Looking for timing numbers...
 

I would like to see if anyone is willing to measure the port timing on their .46 engines. Nothing real specific, but a OS .46 and Magnum .46 come to mind. I'd like to compare the timing of these to my TT .46 pro. I'm not really looking at altering my TT's timing but I'd like to see how it compares to other .46 engines in terms of timing.

Based on Downunder's method, I have been measuring timing starting at TDC and working in normal crank rotation towards BDC noting the opening of the exhaust, transfer, and boost ports and also their closing points before TDC. Since I have a small collection, I dont have the resources to measure these myself. Any help would be appreciated. All I am really looking for is opening and closing points of all ports including the crank port.

Thanks guys..

-Tim

RE: Looking for timing numbers...
 

I guess I can start it off then but I'll limit it to only Schneurle ported RC engines with the exception of the ST G51. Mine is the CL version which uses different exhaust timing to the RC version which I believe opens at 74 BBDC compared to the CL version at 70 BBDC. Figures will be ordered as exhaust, transfer, (boost), crank open and crank closed. If the boost port is different then it'll be inside brackets so if there's nothing in brackets then boost is the same as transfer ports.

ST G51 (RC)... 74 60 43 40
ST S45 ringed (early round head)... 80 60 40 50
ST GS45... 74 57 (53) 43 45
OS 46VF... 71 60 37 56
Magnum XL46... 84 73 (63) 35 50
Rossi 45... 75 66 (64) 40 55

RE: Looking for timing numbers...
 

Thanks for posting that. Can you tell me how one determines based on timing numbers how to differentiate between an rpm screamer and a stump pulling engine? I can see a small trend between my fox 40 and my Traxxas 2.5 in regard to similarity of timing duration and knowing the 2.5 car engine can rev up a bit but I don't know exactly how to tell based on when the ports open/close and how it should behave rpm-wise without running it. I figure a longer blowdown would indicate higher rpm but I'm still a little lost with early exhaust opening vs. later opening, etc.

Thanks for schooling me. I'm trying to learn 20 years of experience in less than 20 years... LoL.

-Tim

RE: Looking for timing numbers...
 

That's a difficult question to answer because general wisdom has it that an engine with high exhaust timing and fairly long blow down is a screamer but if you look at the Rossi timings it's very average yet it's a much more powerful engine than others with similar timings. Based purely on timing numbers, the Magnum XL46 would appear to be far more of a screamer than the Rossi :). Stump pullers though are a bit easier to figure. Engines designed specifically for CL stunt come into that classification because they need to be able to swing quite large props at fairly low revs. Generally these will have the exhaust opening at around 65-70 BBDC and a blowdown somewhere in the 7-10 degree range. An engine designed specifically for 3D flying will also have similar timings.

With all that said, I'd be inclined to think that a screamer would likely have exhaust of around 80+ degrees and transfers giving about 20 degrees of blowdown. Nothing's written in stone though :).

RE: Looking for timing numbers...
 

As I understand it, if an engine already has a short blowdown period, it'd be a matter of adding material to the transfer ports (and consequently the boost port?) so they open later, right? Take my k&b for example; since it only has 7-10 degrees for blowdown, I'd have to add some material of some sort to the top of the transfer passage which would make it open later thus increasing the blowdown period. Would JB Weld work for this or would aluminum need to be added to accomish this?

It wouldn't be hard to decrease blowdown timing to increase torque but going the other way looks to be trickier.

RE: Looking for timing numbers...
 

I think that the intake timing (and crankshaft bore etc) is just as important as the exhaust timing for high revs. For high revs you need to get that fuel in and the intake can close later compared to an engine that operates at lower revs, it is all a compromise.

RE: Looking for timing numbers...
 

My auto shop teacher always said "the easier the engine can breathe, the more power it will make". Obviously if you change intake flow, you have to change the exhaust flow. Of course modifications need to be made to all port areas to keep the power increase linear (at least in my mind). I suppose if you open the exhaust port sooner, you would in effect increase the blowdown period since the blowdown period is the time between the exhaust opens and when the transfers open. I didn't think of this beforehand.

