec all way to top rpm on the water (not trailer) ?

what specs does this big cam have ?

are your plugs gapped at typical .035 or so and not the dumb .055+ DUI suggests ?

1 I know I am a bit retarded not personally but I am at 29 deg. I was w/ a friend last week out to set it at 32 when I spun the hub in my propeller.
2 I can't remember what I saw on the screen that plugs into the sniper, it was 11.8 at max rpm, 13.5 cruise,14 idle
3 I have a fuel press gauge just before sniper and holds at 60 at all rpm
4 I know .055 was ridiculous, I think that # came from their marketing dept, I am at .045

What was done to the merlin heads that made them "awesome'/ Out of the box they are virtually identical to stock rect ports at just over 300 cfm intake flow at .600/ 200 cfm ex at .600, unported they offer no real performance gain. Ported, thats a different story. what was your previous cyl heads, intake etc compared to what you now have, what are your cam specs/
what octane is lowest you ever run? whats your CALCULATED /ACTUAL COMPRESSION? IF you dont no real compression (most guys think its higher than actually is), what kinda dome is on your pistons, how far are they in the block?
Stan Weiss' - Cylinder Head Flow Data at 28 Inches of Water -- DFW / FLW Flow Files for use with Engine Simulation Software

I think the merlin heads are your problem,,they suck,even if work them over,thin casting around the exhaust port,,work them to much and a few years down the rode,they spring a leak.salt water makes it happen way faster.

what cam are you running?

Forgot to add, the DUI internal cap coil HEI distributors need a better power source and thicker wire than the OE Merc purple wire. Do a search. Several peeps spell it out with 10-12 gauge wire and relay.

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SB.
running 12g wire right from bat thru relay to distrib
I purchased the heads new from Ron Sporl Performance, Manley Inconel ex Manley intake, can't remember the size but next bigger than 2.25 runners ported pockets bored out to bring comp down to 9.5 pistons were down .010 in block
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ignition timing may be holding you back, do you run premium? similar 502s to yours made best hp at 35, 36 dgrees of timing on my dyno with iron heads, a factory 500 mefi runs 35.9 timing on top BUT it does have a knock sensor. If I dyno a 9-1 iron headed engine at 32 vs 34, 35, I will see about a 20 hp drop at 32 sometimes, at 29, im sure its more BUT if your running 87 and since you dont have a knock sensor, I wouldnt get too carried away with total timing. Id also say to install afr bungs in your headers and see what your afr is at wot, Smitty

See post #2. He has bungholios with sensors installed in both.
Hmmm, looks like GM dual plane too.

cams installed to advanced,should be around 109-110icl

polishing chamber is okay,,really need to see that exhaust port,that will tell if your gonna make some hp,,plus,that cam doesn't have near enough spred,its not a street car,8-10° will be the norm w/ good exhaust ports,,merlin probably needs 12-14°.run it for the season then change some parts.

MORE INFO: I am running the stock gm intake manifold dual plane but cut down the center divider about half way. Icon forged pistons, run 93 octane, long rod eng. sniper keeps wot f/a ratio at 11.8 which I can set to whatever I want so that helps against detonation but I do not have knock sensors or electronic timing reduction. I set my timing at 29 to be safe for break in and I just havent had the balls to bump it up to 33/34. I would like to do that w/ an experienced tuner either on water or prop dyno. My overhaul had a lot of Chiefs but no 1 person in charge. I should have just take the boat to a reputable guy and dropped it off and said call me when its perfect. I really did respect what Ron Sporl told me to do regarding the heads and cam selection and timing pos, now weather or not my builder knew what he was doing and actually set it to 104/106 I don't know. I now Stuphen 30 has been on this forum quite a bit and maybe you are right about 109/110. Not sure if this makes sense but I remember Ron saying the pistons I had would give me too much comp so he ground open the pocket and I think he set the cam to lower the running comp to give me about 9.5/1, does that make any sense?
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Are you driving the boat like worldwide prestige (trim down) buy any chance ? :evilb::bunnydance:

I used to drag race my Action Marine then my STV tunnel v which did 104 on a good day, I'm no stranger to what it takes to go fast but I have always been an outboard guy. I trim up till I feel it start to ventilate then bump down till I feel it catch. At 62 mph the boat is trying to get on the step, the bow oscillates up and down, I need another 5 mph to get her on top and fly. Maybe bumping my timing up will give it to me but now I need to find another prop and debating between a 3 or 4 blade. I don't want to go any slower and I am not having any problems planing or staying there at slow cruise so I am leaning toward 3. The boat weighs about 5200lbs

Well, your timing is very conservative. A/F ratio not too far off from fine.
I have never run any bbc nor sbs with less than 32-34 degrees unless it was getting a shot of funny gas. :) So, I'm not sure how much power you are losing, but I know low and midrange timing being off as little as 4-6 degrees will make an engine accelerate a lot slower than it does with more. Fun vs blah blah. Again, I never have total timing at a lesser value, so can't answer for there. I would assume (uh oh) would make it lethargic there too.

I am going to try to get out in the boat next week. I have a solid hub 21p mirage and will set my timing to 33 and record what I have for a/f ratio at mid and wide open, note speed, rpm and outside air temp, I am at sea level. I am running a 150 thermostat. I am using the stock pointer on the timing chain cover and installed timing tape on the dampner. My piston part # is Icon 808-064

It will be a night and day difference when you put some timing in it...

Now you are just getting me exited. I am looking for a 23p prop as I mentioned earlier I spun the rubber hub stiletto 23. If I am looking at a mirage is the 27 powerquest a boat that would benefit from the additional cup of the M+ or should I be looking at a vengeance. I noticed the vengeance is only 13.5 in dia, is that too small for a single eng 27' at 5200lbs

That is small block small boat prop diameter.

