How Good Are Stock M8 Heads?

[WhipLash96]

I don't have an M8 yet but I have decided that it is time to get one. I know what bike I want and as most of us here think, Stock Bikes Suck!!!

I have been doing some searching and I think that I have found the cam that I want to use, or at least start the blue print with for what my goals are.

In conversation with a close friend, he had stated that the M8 heads are really good and only need minor port work and perhaps only a 2mm increase on intake valve size..... He knows what displacement will be and what cam I am going to use..

Overall, what do you think of the stock heads on the M8 non SE or CVO?

[Don D]

Fine if you want a torquey 135hp. That is the horsepower side, as far as reliability the springs suck plus factory tolerances on protrusion variance is one thing I don't like. One valve 0 lash the other ?? The early SE CNC heads went the wrong way, smaller. The later heads are better but still others have CNC programs for the stock heads, including myself, that work better than the SE Extreme CNC versions. I currently have CNC +1 heads in stock on sale at $1200 exchange, oil cooled black.

[WhipLash96]

Fine if you want a torquey 135hp. That is the horsepower side, as far as reliability the springs suck plus factory tolerances on protrusion variance is one thing I don't like. One valve 0 lash the other ?? The early SE CNC heads went the wrong way, smaller. The later heads are better but still others have CNC programs for the stock heads, including myself, that work better than the SE Extreme CNC versions. I currently have CNC +1 heads in stock on sale at $1200 exchange, oil cooled black.

Good to know. What do the later version of the M8 stock heads flow from stock? High lift.....

[Wookie3011]

Fine if you want a torquey 135hp. That is the horsepower side, as far as reliability the springs suck plus factory tolerances on protrusion variance is one thing I don't like. One valve 0 lash the other ?? The earlySE CNC heads went the wrong way, smaller. The later heads are better but still others have CNC programs for the stock heads, including myself, that work better than the SE Extreme CNC versions. I currently have CNC +1 heads in stock on sale at $1200 exchange, oil cooled black.

What do the stock heads flow Don? 4 valves should be leaps and bounds over twin cam heads but thats just an assumption. I have noticed that the M8's repond VERY WELL to cams. The amount of HP you can get with a cam swap in M8 would cost 4k to get with Twin Cam. That's what I've seen and is the reason I'm also fascinated with M8's. Good price for ready to go heads. CNC+

[Don D]

The big bores are easy too. A guy can bolt on a top end job over the weekend and get it tuned next week all at a decent price tag. There are a lot of essential add-ons however. S&S does a pretty good job with those. Rocker shafts, studs, lifter cuffs, head bolts. I still stock ductile sleeved cylinders and KB pistons for the guys that are wanting higher tier quality. Of course cost is higher too. The ductile sleeves take a pounding plus I am very fussy with my bore and hone jobs.
All the stock heads are about the same but vary due to core shift some. I was referring to early and late CNC Harley Screaming Eagle heads. Stockers will knock down about 320+ intake. It is the exhaust side that suffers. More of a design issue than porting, but porting and larger valves can and does help on the exhaust side.

[hrdtail78]

How good are the heads?  You can do a 124 drop on a 107.  Injectors, minus .500 lift cam, a manifold and a good intake and pipe and you can achieve 140/140 plus with out touching the heads.  While the latest greatest late model TC head would limit you around 100.

[HogMike]

How good are the heads?  You can do a 124 drop on a 107.  Injectors, minus .500 lift cam, a manifold and a good intake and pipe and you can achieve 140/140 plus with out touching the heads.  While the latest greatest late model TC head would limit you around 100.

👍

[ziggy24]

Fine if you want a torquey 135hp. That is the horsepower side, as far as reliability the springs suck plus factory tolerances on protrusion variance is one thing I don't like. One valve 0 lash the other ?? The early SE CNC heads went the wrong way, smaller. The later heads are better but still others have CNC programs for the stock heads, including myself, that work better than the SE Extreme CNC versions. I currently have CNC +1 heads in stock on sale at $1200 exchange, oil cooled black.

Good to know. What do the later version of the M8 stock heads flow from stock? High lift.....

These are from FM/Ward for reference.