Another aspect I thought of is the conrod. Most car engines have knife edged conrods. I've noticed my aero engines dont have knife edged conrods. Would it compromise the strength of the conrod if I put a sharp knife edge to the conrod? I wouldn't need to remove a lot of material to do this but I didn't want to do it if the risk of breakage is high.

RE: Looking for timing numbers...
 

dont touch your engine. If you want more power and want to send it to me my engine guy and I can get you 1,000 more on larger props and up to 3,000 more on smaller props. My last Magnum 46 i can pull a APC 10x8 at 15,100 most 46 engines can only pull a 10x5 APC at that rpm. Each brand of engine is a little different. most we set to the same timing and get simular gains. The thing is all brands have different carb sizes, chamber sizes, crank timing and port sizes.

Take the super tiger 45 we can pull 18,500 on a APC 9x8 with a Black jett muffler. if has low transfers. we are finding for every 10mm of stroke you need around .050" blowdown. 20mm stroke = .100

RE: Looking for timing numbers...
 

If you want to pay shipping to and from, and do the work for free sure I'll send it to you. Otherwise you can share your secrets if you like and I'll do my own work. I have engines that serve little purpose to me so if I muck them up, I'm not out too much other than ordering replacement parts. I'm not an expert yet, but I think I can experiment a little and find out what works or doesnt. I've collected a chunk of information and I'll continue to.

The whole point of me doing what I'm doing is so I don't need to send my engines out to pay a small fortune for work I can do myself. I don't have the money to farm the work out.

RE: Looking for timing numbers...
 

I understand where you're coming from Sport. I started out a few decades ago with the same mindset and the one thing I've picked up is that the lessons learned are called "Intellectual Property" and they have value. (That's why folks want money to do it for you, to pay for their knowledge) I am personally glad I chose the route to learn it myself because I have fun doing these types of things. It's a form of pleasure for me. I get the feeling you are the same way. It's all about what you enjoy.

RE: Looking for timing numbers...
 

Ive come to believe that I shouldnt have to pay someone to do something for me that I am capable of doing myself. Some people work hard, experiment, buy special tools, etc to do a job. I respect them for wanting payment for a service, however I'm willing to hold out, ask questions to those willing to answer them and learn for myself. I have no intention of making a business out of it, nor do I have the intention of doing modifications for anyone else. This is purely for my own enrichment. Besides that, in this economy, I just dont have the extra money laying around that I'd like.

I enjoy learning. Engines fascinate me and being that I didnt have as good of knowledge of the inner workings as I would like, I ask questions to better understand and perhaps in the end be able to make my own changes (and mistakes, I'm sure) without destroying something. Worst case scenario, I buy new parts. I wouldn't experiment on something I couldnt get parts for unless its already worn out and is hopeless to find parts for.

Someday I'll have a perfect understanding of everything, and who knows... maybe I might best someone all on my own. If that were to be the case, I personally, would share my findings to help someone else out and not expect any monetary gains in return. Thats just the way I am. There has to be something for free in this "free" country of ours.

RE: Looking for timing numbers...
 

lol I never asked for money and would do it for free but you would have to pay for shipping.

RE: Looking for timing numbers...
 

After I posted that my phone croaked and I didnt have a computer handy so I couldn't edit my post... I just got home now..

I was going to add to my last post that the last time someone put an offer out there like that, they wanted to charge me $100 + shipping both directions. I just dont have much money right now since my wife started a new job so I'm being cheap. I have modified my own engines a few years ago but had no real way of testing the before and after (car engines) but what I did made a positive difference.. I was going to apply what I learned and did on those car engines to something else only getting more into timing of the ports. If its possible to make the poor-mans 4-stroke act more like a "60" sized 2-stroke I'd be happy.

