Theoretically (and I'd expect it to be very close in practice too) the rpms for a given speed would be in direct proportion to the pitch. So if you were doing 55mph at 5000rpms with 12" pitch you'd pull about 5450rpms (5000 x 12/11) at the same speed with 11" pitch.
60 degrees static ignition timing?
Started by
_Bluejinx202_
, Dec 24 2012 07:06 PM
134 replies to this topic
#77
_Bluejinx202_
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Posted 10 February 2013 - 07:24 PM
Went out on the water today to do some prop testing. I haven't got a smaller pitch prop yet as I've been busy converting to a new prop shaft that will make prop tuning easier, and I thought I'd tr everything I have on hand properly before spending more $$$. Last time I went out I was tuning the ignition by feel (I know I'm not supposed to but that's what I was doing) I blew an alternator reg and ran out of battery so never got the ignition finished.
This morning I set reset he timing to 17 static, 36 total as new this was okay and would be safe to go and do some long high speed runs. So out I go and it felt doughy as so gave the dissy a knock around and it felt better, I told myself to "take it easy, don't blow this thing up, who knows what the timing is at this stage" It felt good, so I gave it more timing, ran it 3500 rpm for a while the got comfortable and floored it for a couple of minutes keeping an ear out for detonation (or a head gasket fail) came back all good. If it was going to blow it would have done it after that. Figured it was okay, changed some props, swapped some jets, changed a vac secondary spring, all going good, came back to the shed with a note pad full of changes and some ideas to change some stuff in hand and before I put it away, thought to check what the timing ended up at. 33static, 52total.... WTF!
Should the engine crank to start with that without fighting the starter, cos it sounds fine. Shouldn't the engine pop with 52 deg under full load? I know we've been down this road before, but its still baffling me and I'm not sure it won't take more timing yet...
This morning I set reset he timing to 17 static, 36 total as new this was okay and would be safe to go and do some long high speed runs. So out I go and it felt doughy as so gave the dissy a knock around and it felt better, I told myself to "take it easy, don't blow this thing up, who knows what the timing is at this stage" It felt good, so I gave it more timing, ran it 3500 rpm for a while the got comfortable and floored it for a couple of minutes keeping an ear out for detonation (or a head gasket fail) came back all good. If it was going to blow it would have done it after that. Figured it was okay, changed some props, swapped some jets, changed a vac secondary spring, all going good, came back to the shed with a note pad full of changes and some ideas to change some stuff in hand and before I put it away, thought to check what the timing ended up at. 33static, 52total.... WTF!
Should the engine crank to start with that without fighting the starter, cos it sounds fine. Shouldn't the engine pop with 52 deg under full load? I know we've been down this road before, but its still baffling me and I'm not sure it won't take more timing yet...
#78
_STRAIGHTLINEMICK_
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Posted 10 February 2013 - 09:36 PM
The engine will take more timing in a boat because it is not as loaded as in a car.It probably will not make any more power at 52 deg than at 40deg it will just feel more responsive at part throttle and when u stab the throttle.Its better to keep it at less than 40deg as bad things can happen with that much timing.
#79
_Bluejinx202_
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Posted 10 February 2013 - 09:57 PM
I better get to work and lock that spare dissy of mine up...
#80
_STRAIGHTLINEMICK_
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Posted 11 February 2013 - 07:44 PM
If you havnt already locked it up then i wouldnt do it ,I haven't seen any advantage in locking the diissy on anything but balls out drag engines.About 22 deg advance in the dissy all in by 3000rpm and set your initial to about 15 deg for a total of 37deg to make it easy to start and idle.I better get to work and lock that spare dissy of mine up...
#81
_Bluejinx202_
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Posted 11 February 2013 - 09:24 PM
If you havnt already locked it up then i wouldnt do it ,I haven't seen any advantage in locking the diissy on anything but balls out drag engines.About 22 deg advance in the dissy all in by 3000rpm and set your initial to about 15 deg for a total of 37deg to make it easy to start and idle.
