S&S Intake Manifold
#1
06-23-2019, 07:44 AM
S&S Intake Manifold
I learned something’s about air flow & a Harley, this weekend & thought I would share.
Earlier this year, I put the Lowrider in the shop for some modifications & one was to install a new Mikuni HSR 42.
Dynoed about 86 hp & 88 ft.lbs. torque. Not shabby for a stock bore & stroke evo.
When I got her back I didn’t like the fact that the backing plate that Mikuni provides with the carb kit, is plastic.
So, without consulting my Indy, I put my old solid aluminum cv backing plate back on, with adapters for the new carb.
While I was changing out things , I figured I’d go ahead & put my old S&S intake manifold back on , in place of the Mikuni manifold.
Now , keep in mind the S&S intake ID is .100 bigger than the Mikuni.
Fast forward to yesterday.
I took bike back to Indy, yesterday, to do one dyno pull to make sure all is well.
Found out, by putting that bigger S&S intake manifold on, I lost 5 ft. lbs of torque .
So now, I’ve got to change back to the Mikuni manifold to get her back to where I was.
It made it run richer & loose power by running a mismatched intake manifold.
The Mikuni manifold & the S&S Performance Heads I use have the same size ports.
1 5/8. Stock Harley head intake ports are 1 5/8 , also.
Live & learn.
Ride Safe,
Harold
#2
06-23-2019, 08:23 AM
Seasoned HDF Member
Did the two manifolds look the same inside? When I put my S&S on my bike, complete kit with manifold, it replaced a Screaming Eagle carb set with the SE manifold. The S&S manifold had casting marks and was rather rough, where the SE manifold was very clean and polished. I cleaned up the S&S before putting it on.
Also, your different intake manifold flows different and the carb was jetted for the previous one. If the carb was re-jetted, would it make the same power? Probably easier to just swap the manifold back out.
Also, your different intake manifold flows different and the carb was jetted for the previous one. If the carb was re-jetted, would it make the same power? Probably easier to just swap the manifold back out.
#3
06-23-2019, 08:37 AM
Grand HDF Member
First of all, nice bike.
Second, Thunderheader is the best sounding 2-1 going for years but it's history is also known to be not as strong as others with numbers, did the dyno operator mention anything about the pipe to maybe debunk the myth?
On the manifold you always think bigger is better, I understand the port match at the heads was slightly necked down but also did enough research over the years that port velocity is a factor in creating torque, quicker moving air provided by a smaller intake is good especially on smaller cubes. Your post just provided by equipment the theory of how velocity works.
Bigger cubes create a chit load of velocity when filling a cylinder and a by product is poor street manors because of the quick air being pulled thru a carb, EFI is better but still touchy trying to match the big hit of air being pulled. Old Salty Dog John Sachs explained it to me by opening up the throat on a carb slows down velocity promoting street manors and Zippers Thunderjet tuning instructions also mentions boring the throat. The mod of boring the throat to slow down air also shows the effect velocity on a Harley engine, Harold's information is golden and only picked up by equipment, thanks for posting Harold.
Second, Thunderheader is the best sounding 2-1 going for years but it's history is also known to be not as strong as others with numbers, did the dyno operator mention anything about the pipe to maybe debunk the myth?
On the manifold you always think bigger is better, I understand the port match at the heads was slightly necked down but also did enough research over the years that port velocity is a factor in creating torque, quicker moving air provided by a smaller intake is good especially on smaller cubes. Your post just provided by equipment the theory of how velocity works.
Bigger cubes create a chit load of velocity when filling a cylinder and a by product is poor street manors because of the quick air being pulled thru a carb, EFI is better but still touchy trying to match the big hit of air being pulled. Old Salty Dog John Sachs explained it to me by opening up the throat on a carb slows down velocity promoting street manors and Zippers Thunderjet tuning instructions also mentions boring the throat. The mod of boring the throat to slow down air also shows the effect velocity on a Harley engine, Harold's information is golden and only picked up by equipment, thanks for posting Harold.
#4
06-23-2019, 09:21 AM
Did the two manifolds look the same inside? When I put my S&S on my bike, complete kit with manifold, it replaced a Screaming Eagle carb set with the SE manifold. The S&S manifold had casting marks and was rather rough, where the SE manifold was very clean and polished. I cleaned up the S&S before putting it on.
Also, your different intake manifold flows different and the carb was jetted for the previous one. If the carb was re-jetted, would it make the same power? Probably easier to just swap the manifold back out.
