engine timing with high compression

KNJL

New User
anyone have a suggestion on what to do with timing settings when increasing the compression. lets say you change an all fuel tractors compression from the original 3.75 to 1 up to a 9.47 to one. would you back off the timing from the factory setting due to the higher compression to prevent preignition ? anyone have insight on this subject. and no I do not have a dyno to test different settings. I was also told to run a race gas mix with the nonoxy fuel that I use, is this realy needed at 9.47 to 1 in your opinion ? thanks in advance for any comments on this.
 
I would guess that you should move the timing back about 5 degrees from what it could be. I have 9:1 pistons in my MH44, it runs best with about 10 degrees at idle and 25 at full RPM (1400). The maximum advance would be higher if the RPM's are.
 
If you run 110 turbo blue or VCP I would guess you would be OK with the timing is now. A lot of motors weather they have been messed with or not can not run on timing marks. As long as it dose not ping under load you are OK.
 
Our latest engine we use 108 110 gas. At right at 14 to 1 . Timing is set at tdc to start. Then 10 deg for every thousand. 30 at 3000. Never had on dyno. No PTO. But runs good enough to win every once in a while.
 

Compression ratio is just one aspect of combustion chamber pressure . Cam timing and port flow capacity are two other biggies.
The size and shape of the combustion chamber varies flame propagation characteristics. Is it a wedge head, open chamber or a two cylinder Deere with the spark plug way back where the piston rings should be?
Rpm? Octane ? Polished combustion chamber ? Mixture slightly rich or lean ?
 
DavidG is right on.detonation causes power loss,damage and pounding that the bearings no not need,more hp is enough extra strain.If you hear the ping,it is too late,robbing power way before that.Lugging increases need for more octane,slow burn qualities and less timing,more jet helps too.Good luck
 
Buick&deere is right. Forget anyhing you know about car engines. Compression ratio is a static figure derived from actual static dimensions of the cylinder/stroke/combustion chamber and deck height. Actual compression ratio changes throughout rpm range and is dependent on everything B%D said below. A car engine with 10:1 comp. ratio and peak hp at 5000rpm and peak torque at 4000 probably has a comp. ratio equal to 6:1 at 1500 rpm. Valve overlap in a cam made to perform best at 5000 is still the same at 1500 since now part of the intake/exhaust port still open changes the comp ratio. A tractor is cammed for torque. No need for valve overlap at 1500 rpm so if it has 9.47:1 static , it probably still has 8.5:1 at 1500. That, along with a piston dome/combustion chamber designed for low comp. and distillate fuel is why you need such high octane for what seems like a relatively low comp ratio. IMHO 98 +/- would be where you need to be. Blend prem pump with 110 to get it. I assume you are well aware of the stresses and consequences of same.
 
(quoted from post at 20:48:03 05/11/15) Buick&deere is right. Forget anyhing you know about car engines. Compression ratio is a static figure derived from actual static dimensions of the cylinder/stroke/combustion chamber and deck height. Actual compression ratio changes throughout rpm range and is dependent on everything B%D said below. A car engine with 10:1 comp. ratio and peak hp at 5000rpm and peak torque at 4000 probably has a comp. ratio equal to 6:1 at 1500 rpm. Valve overlap in a cam made to perform best at 5000 is still the same at 1500 since now part of the intake/exhaust port still open changes the comp ratio. A tractor is cammed for torque. No need for valve overlap at 1500 rpm so if it has 9.47:1 static , it probably still has 8.5:1 at 1500. That, along with a piston dome/combustion chamber designed for low comp. and distillate fuel is why you need such high octane for what seems like a relatively low comp ratio. IMHO 98 +/- would be where you need to be. Blend prem pump with 110 to get it. I assume you are well aware of the stresses and consequences of same.

Randy, do I know you, do you attend our pulls in Remus?
 


It should be noted that pre ignition or detonation is just that, a firing caused by something other than a spark event so spark lead should not be an issue. It could be a hot spot within the combustion chamber or insufficient octane for the compression ratio used.

Actually, since combustion heat increases as the timing is retarded, retarding the timing may be detrimental to controlling detonation.

Careful building of the combustion chamber and pistons can minimize the tendencies for detonation.

Mel
 
well it is all relative,---retarding from a way advanced to actual retarded is one thing,but going up from stock with out all the safety measures,not so much.Retarding slightly from a high stock setting is pretty much rule of thumb.
 
I wouldn't be surprised if we know each other. I live out 6 mi east of mt. p on M-20 and 1/2 mi south on Wise Rd. Havn't actually pulled at Remus but have "spectated" there. My e-mail is open.
 
Detonation and preignition are two distinctively different phenomenon. What you describe is preignition. Detonation occurs when spark event is
too advanced for the octane, compression or combustion chamber/piston design resulting in problematic msv
 
(quoted from post at 18:48:27 05/14/15) I wouldn't be surprised if we know each other. I live out 6 mi east of mt. p on M-20 and 1/2 mi south on Wise Rd. Havn't actually pulled at Remus but have "spectated" there. My e-mail is open.

Your email isn't open, mine is [email protected]
 

Yes, definitely Colder Plugs and the timing MUST be exact..

ANY Pre-Ignition WILL shatter the top rings...AND quickly Destroy the engine..

Ron.
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top