Thing is... More timing seems to make it happier to start and idle. That 60 deg is still its sweet spot for idle. I've been on the phone earlier this arvo to a bloke that ran a wagott cam that's pretty similar in duration, he seems to think that he's ignition timing was pretty out there too (not quite as much as me but still unusually high) he thought that when trying a single carb, he had to increase timing from when it had the tripples. So theres hope for me yet. I just wanted to hear that someone had been down this road aswell and my figures made some sense, I'm just not used to working with these numbers....
#82
_STRAIGHTLINEMICK_
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Posted 12 February 2013 - 08:24 PM
OK your choice mate ,I don't know what else to say.
#83
_Bluejinx202_
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Posted 12 February 2013 - 10:19 PM
Mick, I know. I'm normally a great believer in getting the curve right, and I'm hearing you. Usually id be nodding my head agreeing with what you are saying. That said, I've never had/ heard of an engine being like this one.
#84
_oldjohnno_
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Posted 13 February 2013 - 06:48 AM
It'll run better with the ignition locked. If it kicks back against the starter just use a separate starter button so you can get it spinning over before switching on the ignition. I've done it before and it worked OK as a crutch on a badly configured engine.
But just remember that all this timing tomfoolery is just an attempt to cover up other problems that will still limit the engines performance. As you said earlier this very same engine made pretty reasonable HP with the 12 port head and EFI, and in that configuration wanted "normal" timing specs. Now, with the 9 port head and carb it just doesn't want to burn at all unless the fire is lit abnormally early. This is where you need to spend some time - try to get some heat into the engine, get the fuel broken up a bit more (annular carb if necessary) and maybe get some heat in into the manifold under the carb. I know this goes against normal practice but in this case I think it would pay. Maybe experiment with spacers/shear plates. Keep the squish clearance as low as possible. Give it a few more thou intake lash, maybe 2 or 3 more degrees of cam advance. Get it to burn and it'll make more power and want less advance.
But just remember that all this timing tomfoolery is just an attempt to cover up other problems that will still limit the engines performance. As you said earlier this very same engine made pretty reasonable HP with the 12 port head and EFI, and in that configuration wanted "normal" timing specs. Now, with the 9 port head and carb it just doesn't want to burn at all unless the fire is lit abnormally early. This is where you need to spend some time - try to get some heat into the engine, get the fuel broken up a bit more (annular carb if necessary) and maybe get some heat in into the manifold under the carb. I know this goes against normal practice but in this case I think it would pay. Maybe experiment with spacers/shear plates. Keep the squish clearance as low as possible. Give it a few more thou intake lash, maybe 2 or 3 more degrees of cam advance. Get it to burn and it'll make more power and want less advance.
#85
_Bluejinx202_
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Posted 13 February 2013 - 07:12 AM
I've got a couple of options... Rather than spending more money on an annular discharge carb. I could get a twelve port manifold and run the the other head, or try the single weber carb and manifold. I think the weber has a finer fuel mist and from what I've heard, my marine manifold is pretty good and most of my competition use them. The other thing I've heard of doing with a Holley is to run two sheets of steel or brass flywire under the carb squashed in between the manifold.
#86
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Posted 13 February 2013 - 02:59 PM
Just dropped off a dissy to get locked up. I didn't want to weld it up, that's why I got my dissy man to do it, so it can be unlocked as I hope not to have this engine running like this forever. He muttered something about there being something up with combustion chambers on the head. He wouldn't go into it because I think he doesn't want to second guess the guy that machined my head. But does anybody here know the theory behind what he was inkling at? It has been making me wonder as a few members here have hinted that the engine hasn't met it's potential by reading the Dyno figures. I think the Dyno was sort of a wasted exercise because it needed more timing than what the tuner at the time was willing to put into it, we cranked the timing up when we got the engine back home out of desperation for some sort of performance. I wrote a post at the time about the carb backfiring etc on the dyno. Wonder if it's been the head the whole time? I'm thinking of spending the money on a 12 port manifold and trying my 12 port head to dismiss this as a problem
#87
_oldjohnno_
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Posted 13 February 2013 - 06:19 PM
Just dropped off a dissy to get locked up. I didn't want to weld it up, that's why I got my dissy man to do it, so it can be unlocked as I hope not to have this engine running like this forever. He muttered something about there being something up with combustion chambers on the head. He wouldn't go into it because I think he doesn't want to second guess the guy that machined my head. But does anybody here know the theory behind what he was inkling at?
