Merch Fat8
Grand HDF Member
Joined: Sep 2022
Posts: 4,255
Likes: 3,675
From: Florida
You're missing the point here, it's meant to increase performance on the Evo platform, not install a M8 drivetrain.
That Ultima you have is pretty much a TC top end on a larger bore beefed up Evo case, why did they build that?, because the heads are better and more displacement.
Why do the same thing with the M8 heads?, because the heads are better, bone stock will easily support 140hp and you get dual plugs and ACR's to boot, mosey over to Ebay and pick up a set for about $300.
I'm sure the cooling could be utilized,,,, if needed, lets wait and see.
That Ultima you have is pretty much a TC top end on a larger bore beefed up Evo case, why did they build that?, because the heads are better and more displacement.
Why do the same thing with the M8 heads?, because the heads are better, bone stock will easily support 140hp and you get dual plugs and ACR's to boot, mosey over to Ebay and pick up a set for about $300.
I'm sure the cooling could be utilized,,,, if needed, lets wait and see.
If a measure of reliability is needed and it’s a street/strip application I haven’t personally seen the 4 valves created on average more than the 1.2 per cube number we already have from EVO & TC. Sure I’ve seen them make more than 1.2 but reliability went out the door same as an EVO.
The big advantage I see with M8 is it isn’t an after market solution… it’s Harleys base that’s making the 1.2 per cube at the 114-135 inch motors.. so that’s impressive. With this scenario, that advantage isn’t still there… you’re building largely from aftermarket already.
I’d like to try an M8 one day. But I want to try it because I think the water and oil cooling is the right direction and will lead to greater longevity with that 1.2 per cube average. My hold up is money… and wanting to wait until the magneto or other ignitions are more fleshed out and developed.
Last edited by Rains2much; Apr 25, 2026 at 11:21 AM.
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,830
Likes: 7,968
From: poway
If it’s not taking advantage of the oil or water cooling… no advantage there.
Add an external oil pump and cooler to feed the heads?
Seasoned HDF Member
Joined: Mar 2010
Posts: 21,025
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From: Poolville
Im in no way saying that this wont prove to be an awesome upgrade.. Or that it wont make sense to do. Im merely trying to understand and see quantifiable proof. My questions are not meant to sound challenging or skeptical, they really are me trying to know. I guess I need to see on 124-140 cubes that the M8 Heads make more power than aftermarket EVO heads. If they do
then I get that. But I dont know that they do? Im not saying that they dont, only that I havent seen that as a known average.
If a measure of reliability is needed and its a street/strip application I havent personally seen the 4 valves created on average more than the 1.2 peer cube number we already have from EVO & TC.
The big advantage I see with M8 is it isnt an after market solution its Harleys base thats making the 1.2 per cube at the 114-135 inch motors.. so thats impressive. With this scenario, that advantage isnt still there youre building largely from aftermarket already.
If a measure of reliability is needed and its a street/strip application I havent personally seen the 4 valves created on average more than the 1.2 peer cube number we already have from EVO & TC.
The big advantage I see with M8 is it isnt an after market solution its Harleys base thats making the 1.2 per cube at the 114-135 inch motors.. so thats impressive. With this scenario, that advantage isnt still there youre building largely from aftermarket already.
you need to listen to Bryan/Schex, he knows what he's talking about...
Seasoned HDF Member
Joined: Mar 2010
Posts: 21,025
Likes: 7,549
From: Poolville
One thing that I question is.. What are they going to do with the cooling passages in the heads?? All M8 heads have them.. In the info provided, they mention a bigger oil pump and piston oilers but I doubt any pump that fits in the stock evo location will have enough volume to feed the heads passages.
Add an external oil pump and cooler to feed the heads?
Add an external oil pump and cooler to feed the heads?
Grand HDF Member
Joined: Sep 2022
Posts: 4,255
Likes: 3,675
From: Florida
Just want you to know that these M8 heads are now producing 1.3-1.4 hp/cube without stressing the **** out of the bottom end.. No your not building from aftermarket.. The power window is almost endless....
you need to listen to Bryan/Schex, he knows what he's talking about...
you need to listen to Bryan/Schex, he knows what he's talking about...
I don’t remember the user name but I did see one here on this sight that was like 170 outta I think a 131 and if memory serves he was coming up on 10k miles.
Last edited by Rains2much; Apr 25, 2026 at 02:01 PM.
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,830
Likes: 7,968
From: poway
The HVHP pump does not have gerotors but has gears and runs 1/2 the speed of the crank where an M8 oil pump runs on the crank, same speed.
The M8 oil cooled feed pump is roughly 75% wider than the coolant version pump.
Grand HDF Member
Joined: Mar 2018
Posts: 3,851
Likes: 3,401
From: Arizona
I have no intention of buying a new Harley. I want to keep my Evo machines on the road. I'm curious as to the costs and the use of OEM hardware.
I like the idea of updating older bikes with newer parts without riding the down payment of a house. Motorcycles shouldn't be massive investments.
I like the idea of updating older bikes with newer parts without riding the down payment of a house. Motorcycles shouldn't be massive investments.
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From: SE Louisiana
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From: SE Louisiana
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,830
Likes: 7,968
From: poway
M8 uses a tap off of the feed side pump to the cooler and from the cooler to the heads. The head oil returns to the oil tank separate from the oil fed into the motor. It's in the service manual..
You don't want to use the return for oil cooling.. Oil is aerated. Cooling efficiency is poor.
Last edited by Max Headflow; Apr 26, 2026 at 08:32 AM.