Here’s a discussion amongst other 27ft Powerquest owners and what they are running for power and props:
https://www.offshoreonly.com/forums/...rop-270-a.html

My opinion... I'd get it to 12.4 AFR and bump the timing to 32° min. Do AFR first with plug checks and then increase timing 2° at a time. I ran 36° with my 9.7:1 steel Merlin headed engines. (fully wedged and ported) Out of the box the heads are a little better than stock, the split on the cam should be 8°-10° as S30 mentioned. I do believe you have a nice little build but it needs a little tweeking. I don't believe you will/would have ever seen more than few MPH going from a built 502 to another modest built 502.

Edit, i was wrong about prev motor. Doh!
Here is the op’s previous 502 build:

https://www.offshoreonly.com/forums/...stributor.html

1) With that much duration @050 and 9.5:1 I definitely agree with 6 to 8 degrees advanced on the cam (106 ICL). If you install it closer to "straight up" you'll want to prop it for 5500-5600 rpm. You DO need to KNOW where your cam is installed. And you CANT KNOW unless the guy who installed it used a properly calibrated degree wheel.

2) what head gasket thickness are you running? If your pistons are .010" below deck, then you would be best served with .030"-.035" compressed height on the head gaskets because that puts you in the optimum "quench clearance" zone (.040-.045 is best for a 502, .036 to .040 is best for a 454). The reason this is important is because squish turbulence really suppresses detonation and let's you run higher compression and combustion pressures before you have to worry about detonation. If you have the typical. 039 thick Fel Pro Marine gaskets, then that puts you at .049 which is still well within the efficient squish zone.

3) BBC combustion chamber on pump gas with flat top or low dome pistons is baselined for most effective power production at 36 degrees. But for that to happen a lot of stuff has to match up.
Let's say you have a 7.5:1 BBC and 98 octane gas. The low compression ratio keeps cylinder pressures low during combustion. Advancing the timing gives the flame more time to burn, bringing the pressures up and delivering more torque/power. The high octane burns slower than low octane, so it needs lit sooner as well. This bad combination may need to see as much as 40-42 degrees advance before the power peaks. But it is due to a bad combination.

A 9.5:1 502 (like it has been said, you have to know the bore diameter, piston to deck measurement. piston volume factor in Cc, combustion chamber Cc as measured after polishing, head gasket compressed thickness, fire ring diameter, actual stroke (some regrind cranks can be offset ground for a tiny increase in stroke). Knowing all of that is the only way to know the compression ratio)- anyhow a 9.5:1 502 with .049 quench clearance and a 240/244 cam at 106 ish ICL should honestly handle the full 36 degrees of advance on 91 octane, and MAYBE 89 octane.

A/F Ratio?
E10 (gasoline w 10% ethanol) best power between 12.0 and 12.7
100% gas. between 12.5 and 13.2
I would set my ECU to 12.2 WOT.

I would leave a lower pitch prop on it until you are making enough power to spin it over 5600. I'm guessing your setup will make best power at 5400 (unless I am overestimating the flow of your intake man).

Use brand new plugs. Don't run it intentionally rich, as this will mess w your plug readings.
if you want to creep up on the timing, you need fresh white insulators on the plugs and dont soot them up by running too rich.
Run it out hard, pull the stick back.
Shut it down. Pull whatever plug is easiest to yank.
Look at the plug insulator and see if you can detect any metallic speckling - this will be your indication of detonation.
If you dont see speckling, and youre getting more power with more ignition advance. Then keep adding advance. If you get past 36 degrees and move to 38 degrees and you don't get detonation then you know you're sitting pretty.
Next step is to drop octane (temporary tank) and retry. You may discover that you can run 89 octane at 38 degrees.
So THEN you have your parameters.
Whatever octane you can run at 36 degrees is your sweet spot.

my bullet custom grind 238/245 at .050 has a an icl of 110.have done many 454's and 502's at 109-110 and all the motors rip.but if you want the motor to peter out around 5000-5200 all the power to you.merc uses 106 so their motors don't rev up,built in rev limiter.

From s30

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Thanks everyone, I am waiting on a couple of more props to come in and a nice day and off from work and a friend to go out and help, may be a while but I will post results.

I finally took the Powerquest out today to some testing and was not happy. The first part was to advance my timing from 29 to whatever she ran the best and back it off a little. I thought I would see the biggest improvement w/ my first few degrees but got nothing. Calm winds, oil temp stable I mad a run w/ a 23" 3 blade saw 60 mph gps and 5000 on sniper display. I bumped the timing to 32, made same run, no change on either. I did not want to advance it any more. Midrange a/f ratio is 12.8 Full throttle is 12.4. I did not do a shutdown and read plugs, I just did not think about it at the time. The second part was to play w/ the 5 props I had. I changed to a 21 3 blade mirage. 5350 and 61.5 mph. I had some 4 blade 23's revolution, it was just too much prop, dropped to 58.5. I was expecting to see improvement up to about 36 degrees but will keep it at 32 for now. I really need to go out w/ an experienced tuner who can look over my setup and advise me on what I am overlooking. A very disappointing day. Did a compression check in the driveway after an hour of the flush. 6 cyl's were 170 1 was 179, one was 161. I checked the 161 again same result. Plugs were very white from the 5 min at idle and 14 afr. gaps at .045 run by the DUI distrib. w/ dedicated 12v 12 gauge wire direct from bat thru relay. Willing to drive most of Florida to a reputable performance shop if anyone knows anybody. Thanks everyone for the prior input.