Is the Magnum you re-worked have a Chrome/Brass sleeve or Nickel/Brass? I'd like to get more rpm from my TT .46 Pro but with the nickel sleeve, I didnt want to risk the nickel peeling. My TT .46 on a red Jett pipe and 5%nitro/20%castor I get 16,500rpm on a 9x7, 15,500rpm on a 10x5 and 14,700rpm on a 10x6 all APC props. Its on an Outrigger Airboat that needs to go fast. I was going to check the crank timing and open it up a little but thats it. I didnt want to mess with a nickel sleeve.

I'm gonna mess with this K&B .65 since I have 2 of them and access to 5 or 6 more all unrun. I am also somewhat interested in investigating whether or not I can get one of these things to turn to turn 13,000rpm and be happy doing it. It spins a 13x6 apc at 10,200rpm which my ST 90 spins at 12,600rpm. I'd love to see the K&B do what the ST can. Everyone would laugh at me if I ever flew it in the plane but hey.. why not?

RE: Looking for timing numbers...
 

One way to alter the timing without touching the liner is to file the piston edge across the width of the port at around a 45 degree angle but only to the extent you'd normally grind the top edge of the port in the liner.

RE: Looking for timing numbers...
 

"An engine designed specifically for 3D flying will also have similar timings." Downunder


Speaking of which, I have a NIB Rossi .45 3D of two or three years vintage, IIRC. I wonder how well it performs as a 3D engine? Anyone?

I'm thinking of putting it in a Harrier 46 ARF, if someone doesn't buy it from me first.


Ed Cregger

RE: Looking for timing numbers...
 

An even better way i to shim the sleeve and have the top of the sleeve turned down the same amount.

we have done many plated sleeves with no issues. just use a diamond cutter and go slow. trying to cut to fast will cause bigger micro fractures. once cut then polish slowly again with 1000-1800 grit paper.

Fot your TT need to open the carb up to .320-.340 (slowly open up and recheck to make sure can close off and kill engine) dont mess with crank timing the TT is close. add JB weld or simular epoxy to front half of crank set up to dry so it pools at a 45 degree angle. Fot the crank opening just square off the back corners. Then put a two angle job on the crank entry going rearward. install crank with out carb and look to see if the case needs some grinding to match the crank hole.
Now raise crank timing till you have .100 difference in blowby. should pick up an easy 1,000 with Jett muffler.

RE: Looking for timing numbers...
 

I've done plated sleeves too, but they were chrome plated brass sleeves. A true ABC sleeve is only plated on the inside of the bore. A Nickel plated sleeve like in my TT is plated inside and outside. This is where I got concerned. If you say it can be done without peeling, so be it. I take your word for it.

The carb is no problem, and I've stuffed cranks before.. I need a little clarification regarding the crank timing/port. Squaring off the back corners of the crank opening - in the crankcase or the crankshaft? Two angle job on the crank - crankshaft intake port?

You also say dont mess with crank timing because its close but at the end you say raise crank timing til you have .100 difference in blowby. I remember seeing you say something about .100 transfers on your magnum however I dont exactly know what you mean by that. .100" difference in height between exhaust and transfers? Measurements in degrees of crank rotation is easier for me but I didnt know exactly what you meant...

Thanks for the info.
-Tim

RE: Looking for timing numbers...
 

Yes sorry about that. sometimes i know what i want to say and have it all in my head and cant type as fast as my thoughts.

Exhaust timing is what i meant not crank timing.
Square off rear corners of the crank. think of the carbexit to crank entry as a port. the rear section is the port floor per say. squaring off the corners effectively (sp) widens the floor (helps with the short side radius air flow).

2 angle.. do you know what a 3 angle valve job is? if so use same idea only use two on the crank passage going down the crank. i will see if i can come up with some pictures this weekend. i will have to take apart some engines to show ya.

RE: Looking for timing numbers...
 

Pics would be cool but if you can't swing it, no biggie. I think I know what you mean. I did a 3 angle valve job and lapping back in high school.

