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RPM too low?
I converted my .91 ASP 4 stroke to gas and getting 7200 rpm with 14x7 prop. The manual says RPM range from 2500 to 11500. Now I know 11500 is insane but what should I realistically expect it to be?
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Might also add that it runs good and transitions good, fires right up and im at 28btdc. Just curious where I stand with RPM
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First, what did the engine turn as a glo engine? Second, those are not noted for being powerhouse engines.
Seriously, glo performance would establish a base line performance for the engine. After conversion to gas, a slight loss in performance would be noted but it shouldn't be excessive. |
Originally Posted by AC2
(Post 12228290)
I converted my .91 ASP 4 stroke to gas and getting 7200 rpm with 14x7 prop. The manual says RPM range from 2500 to 11500. Now I know 11500 is insane but what should I realistically expect it to be?
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Originally Posted by Truckracer
(Post 12228307)
First, what did the engine turn as a glo engine? Second, those are not noted for being powerhouse engines.
Seriously, glo performance would establish a base line performance for the engine. After conversion to gas, a slight loss in performance would be noted but it shouldn't be excessive. |
Originally Posted by spaceworm
(Post 12228336)
What did you do to the engine connecting rod ends to convert it ? Thanks
You lost me here...sorry :) I guess my answer is nothing |
Found a guy running on glow: 9360 rpm now on a Master 14x6 so I am down a lil more than 2k from that. still far cry short of the 11.5k ASP states in manual so Im thinking its an inflated number
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First off that is to much prop for that engine, second a Master airscrew has less pitch than an APC of same pitch so that MA is more like a APC 14x4-14x5 prop. Going to gas from glow you will lose some power. I would try a APC 13x7 or a 13x8. The 13x8 on glow should be around 9,500 to 9,800.
You might try advancing the timing to see what it does. |
I tried the 13x8 and it netted me about 250 rpm more. Last night I checked my timing and I was at 30btc. Sorry for reporting wrong earlier. I moved it to 28btc and will check today.
I checked with one of the engine converters and he said with that prop it is a good rpm but he uses 20:1 and I have been using 40:1. I will also try the different gas ratios. I also received my rcxell tach so I will plug it in today. Before I was using an old school TH hand held tach that uses the photoeye compared to counting impulses from the ignition with the rcxell.... will see what happens :) |
I would check the cam timing. My experience with the Magnum/ASP four strokes is that the cam is often set wrong.
With the cam mark straight up or down, the engine will idle down - (tick like a clock), start easy, etc but not turn 9600 rpm with a 14 X 6. With the cam mark correctly aligned with the push rods, the engine will be lucky to idle below 2500 but will turn a 14 X 6 @ 9600. One way to double check your cam timing is to check the valve overlap position. Find top dead center on the compression stroke. Then turn the prop one full turn. One valve should be just opening and the other valve almost closed. The exact center of the valve overlap event (rocker arms parallel) should be around 5 degrees before top dead center. If one valve is closed at top dead center on the overlap stroke your cam is set wrong! |
w8ye, thank you for that information! :)
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Changed timing 28btdc, 13x8 prop 7200 rpm. It likes 30btdc better 4 tanks of gas burned already....I will try different fuel mixture before I open up the hood
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Originally Posted by w8ye
(Post 12228707)
I would check the cam timing. My experience with the Magnum/ASP four strokes is that the cam is often set wrong.
With the cam mark straight up or down, the engine will idle down - (tick like a clock), start easy, etc but not turn 9600 rpm with a 14 X 6. With the cam mark correctly aligned with the push rods, the enginer will be lucky to idle below 2500 but will turn a 14 X 6 @ 9600. One way to double check your cam timing is to check the valve overlap position. Find top dead center on the compression stroke. Then turn the prop one full turn. One valve should be just opening and the other valve almost closed. The exact center of the valve overlap event (rocker arms parallel) should be around 5 degrees before top dead center. If one valve is closed at top dead center on the overlap stroke your cam is set wrong! It looks like the overlap where both rocker arms are even happens at 5 degrees after TDC. On the compression stroke they are both closed, I turn prop and intake opens, exhaust opens, both are open at 5 BTDC but at 5 degrees after TDC the rocker arms are parallel. When both valves are closed there is quite a bit of play in the push rods. |
The valves should both have .002" - .004" clearance.
The mid point of the valve overlap event should be around 5 degrees before top dead center. Be sure you are turning the prop in the direction that the engine runs. The timing mark on the cam should be in alignment with the the lifters at top dead center. The mark can point exactly at the lifters or opposite. The cam turns half the speed lof the crankshaft. |
facing front of engine counterclockwise but I do not see a timing mark on the cam??
Thank you :) |
The timing mark is sometimes a dimple and sometimes a line.
If the timing is set correctly, there is a 50% chance that it is hidden behind the exhaust cam follower. |
Hi Did I read your post correct and your running a 40-1 mix. If so change that pronto to 20-1 there are no needle bearings in the rod on that engine and it will self destruct due to poor lubrication. Which also could be causeing a lower RPM.
Now as far as your cam timing you will need to pull the cam cover and the outside lifter to see the cam dot as Jim said if it is correct reassemble recheck the valve clearance and look elsewhere. As a rule you can retard the timing a little to gain more power to swing more prop but run lesser RPM's. Myself I set everything at 28 and forget it. |
Cyberwolf,
You caught that, good eye! I used that stuff from home depot pro-mix premium that says its good for 16:1 - 50:1 then just last night I was looking at ratios online and thought to myself, you big dummy!! I thought 40:1 was more oil to gas when just the opposite is true. I need a little less than two bottles per gallon not one. It is a 2.6oz bottle.....Will adjust pronto!!Thank you!!! :) Back to the timing mark on cam, it was a dimple hidden behind the pushrod that's why I could not see it last night when I got home from work. I'm going to leave it for now and keep the 28btdc and see what happens with just the gas ratio then try to dial it in more from there if I do not see a difference. |
BTW, its been a few short months since getting back into the hobby since 2005 so damn a lot of this stuff has not come back to me yet. I seriously recall when I first fired up the engine how clean the exhaust was which kind started my thinking last night to look at the mix ratio. I felt I should be getting more residue out the silencer.
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On gasoline the exhaust will be mostly dry smut.
But what comes out the crankcase vent will look like diesel engine crankcase oil that has a 100,000 miles on it. It will be black syrup. You should be running a 16 - 20 to one (16:1) ratio to not have a rod failure. |
Got it, will do, thank you!
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Originally Posted by w8ye
(Post 12230232)
On gasoline the exhaust will be mostly dry smut.
But what comes out the crankcase vent will look like diesel engine crankcase oil that has a 100,000 miles on it. It will be black syrup. You should be running a 16 - 20 to one (16:1) ratio to not have a rod failure. |
11,500 only means that you can put such a small prop on the engine that it will spin that fast and not blow up. Does not mean best power. Running on gas vs glow is a power penalty. Your 7000 range is probably right.
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Yes sir, like I said earlier that 11.5k is insane...very good point!! I think I'm good where I am. Now that Im back on track with my fuel ratio I may look at the timing but one thing I noticed is the engine is MUCH cooler.
So I backed off to 30tdc because its seems smoother, 14x7 still give me 7200, Engine runs cooler, 20:1 might play with it a little more or just leave as is...I feel much better about the heat drop and the gas ratio. 7200 on my Reliant should be good. Thanks guys!! |
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