Also, your different intake manifold flows different and the carb was jetted for the previous one. If the carb was re-jetted, would it make the same power? Probably easier to just swap the manifold back out.
Indy said he could re-jet carb with larger manifold, but prolly wouldn't get back the same results, so Mikuni manifold is going back on.
I'll post up dyno result's when I get parts swapped back.
The stock Harley intake manifold & Mikuni manifold are the same size, 1.625.
The S&S I have is about 1.79 ish. Been a while since I measured it. I knew this going in. but thought nothing of it until my indy showed me on the dyno screen the numbers.
No changes were done to the jetting between the dyno runs. The larger S&S intake manifold slowed down velocity as Bagger stated & made it run richer , robbing the engine of torque.
#5
06-23-2019, 09:40 AM
First of all, nice bike.
Second, Thunderheader is the best sounding 2-1 going for years but it's history is also known to be not as strong as others with numbers, did the dyno operator mention anything about the pipe to maybe debunk the myth?
On the manifold you always think bigger is better, I understand the port match at the heads was slightly necked down but also did enough research over the years that port velocity is a factor in creating torque, quicker moving air provided by a smaller intake is good especially on smaller cubes. Your post just provided by equipment the theory of how velocity works.
Bigger cubes create a chit load of velocity when filling a cylinder and a by product is poor street manors because of the quick air being pulled thru a carb, EFI is better but still touchy trying to match the big hit of air being pulled. Old Salty Dog John Sachs explained it to me by opening up the throat on a carb slows down velocity promoting street manors and Zippers Thunderjet tuning instructions also mentions boring the throat. The mod of boring the throat to slow down air also shows the effect velocity on a Harley engine, Harold's information is golden and only picked up by equipment, thanks for posting Harold.
Second, Thunderheader is the best sounding 2-1 going for years but it's history is also known to be not as strong as others with numbers, did the dyno operator mention anything about the pipe to maybe debunk the myth?
On the manifold you always think bigger is better, I understand the port match at the heads was slightly necked down but also did enough research over the years that port velocity is a factor in creating torque, quicker moving air provided by a smaller intake is good especially on smaller cubes. Your post just provided by equipment the theory of how velocity works.
Bigger cubes create a chit load of velocity when filling a cylinder and a by product is poor street manors because of the quick air being pulled thru a carb, EFI is better but still touchy trying to match the big hit of air being pulled. Old Salty Dog John Sachs explained it to me by opening up the throat on a carb slows down velocity promoting street manors and Zippers Thunderjet tuning instructions also mentions boring the throat. The mod of boring the throat to slow down air also shows the effect velocity on a Harley engine, Harold's information is golden and only picked up by equipment, thanks for posting Harold.
From what I've learned thru all this with exhaust systems is the Vance & Hines baffled straight Shots vs the Thunderheader is, the dual exhaust system makes about the same power as a 2 into 1 BUT the dual systems I've seen always have a dip in the torque curve, regardless of what carb I've used . The 2 into 1 , has a smooth , progressive torque curve and makes comparable power..
I've used a S&S Super E, Bob Woods modified CV, & now a Mikuni HSR 42.
I'll update this thread with dyno results when I'm done.
Ride Safe,
Harold
#6
06-23-2019, 12:47 PM
Seasoned HDF Member
As mentioned, Without a doubt port matching is very critical to velocity and higher velocity will increase cylinder fill which will produce more torque. This goes without saying to even include the exhaust system. The loaner motor I have (stoker 89"er) has a Mik 42 and I must say it runs very well...
#7
06-23-2019, 01:08 PM
As mentioned, Without a doubt port matching is very critical to velocity and higher velocity will increase cylinder fill which will produce more torque. This goes without saying to even include the exhaust system. The loaner motor I have (stoker 89"er) has a Mik 42 and I must say it runs very well...
I believe I’m finished experimenting with carbs.
Ride Safe,
Harold
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#8
06-23-2019, 01:17 PM
Grand HDF Member
The 89" had a Mikuni 45 attached it's last 3 years before pulling the engine, wasn't nothing negative can say about it. Good manors, good response, pulled hard and the only thing goofy was the air screw changes went deeper affecting the low jet unlike a CV but figured that one out.
#9
06-23-2019, 01:32 PM
Seasoned HDF Member
#10
06-24-2019, 07:26 AM
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