Whats the deal win the .100 transfers? What did you mean by that?

RE: Looking for timing numbers...
 

if you measure down from a set point on top of sleeve to where the piston just closes the transfer and the distance from there to where the exhaust opens up we find that the .100 per every 20mm of stroke seems to work very well with the Jett pipes.

So with that if you need 180 degrees of exhaust timing to get the engine to run best on the Pipe then take the transfers up to the number above if not there. if already past that like some engines are then you wil have to look at lowering the sleeve in the case and shimming the head. I will have to get the numbers on the Squish for the TT. by the way we set up all our engines to run on 5% since its will save a little bit over 15%.

RE: Looking for timing numbers...
 

Thanks for clarifying that. I got it now for sure.

I run all of my engines on 5% nitro anyway. The Super Tiger S90K I have will run on FAI fuel but I lose 600-1000rpm on a given day. The tuning window is perfect on 5% too.

I am going to run the TT tomorrow on my airboat and see how it does. I'll tear it down over the winter but I'll at least time it in the next week or so. I will post its numbers when I time it.

RE: Looking for timing numbers...
 

Alright Airraptor. I finally measured my TT .46 timing. I dont know the combustion chamber size, I dont have any small syringes to measure the bowl in the head button but the squish band I get is .21mm. Top of liner to top of piston at TDC is 4.12mm. Bottom of head button to bottom of head shim on head is 3.91mm.

Bore is supposed to be 21.8mm and Stroke 20.0mm

My port timings are as follows
Exhaust is open at 75, closed at 76
Transfer open 61, closed 62
Boost is open at 59, closed at 60
Crank is open at 37 and closed at 45
Blowdown is 14°

Transfer port just closed, top of piston to top of liner is 59°BBDC, or .804". Exhaust port just opening is 75°BBDC or .717" So by rights I should raise my liner .091" to bridge the gap or raise the top of the exhaust port? I'd think raising the top of the exhaust would be easier. Raising the exhaust to .704" would give me +2° exhaust duration or open at 77°BBDC.

I tried to measure this as carefully as possible.. give me your input.

RE: Looking for timing numbers...
 

This engine will turn a 9x7 APC at 16,700rpm on 5% nitro. I'd like to keep the mods to complement using just 5% nitro. I want to get another gallon through it so its good and well broke in (its at roughly 1 gallon right now) before I make any modifications. To start with, I was going to "stuff the crank" with some sort of adhesive to "ramp" the crank port. After curing and testing I was going to square up the floor of the crank port. The port in the crank itself looks pretty good so I think I'll square up the floor of the crank port area in the block. My next mod was going to be scalloping the crank - the counterweight as well as the center port.

I'm going to buy a puller to remove the prop driver since the crank will have to come out a time or two. After the above is done providing its all worth doing, I'll make adjustments to the ports in the sleeve if I dont see the RPM I'm looking for.


I know it probably wont do it, but I wouldnt mind seeing it turn a 10x6 at 16,000. I think right now it'll turn it at 14,800. a 10x5 will turn at 15,500rpm. I need to keep it above 15,000rpm to get it on the pipe.

Airraptor - does this sound like a decent plan or...?

RE: Looking for timing numbers...
 

Another question... What is a decent general idea of timing numbers to take full advantage of a full wave tuned pipe?

RE: Looking for timing numbers...
 

Generally 180+ on exhaust timing is pipe timing.

What is the measurement where the exhaust port close?
How wide is the exhaust port at the top?
How big is crank hole?
How big is carb? IE (.300 - .330) i think those are .310 on the TT
How is your crank measured? from BDC or TDC. I usually just got of when i can see light coming thru crank and use the back cover screw hole as a reference. The crank starts to open when near the screw hole at the 7 o-clock position and closes around the screw hole at 1 o-clock for around 180 degrees total. normally you want it to open around 40-50 degrees. I will dig in my boxes and get the numbers i have for you ok.


Oh year i think 16,000 is with in reach. on a jett pipe.