Yes, the chambers are too big for that silly bloody cam - you can do all sorts of things (like those I've mentioned in previous posts) to crutch it but it's never going to run all that well until you get a sensible cam in it. Or get the CR and the intake set up to work at the rpms that the cam would work at. If it's a bit over 11:1 static, its probably barely making 7:1 dynamic. An IVC of 87abdc isn't ever going to work well at only 6000rpm.
#88
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Posted 13 February 2013 - 08:24 PM
What intake and exhaust are u using mate.
#89
_Bluejinx202_
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Posted 13 February 2013 - 09:10 PM
Yes, the chambers are too big for that silly bloody cam - you can do all sorts of things (like those I've mentioned in previous posts) to crutch it but it's never going to run all that well until you get a sensible cam in it. Or get the CR and the intake set up to work at the rpms that the cam would work at. If it's a bit over 11:1 static, its probably barely making 7:1 dynamic. An IVC of 87abdc isn't ever going to work well at only 6000rpm.
Dynamic CR..... The penny drops.
#90
_Bluejinx202_
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Posted 13 February 2013 - 09:15 PM
What intake and exhaust are u using mate.
It's a 570 street avenger holley with secondary metering block on a brand new Aussie speed manifold, x2 headers to a straight out 3 inch outlet.
#91
_Bluejinx202_
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Posted 13 February 2013 - 09:19 PM
Dynamic CR..... The penny drops.
Why does it work with the injection though? Because that was an open chamber 12 port so even less static. Seeing as its all tuned and works pretty good like it was, should I leave it alone when I put it back together or should I change the cam and retune? Will the performance increase greatly?
#92
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Posted 13 February 2013 - 10:12 PM
Without seeing the head its difficult to see what is happening in that engine.Like old johnno said the timing advance is required to overcome a combination mismatch. The intake air speed with the injection manifold and 12 port head is much greater and will fill the cylinders much more at low /med rpms creating much higher dynamic cylinder pressures (dynamic cr) .Higher pressures require less ignition timing and lower dynamic cyl pressures (which you seem to have) need more advance . If this is the problem then either the intake air speed needs to be improved or use a cam with less .050 duration or trap some cylinder pressure in there by advancing the cam. The effect of the intake valve closing point on cylinder pressure can be seen by setting up lifters and rockers on one cylinder ,turn the engine over with the srarter and check cyl pressure as normal with a compression tester ,then advancing and retarding the cam and checking cyl pressure again.The cam setting with the highest pressure is the best cam timing for that cranking speed only and will not be the best cam timing at higher rpm .Understanding this concept will help you when advancing or retarding your cam for best spread of power with any given combination.
#93
_oldjohnno_
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Posted 14 February 2013 - 06:34 AM
Mick's onto it.
This is the "social" boat that needs to run a single carb, right? If this is the case you have two choices. You can keep the existing cam and work around it's limitations. You'll get it to run ok but it'll never be ideal. Or you could put a sensible cam in it and make it much easier to tune, and ultimately the performance will be better for the rpm range that you are talking about.
Either way, with the single carb you need to get some heat into the engine. I know I've mentioned this before but it's really really important with a single Holley in particular. When the engine is coolish, I've found hot single carb engines run like a dog down low, they don't like idling and they want eleventy billion degrees of advance. But get some heat into the chambers (and all it takes is a few seconds at full throttle) and they are a completely different engine. Idle speed goes up about 500rpm, and low rpms smooth right out. The amount of advance it wants goes back to normal and it'll want less jet too. So whatever cam you use, if you're going to use a single carb do whatever you have to do to get some heat into the head, and possibly get some under the plenum as well.