Stock M8 Heads

SE CNC Heads

SE Extreme Heads

[WhipLash96]

Fine if you want a torquey 135hp. That is the horsepower side, as far as reliability the springs suck plus factory tolerances on protrusion variance is one thing I don't like. One valve 0 lash the other ?? The early SE CNC heads went the wrong way, smaller. The later heads are better but still others have CNC programs for the stock heads, including myself, that work better than the SE Extreme CNC versions. I currently have CNC +1 heads in stock on sale at $1200 exchange, oil cooled black.

Good to know. What do the later version of the M8 stock heads flow from stock? High lift.....

These are from FM/Ward for reference.

Stock M8 Heads

SE CNC Heads

SE Extreme HeadsYou for posting!

Thank

[WhipLash96]

Fine if you want a torquey 135hp. That is the horsepower side, as far as reliability the springs suck plus factory tolerances on protrusion variance is one thing I don't like. One valve 0 lash the other ?? The early SE CNC heads went the wrong way, smaller. The later heads are better but still others have CNC programs for the stock heads, including myself, that work better than the SE Extreme CNC versions. I currently have CNC +1 heads in stock on sale at $1200 exchange, oil cooled black.

At what lift do the M8 heads need geometry correction or is it needed at all? Also do the M8 heads share the same rocker ratio as the Twin Cam?

[Don D]

The bigger question is why go as high lift as geometry correction is needed? It takes springs that go there that have a combined pressure of 170# seat and 560# open at .625. Lifters are now on the watch list assuming the rest of the top is trussed up to hold that pressure. S&S has done a good job with shafts and the studs and nuts. Their rockers become needed after .550 lift. They are 1.64:1 stock are 1.625:1 ratio. Also pushrods need to have a "mae west" type top to avoid dislodging from the rocker at higher lifts. I would change springs on any performance application running >.500 lift.

[WhipLash96]

The bigger question is why go as high lift as geometry correction is needed? It takes springs that go there that have a combined pressure of 170# seat and 560# open at .625. Lifters are now on the watch list assuming the rest of the top is trussed up to hold that pressure. S&S has done a good job with shafts and the studs and nuts. Their rockers become needed after .550 lift. They are 1.64:1 stock are 1.625:1 ratio. Also pushrods need to have a "mae west" type top to avoid dislodging from the rocker at higher lifts. I would change springs on any performance application running >.500 lift.

I guess the simple answer to your question is "Why Not?" I am trying to learn more about these engines as far as what I can get away with in a semi economical way, (if there is such a thing)? I have a vision for what I want to do and am seeing if it is feasible or not. So far, from what you are saying about the heads, I will have some decisions to make there. Yes, I have have heard that S&S is the place to go for the valvetrain. I am a big supporter of S&S stuff anyways so that is where I would have gone regardless, except for the cam in this application.  

[Don D]

S&S Head bolts and cuffs and you are ready to dive in. Me personally, I have found some grinds that work very well plus tune easy while not becoming real pipe sensitive at < .500 lift.

[WhipLash96]

Right.... I have my goals for the project and cam (as of now), picked. It will be a long and slow process.

So, are the opinions the same for the water cooled heads?

[Oclaf]

so why the secrecy of the cam?

[WhipLash96]

so why the secrecy of the cam?

Not really a secret, it's just possible that my mind will change 40 different times by that time. And, I'm just not going to get into the debate of cams of which one is better and so on. Also, this thread is concerning the heads for the M8 engine and what they are or aren't capable of..

[Don D]

The cam choice is critical with stock heads as the inhibited exhaust port needs crutching.

[Oclaf]

so why the secrecy of the cam?

