Went from a slant plug to a straight AND....

Donavan321

Donavan321

New Member
I pulled the 66cc slanthead off of my engine and added a 66cc straght plug head, I love the look a lot better..BUT it seems like the bike is a tad bit slower? It's still fast..I'm just not sure so I think I lost speed from 43mph to a little over 35....but like I said sometimes it just seems I need to give it time to reach true WOT. my slant head looks exactly the same inside. I know the slanted plug was designed to clear frames that have clearing issues and some heads have a design to them that allows for better compression. This isn't the case here...maybe I think I'm just losing power? I may be adding a speed carburetor as well as a performance air filter. I AM running a speed demon exhaust. I think I'm just imagining a loss in speed because the motor looks like the 49cc motors with the straight plugs lol...runs great though! Happy riding!
 
if you think you're losing power make sure your head gasket isn't leaking and the head's properly torqued. i've always had faster bikes with the straight plug.
 
My theory on it is this: due to the domed top pistons, the straight plug heads put the plug much closer to the piston, therefore the combustion chamber needed to be larger. The slant heats put the plug on the side of the piston dome, allowing for more clearance while being able to shrink the combustion chamber, thereby increasing compression..






But that's 2 cents from a non-stroke guy. :D
 
A lot of the older strait fire heads where as high comp. as the angle fire heads, but a lot of the new ones are suuuuuuper low comp:

4E398897-C24C-43B7-8DC4-A06817B7A20A-169-000000272BCA4157.jpg
 
Okay, thanks for all of the input guys! I do prefer the look of the striaght plug, I like that taller head... now, when I look at both of my heads, the insides look exactly the same...the only difference is the slant head has the angled plug...VISUAL differences....the insides of the heads look exactly the same..which is weird...same number of threads, etc. I did notice a power loss...could reach 44 mph with slant plug, added straight and could barely do 30-35. Is there any way to get better compression with the straight plug head? Any kind of shaving or grinding? Let me know, I apprectiate all of the feedback guys!
 
You can lap/deck the head to remove material. But to be honest, if you want speed, just put the slant head back on. It's cheaper. :D
 
Yeah, the cheap way is usually the easiest to go! I'm going to try the head on my new motor when I get the kit in the mail. I'm ordering it tomorrow hopefully. I really like that style with the straight plug, do I need to be going 45 mph? No, not really but 25/30 mph can be a little boring after awhile, lol. I have considered maybe running the straight plug....all stock doing about 25/30 or whatever and then just adding performance air filter, speed carb, etc. I usually stay running with the 44t sprocket and then run #41 roller chain. Have any cheap ideas for getting a little more power without severe engine mods, etc? I'm trying to reach that happy medium area. good looks(straight plug) and decent performance..like I said I'm going to reattempt it on my new motor kit(probably same results but you never know!) I think I also read somewhere on the forum here, that the straight plugs give a more complete burn? I know the slants were designed mostly to clear frames that had clearence issues with the regular head. BUT, alot of people are saying the slants have higher compression, BUT the plugs are slanted ...yet when I look at the head the electrode is still pretty close if not in the middle of the head? I also read that the older straight plug heads have the same compression as the slants and that the "newer" ones have less. Is it possible I can purchase an "older" straight plug head somewhere?
 
dodge dude94 said:
My theory on it is this: due to the domed top pistons, the straight plug heads put the plug much closer to the piston, therefore the combustion chamber needed to be larger. The slant heats put the plug on the side of the piston dome, allowing for more clearance while being able to shrink the combustion chamber, thereby increasing compression..






But that's 2 cents from a non-stroke guy. :D
Click to expand...

Very helpful, thanks! I wish that they'd make the straight heads have the same compression! Just so it wouldnt matter if the head was straight or slanted.. it would be the same for both heads and then that way if you were building on a low clearance bike, the slanthead would JUST be for CLEARENCE..while offering the same compression as a straight plug...Facepalm..
 
Donavan321 said:
Very helpful, thanks! I wish that they'd make the straight heads have the same compression! Just so it wouldnt matter if the head was straight or slanted.. it would be the same for both heads and then that way if you were building on a low clearance bike, the slanthead would JUST be for CLEARENCE..while offering the same compression as a straight plug...Facepalm..
Click to expand...

Go to treatland.tv, check out the parts section for Puch they have the hihi 50cc heads straight plug and the 70cc hi hi heads.
Youmight like the look of these and all you need to do to run them is drill out the stud holes to 8mm
 
You must log in or register to reply here.
Back
Top