This is the "social" boat that needs to run a single carb, right? If this is the case you have two choices. You can keep the existing cam and work around it's limitations. You'll get it to run ok but it'll never be ideal. Or you could put a sensible cam in it and make it much easier to tune, and ultimately the performance will be better for the rpm range that you are talking about.
Either way, with the single carb you need to get some heat into the engine. I know I've mentioned this before but it's really really important with a single Holley in particular. When the engine is coolish, I've found hot single carb engines run like a dog down low, they don't like idling and they want eleventy billion degrees of advance. But get some heat into the chambers (and all it takes is a few seconds at full throttle) and they are a completely different engine. Idle speed goes up about 500rpm, and low rpms smooth right out. The amount of advance it wants goes back to normal and it'll want less jet too. So whatever cam you use, if you're going to use a single carb do whatever you have to do to get some heat into the head, and possibly get some under the plenum as well.
#94
_Bluejinx202_
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Posted 14 February 2013 - 10:30 AM
Okay, thanks guys. This has been really helpful and I appreciate the time... I'll lock the dissy and just use it as is till after easter then take it out.
I have the other engine (the one I engine dynoed) on a stand with the 250@50 comp cam leaning up against it, I'll re ring the engine, install the cam an put back in and hopefully that cam will up the compression back to more normal. While I'm at it, I'll change the exhaust and plug the water feeds that put water in the exhaust up high (that are supposed to keep engine bay temps down) and just let the headers get hot and therefore hopefully heat up the intake manifold. I'll put the engine with the big wade cam back together with its 12 port and injection and leave it for a while.
I have the other engine (the one I engine dynoed) on a stand with the 250@50 comp cam leaning up against it, I'll re ring the engine, install the cam an put back in and hopefully that cam will up the compression back to more normal. While I'm at it, I'll change the exhaust and plug the water feeds that put water in the exhaust up high (that are supposed to keep engine bay temps down) and just let the headers get hot and therefore hopefully heat up the intake manifold. I'll put the engine with the big wade cam back together with its 12 port and injection and leave it for a while.
#95
_oldjohnno_
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Posted 14 February 2013 - 03:30 PM
Okay, thanks guys. This has been really helpful and I appreciate the time... I'll lock the dissy and just use it as is till after easter then take it out.
While you're at it open the intake lash up to 0.026". It'd be good to advance the cam a few degrees too but I guess you probably don't want to go to that much trouble.
Edited by oldjohnno, 14 February 2013 - 03:31 PM.
#96
_Bluejinx202_
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Posted 14 February 2013 - 06:45 PM
Nah mate, adjusting cam timing is engine out job (for me anyway) and if it's coming out its getting the old bottom end back with the new cam.While you're at it open the intake lash up to 0.026". It'd be good to advance the cam a few degrees too but I guess you probably don't want to go to that much trouble.
I was just looking at the cam card and it is "int @50 atdc 55deg" am I right working out on the dyn comp calculator that I want to achieve just under 12:1 for pump 98?
#97
_oldjohnno_
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Posted 14 February 2013 - 06:57 PM
No, you need to use seat-to-seat or "advertised" timing. I'd imagine you'd want at least 13:1 for that thing.
#98
_Bluejinx202_
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Posted 11 March 2013 - 10:52 AM
Finally got in the water this long weekend, tried out the locked dissy. Seems pretty good, it's locked at 38 degrees and no detonation. Performance is ok with a consistant 55mph and good low torque. Progression off the idle to the mains seems a bit doughy so I'll change some pump cams and see where we end up. As said earlier, this engine isnt staying in but just got to get through till the winter now and especially the big regatta after easter
#99
_Bomber Watson_
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Posted 11 March 2013 - 06:11 PM
Just give up and send me your boat James 
You can keep the engine.....
Cheers.
#100
_STRAIGHTLINEMICK_
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Posted 11 March 2013 - 07:53 PM
Just give up and send me your boat James
You can keep the engine.....
Cheers.
get in line Bomber ,It has to go past here before it gets to you
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