Straight plug engines are better than angle plug engines

nidyanazo · Jun 28, 2011

It's getting almost comical the amount of customers who want the angle plug engines (we do sell both types) simply because they think the angled plug is a better engine with more power.

A centered spark plug will promote a more even burn, with the combustion force able to spread out evenly from the center outwards in all directions VS an angled plug that will heat up the side of the piston of which it's closest to.

Look at all Japanese and European two stroke engines, and see how the spark plug is positioned. Yup, you got it- it's in the center of the head standing straight up and down.

The angle plug design was only adapted to the bicycle engines for more clearance on smaller frames. It is a compromise, not an advancement in engine design as propagated by so many people.

biknut · Jun 28, 2011

On mine the angled plug still ends up in the middle of the combustion chamber.

John the Chimp · Jun 28, 2011

One better then that. What cylinder heads do every drag race team run? You got it! Hemi heads! Where is the plug in those? You guessed it! The very center of the combustion chamber. Thanks for bringing this to my attention. Great post.

kolomootro · Jun 28, 2011

has anyone verified how much stronger an angled plug is compared to a straight one?

bairdco · Jun 28, 2011

i've verified it for myself. all my straight plug engines run circles around the slant heads.

slant heads are prone to warping and blowing head gaskets, also.

nidyanazo · Jun 28, 2011

Edited original post with a photo for reference.
On the left is the center plug head.

dmb · Jun 29, 2011

for the last 25 years hemi heads run 2 plugs for a complete burn [piston schrouding]

biknut · Jun 29, 2011

It's not like this would be the first time a supposed performance modification didn't actually do anything lol.

Goat Herder · Jun 29, 2011

dmb said:
for the last 25 years hemi heads run 2 plugs for a complete burn [piston schrouding]

So we need double slant heads laff

kevinkrg6 · Jun 29, 2011

dam. I just bought a slant head! I hope it holds up for me.

Fulltimer · Jun 29, 2011

I have a slant head but the proof is in the picture. If you look at how the combustion would flow the center upright plugs looks much better. EXCEPT for the finish work! Yuk!! LOL

Terry

James912 · Jul 22, 2011

If you have a slant head and are not satisfied, buy a flat head for your engine. Simple as that.

If it fits...

sportscarpat · Jul 22, 2011

I have both angle and straight plug heads. Straight plugs seem to run smoother with less four stroking. I also think the straight plug head looks better.

mapbike · Jul 22, 2011

Here is how the straight plug head and the slant heads I have look, the one shown in the first post looks to have a squish band and the 2 straight plug heads I have don't have a squish band as can be seen in the pic.

all I know is that I took a straight plug head off one of my engines and put a slant head on it without any other mods and the engine had a very noticable increase in vibration and very little if any difference in power, all I have is an engine that buzzes much more than it did before so it will be getting the straight plug head back as soon as I get the upgraded wrist pin needle bearing installed.

I also have another straight plug head that I plan to put on my other engine that has a slant on it now, it already runs pretty smooth up to 34MPH but I want to see if the other head will smooth it out any like it does on the other engine.

Peace

sportscarpat · Jul 22, 2011

I think the added compression of the slant head leads to more four stroking. Lower compression seems to runs smoother.

mapbike · Jul 22, 2011

sportscarpat said:
I think the added compression of the slant head leads to more four stroking. Lower compression seems to runs smoother.

I'm leaning strongly to agree with you on that point, I thought that i would boost compression and notice fairly good HP & Torque increase but if there was any at all it was very slight and not at all worth the increased vibration it caused, the bike would run in the 30's before and it still ran in the 30's and seemed to pull the hills a about the same with either head, I'm thinking that what is lost in the compression area may be mostly gained back with the straight plug head in the possibly more effecient combustion area of the straight plug heads, I could be wrong on this but my engine just ran so much smoother with the straight plug head and I've always believed that when one of these engines is vibrating real bad it is loosing power from all that imbalance.

Peace

silverbear · Jul 22, 2011

Interesting. Now there will be a run on flat heads.
SB

Goat Herder · Jul 22, 2011

silverbear said:
Interesting. Now there will be a run on flat heads.
SB

Yes this consensus would have to follow suit with the billet heads that are way higher compression as well? rotfl

DuctTapedGoat · Jul 23, 2011

What I would like to see is a hemi 48cc piston. The RAW 66cc has a hemi, and were I to try and boost compression, it would be through that route.

Wm Holden · Jul 23, 2011

maybe two head gaskets on a slant head to lower compression?

Straight plug engines are better than angle plug engines

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