M8 128 build horsepower and torque issue
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3rd Gear
Joined: Dec 2021
Posts: 7
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From: mesa AZ
M8 128 build horsepower and torque issue
Hey All, looking for some advice or feedback on my 2019 Road Glide Build. It is at the dealer and the technician is having trouble getting better numbers from the original build that was 130+ HP and 140+ tq. After having the heads completely done by Branch&Okeefe and adding the Fueling 592 cam the numbers stayed the same. The Tech is scratching his head as am I, we expected a much better result. Is it the Throttle body, ECM, cant figure it out? the tech wants to try a larger TB, thinking not enough with all the work dont to the heads and the larger cam........Any suggestions. We thought we would be high 150's-160's hp/tq The build is below.
S&S 128 Kit
Feuling 592 Cam
S&S QUICKEE PUSHROD KIT
Darkhorse Balanced crank w/balancer removal (Cirrilo rods)
B&O inc heads oversized valves
S&S Premium Tappets and Tappet Cuffs
S&S Roller Rocker kit
Darkhorse Compensator
Trask Clutch Basket
Rekluse Torq-Drive Clutch
HPI 62mm Throttle Body
HPI 6.2 injectors
Fueling Narrow Band O2 sensors
PI V2 air cleaner
S&S Oil Pump
Fueling Cam Sproket
AIM Clutch Slave
AIMSDR Clutch
D&D Billet Cat Exhaust Big Bore Baffle
Drag Specialties Performance Coil NGK Iridium Plugs (IX CR9EIX)
Screamin Eagle 10mm plug wires
S&S 128 Kit
Feuling 592 Cam
S&S QUICKEE PUSHROD KIT
Darkhorse Balanced crank w/balancer removal (Cirrilo rods)
B&O inc heads oversized valves
S&S Premium Tappets and Tappet Cuffs
S&S Roller Rocker kit
Darkhorse Compensator
Trask Clutch Basket
Rekluse Torq-Drive Clutch
HPI 62mm Throttle Body
HPI 6.2 injectors
Fueling Narrow Band O2 sensors
PI V2 air cleaner
S&S Oil Pump
Fueling Cam Sproket
AIM Clutch Slave
AIMSDR Clutch
D&D Billet Cat Exhaust Big Bore Baffle
Drag Specialties Performance Coil NGK Iridium Plugs (IX CR9EIX)
Screamin Eagle 10mm plug wires
Seasoned HDF Member
Joined: Jan 2008
Posts: 13,621
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From: State of Confusion
here's where you want to be redirected to..where the professionals / subject matter experts reside
https://www.hdforums.com/forum/ignit...-injection-55/
and The Dyno Room section
https://www.hdforums.com/forum/ignit...-injection-55/
and The Dyno Room section
Club Member
Joined: Dec 2014
Posts: 10,734
Likes: 3,755
From: SWFL
And I thought I read somewhere that M8s dont like iridium plugs? Put stocks back in maybe.
Seasoned HDF Member
Joined: Jul 2013
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From: In my head
If his dealer did the install, its unlikely anything other then bolt on was done. So if so, the S&S standard 128 kit is 11:1 comp. I dont know that cam but those numbers are what Id expect from a mediocre tune. A good dyno shop should get another 10 on each side.
And I thought I read somewhere that M8s dont like iridium plugs? Put stocks back in maybe.
And I thought I read somewhere that M8s dont like iridium plugs? Put stocks back in maybe.
The problem I see here is that you changed two things. Either one or both could be the problem. One thing is, what heads did you send in to have reworked? For the most part, the stock heads flow about as much as you need. The ports on them are bigger than the ports on the SE heads. Just shows that a bigger hole doesn't necessarily mean more or better flow.
I would go back to the cam that you had in it when you first dynoed it, see what you get then. If you do better, then you know the heads are working, making more power. If you do worse, then I would say the heads didn't do anything for you. By the way, you didn't say what cam you were running when you dynoed the first time.
I would go back to the cam that you had in it when you first dynoed it, see what you get then. If you do better, then you know the heads are working, making more power. If you do worse, then I would say the heads didn't do anything for you. By the way, you didn't say what cam you were running when you dynoed the first time.
Club Member
Joined: Dec 2014
Posts: 10,734
Likes: 3,755
From: SWFL
The problem I see here is that you changed two things. Either one or both could be the problem. One thing is, what heads did you send in to have reworked? For the most part, the stock heads flow about as much as you need. The ports on them are bigger than the ports on the SE heads. Just shows that a bigger hole doesn't necessarily mean more or better flow.
I would go back to the cam that you had in it when you first dynoed it, see what you get then. If you do better, then you know the heads are working, making more power. If you do worse, then I would say the heads didn't do anything for you. By the way, you didn't say what cam you were running when you dynoed the first time.
I would go back to the cam that you had in it when you first dynoed it, see what you get then. If you do better, then you know the heads are working, making more power. If you do worse, then I would say the heads didn't do anything for you. By the way, you didn't say what cam you were running when you dynoed the first time.
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Yeah, that's part of it. There's a lot I don't understand about it, but this I know, just because it looks good on the flow bench doesn't mean it will work well on the engine.
