Flex

Not a big issue. Only heat you need to worry about is heat from flex being too short, carb too lean and lugging the engine below the intended RPM’s.
Im new to the open/uas scene and the majority of the time ill be on tracks that range between 1/10 to 1/8 mile stock bore and stroke sudam with buller daul carbs on alcohol whats ideal rpm and do you think 9 3/4” flex is a good initial starting point? And is it more efficient to go off of head temp or egt and depending on which is better what temperature do you suggest to maintain
 
9 1/2” has been my baseline for the CRE9 and KB06 but it really depends on the desired RPM and clutch engagement. EGT is far more valuable than CHT on a Sudam. If the carbs are kept rich there should be no reason to be running hotter than 1100F. Keep in mind that EGT can read hot when lean AND rich, and same goes for low EGT. It’s not a one way street. @alvin l nunley can elaborate on this further with EGT.
 

rainman

Premium User
KB06, on 131 stroker Sudam I am runnning close to 9 3/4 flex, but you can Buller recommends between 8 5/8 and 9 1/2. CHT stable between 280 and 310 degrees, maximum 340. EGT between 650 to 800 range, maximum 900. Obviously a stock 125 Sudam might be more forgiving than my stroker but I would be careful because temps are the great enemy of these engines. Run recessed gap plugs, clutch engagement between 10,000 and 10,500 rpms, and I say this because every engine is different from what i have learned through the years, you'll never have 2 engines even built the same with the same top rpms, that for example on my 131 the maximum at short ovals is around 14,800 rpms, but on long oes I am actually faster running a little under 14,000 rpms on lower gear ratios. 8oz of oil per gallon, Blendzall green, Klotz Super Techniplate, Red Line, any of these are pretty good, and make sure you flush the engine with non ethanol gas and a 12 to 1 mix of Marvel Mistery oil after your day is over or methanol will ruin your engine and before the engine the carbs too. Make sure your squish band is where it need to be too, and don't go too far on timing because too much advance will burn pistons right away.
 
KB06, on 131 stroker Sudam I am runnning close to 9 3/4 flex, but you can Buller recommends between 8 5/8 and 9 1/2. CHT stable between 280 and 310 degrees, maximum 340. EGT between 650 to 800 range, maximum 900. Obviously a stock 125 Sudam might be more forgiving than my stroker but I would be careful because temps are the great enemy of these engines. Run recessed gap plugs, clutch engagement between 10,000 and 10,500 rpms, and I say this because every engine is different from what i have learned through the years, you'll never have 2 engines even built the same with the same top rpms, that for example on my 131 the maximum at short ovals is around 14,800 rpms, but on long oes I am actually faster running a little under 14,000 rpms on lower gear ratios. 8oz of oil per gallon, Blendzall green, Klotz Super Techniplate, Red Line, any of these are pretty good, and make sure you flush the engine with non ethanol gas and a 12 to 1 mix of Marvel Mistery oil after your day is over or methanol will ruin your engine and before the engine the carbs too. Make sure your squish band is where it need to be too, and don't go too far on timing because too much advance will burn pistons right away.
Thanks rainman if you dont mind i May message you with more questions if you do not mind!
 

alvin l nunley

Premium User
Rainman, have you ever tried to go with higher EGT temps? Boring that engine raised the compression ratio, have you ever checked the cc's on the combustion chamber?
The reason I ask is because I've never seen such low EGT temps. There could be other reasons they're low other than rich or lean, such as, placement of the EGT probe, compression ratio, spark plug, fuel, timing etc. etc.
Many people, having run the CHT, have a fear of running the EGT temp too high. With the EGT you want to run as high a temp as possible. Maybe just under that point, for safety sake. When the temperature gets too high, the fuel will start detonating, and the temperature will go down. This happens long before the engine will stick. Some people make the mistake of leaning the engine down father when they see the temp drop. Actually, if you see the temp drop, you should first check to see if the engine is lean, open the high-speed. That goes for the low-speed too.
 

rainman

Premium User
Rainman, have you ever tried to go with higher EGT temps? Boring that engine raised the compression ratio, have you ever checked the cc's on the combustion chamber?
The reason I ask is because I've never seen such low EGT temps. There could be other reasons they're low other than rich or lean, such as, placement of the EGT probe, compression ratio, spark plug, fuel, timing etc. etc.
Many people, having run the CHT, have a fear of running the EGT temp too high. With the EGT you want to run as high a temp as possible. Maybe just under that point, for safety sake. When the temperature gets too high, the fuel will start detonating, and the temperature will go down. This happens long before the engine will stick. Some people make the mistake of leaning the engine down father when they see the temp drop. Actually, if you see the temp drop, you should first check to see if the engine is lean, open the high-speed. That goes for the low-speed too.
Thanks, Al. Most of this info is from Buller and he builds Sudam and seems to work for me. I have rebuilt it too from top to bottom when I had access to my friends crank press jig in VA and the only thing I have really changed from Buller's recommendations or setup has been a little less timing advance or more flex when running too hot which is the biggest issue with my stroker Sudam. As I said any particular engine (especially open or highly modified engines) is different and mine seems to work better tbe wsy I am running it now. I did try many things before and I paid the price in pistons and other issues. Other than that I play more with other engines I build myself but if I pay a good builder I usualmy follow his advice unless I have a big problem or issue at the track. I am not usi g the EGT at this point anymore. I do know it gives you a much more accurate info than the CHT but after some playing arou d it works as good as it can at 400 lbs with me and the light young drivers I could seat on the kart are too lazy to sit them there so the old heavy guy will stay in the seat for now. By the way my engine is regular bore for a Sudam. It is a stroker as most 131 Sudams out there on UAS. Of course head ccs and squish are where they should be and I always check that even after it comes from him just in case. Buller had to rebuild that chamber and for me after I blew the lower rod bearing and made a mess. He did an awesome job. I also have more meat in the crank than older original engines to prevent cracks since it is a stroker and with the pin set closer to the edge some tend to fail there. Second piston size on new liner a d a bunch of new stuff with few races. Only old thing on it again is the driver.
 
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