Not really a secret, it's just possible that my mind will change 40 different times by that time. And, I'm just not going to get into the debate of cams of which one is better and so on. Also, this thread is concerning the heads for the M8 engine and what they are or aren't capable of..

not looking to recommend a cam, nor desire anyone to chime in either, but i believe the heads are dependent on the cam for getting max performance and vice versa...its not as simple as saying they work to xxx...on an EVO i had many moons ago, as i have a 2020 RGS now with M8, but the EVO had Baisley heads matched to the cam as the parts/specs were sent and for an EVO, we are talking 98 bike, late 90's, it had one HP per cubic inch which would be a lot and somewhere around 93 ft lbs of torque...Dyna WG, that thing would scoot and was reliable, did quite a few long rides. But to the point, you will go crazy thinking of myriad of choices, options, etc but no biggie, you do you. i would at least pick something to run with and see where it takes me. Not totally blind but take basic specs and reported outcomes then go with that and marry up with head work, probably exceed expectations. Of both parts manufacturers and oneself.

[WhipLash96]

so why the secrecy of the cam?

Not really a secret, it's just possible that my mind will change 40 different times by that time. And, I'm just not going to get into the debate of cams of which one is better and so on. Also, this thread is concerning the heads for the M8 engine and what they are or aren't capable of..

not looking to recommend a cam, nor desire anyone to chime in either, but i believe the heads are dependent on the cam for getting max performance and vice versa...its not as simple as saying they work to xxx...on an EVO i had many moons ago, as i have a 2020 RGS now with M8, but the EVO had Baisley heads matched to the cam as the parts/specs were sent and for an EVO, we are talking 98 bike, late 90's, it had one HP per cubic inch which would be a lot and somewhere around 93 ft lbs of torque...Dyna WG, that thing would scoot and was reliable, did quite a few long rides. But to the point, you will go crazy thinking of myriad of choices, options, etc but no biggie, you do you. i would at least pick something to run with and see where it takes me. Not totally blind but take basic specs and reported outcomes then go with that and marry up with head work, probably exceed expectations. Of both parts manufacturers and oneself.

I agree with everything you said.  The responses so far has me going away from the stock heads entirely and going with some SE's. I will need flow, and lots of it.

[Don D]

The first gen won't get you anything more than stock. The second gen Extreme heads are 94cc and being that there is limited milling on the M8 heads it does challenge getting the compression up. Some of the pistons offered are stupid with overly large valve reliefs forcing lager than needed domes.

[turboprop]

Good move on not mentioning the cam and keeping the conversation focused on your question about what the heads are capable of.

Most of the talk here is just noise. Me, I would look in the dyno section, particularly at the sheets posted by Sheffler Performance. The owner of that shop has been putting up some really good sheets using untouched M8 heads on big blocks. Those should give you an idea of what untouched M8 heads are capable of.

[WhipLash96]

Good move on not mentioning the cam and keeping the conversation focused on your question about what the heads are capable of.

Most of the talk here is just noise. Me, I would look in the dyno section, particularly at the sheets posted by Sheffler Performance. The owner of that shop has been putting up some really good sheets using untouched M8 heads on big blocks. Those should give you an idea of what untouched M8 heads are capable of.

I agree about your point of "noise." Believe it or not, I in part make my decision on who does the "heavy" lifting of a project based on their ability, or lack there of, to answer a question as it was asked. Especially if the question was posed on a forum.

I have looked at the dyno section some and there isn't really anything there that is making my jaw drop in absolute awe... There are some nice builds there but nothing that I "Have To Copy."

[WhipLash96]

The first gen won't get you anything more than stock. The second gen Extreme heads are 94cc and being that there is limited milling on the M8 heads it does challenge getting the compression up. Some of the pistons offered are stupid with overly large valve reliefs forcing lager than needed domes.

How well do these heads respond to decking? I understand that other things come into play with decking the heads but is there "usually" enough room to remove some material to bring that number down if needed?

[Don D]

You can only take about .040 off of them.

Eyes go to the intake flow numbers but stockers only flow 180 on the exhaust side, on a side note. Camshaft requirements, in my opinion, are different for these VS fully ported heads. Too many play the "good cam" bad cam" game when the cam needs to be picked based on the characteristics of the head port geometry and flow potential, among other things.

[WhipLash96]

You can only take about .040 off of them.

Eyes go to the intake flow numbers but stockers only flow 180 on the exhaust side,

Only 180? At what lift? According to the information that was posted earleir in the thread, the exhaust flow is better than 180..
https://university.fuelmotousa.com/wp-content/uploads/Stock_M8_head.jpg