HP Quest per cubic inch
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Cruiser
Joined: Jul 2015
Posts: 143
Likes: 36
From: Florida
HP Quest per cubic inch
I'm not happy with my set up. Currently have A/C, S&S Powertune duals,S&S MR103 cams, FP3, V&H Monster Ovals, on a 15 Road Glide. I have not dyno tuned the bike yet. I will be doing this soon to see what it is making now.
So how to achieve 1.1 Hp per cubic inch with a 103 motor, a 113 hp would be wonderful. In a performance car motor 1.3 to 1.4 hp per cubic inch is a pretty good number to get.
Why is it so hard to do this with a our motors?
I can't justify a big bore kit to a 106 or 107 and gain what?
My thoughts are leaning to the heads, throttle body, tuner, compression ratio and spark delivery.
I was thinking of having the heads done the down time would be a killer.
My other heads to look at are the S&S not sure which ones would be best, 79 cc or the 89 cc. with the same cam.
I'm wondering what CR is the highest to go with pump gas 10.2, 10.5?
I will ditch the FP3 and go with PV.
Upgrade the throttle body with the Harley 58mm unit.
Is the stock ignition adequate or upgrade to what?
I will admit this is my first time trying to hop up a Harley motor, but not my first rodeo. I'm capable to do my own installation, but will need it to be tuned.
I will be visiting with a local shop for the dyno session, he has already told me he will not tune with the FP3, wants to sell me the PV license, I need to confirm with him that he will give me a copy of the file before hand.
So thoughts on this combo would be welcomed.
S&S heads
58 mm throttle body
MR 103 cam
Stock 103 pistons
Power Vision tuner
S&S Power Tune Duals
High flow A/C
Thanks
So how to achieve 1.1 Hp per cubic inch with a 103 motor, a 113 hp would be wonderful. In a performance car motor 1.3 to 1.4 hp per cubic inch is a pretty good number to get.
Why is it so hard to do this with a our motors?
I can't justify a big bore kit to a 106 or 107 and gain what?
My thoughts are leaning to the heads, throttle body, tuner, compression ratio and spark delivery.
I was thinking of having the heads done the down time would be a killer.
My other heads to look at are the S&S not sure which ones would be best, 79 cc or the 89 cc. with the same cam.
I'm wondering what CR is the highest to go with pump gas 10.2, 10.5?
I will ditch the FP3 and go with PV.
Upgrade the throttle body with the Harley 58mm unit.
Is the stock ignition adequate or upgrade to what?
I will admit this is my first time trying to hop up a Harley motor, but not my first rodeo. I'm capable to do my own installation, but will need it to be tuned.
I will be visiting with a local shop for the dyno session, he has already told me he will not tune with the FP3, wants to sell me the PV license, I need to confirm with him that he will give me a copy of the file before hand.
So thoughts on this combo would be welcomed.
S&S heads
58 mm throttle body
MR 103 cam
Stock 103 pistons
Power Vision tuner
S&S Power Tune Duals
High flow A/C
Thanks
Road Warrior
Joined: Aug 2015
Posts: 1,712
Likes: 410
From: Puyallup, WA
Because it's essentially a farm tractor engine.
Seasoned HDF Member
Joined: Dec 2009
Posts: 9,165
Likes: 1,910
From: Doghouse... mostly
Step #1 would be to ditch the Power Tune Duals with the V&H Monster Ovals and get a D&D Fatcat system. That should almost get you where you want to be with no other mods to your plan.
Club Member
Joined: Mar 2016
Posts: 11,688
Likes: 22,266
From: Clearwater, Idaho
Funny, I've been around farms all my life, and I've yet to see a 5500 rpm V-twin farm tractor. I hear this chit all the time, though.
Good starting point.
I had the mr103s. My thoughts are the cams work good as a bolt in. My dyno said 98/112 and I think that is a little high. I even told the dyno operator my thoughts.
I'm now building a 124.
If you we're doing headwork or buying heads and were to raise the compression you should change the cams to best suit those mods. Best thing to do is set your budget, and talk to a shop or one of the forum sponsors.
I'm now building a 124.
If you we're doing headwork or buying heads and were to raise the compression you should change the cams to best suit those mods. Best thing to do is set your budget, and talk to a shop or one of the forum sponsors.
Club Member
Joined: Jun 2007
Posts: 45,429
Likes: 2,898
From: Bedford UK
You're not going to achieve those numbers you want all by yourself! You need expert input, from a suitable tuning shop, to provide a balanced set-up with matched porting, cams, CR, etc, all finished off with a dyno tune. We have HDF sponsors, expert engine people who will probably be delighted to hear from you and sort out your challenge. They post in here often enough.....
Seasoned HDF Member
Joined: Mar 2010
Posts: 21,114
Likes: 7,638
From: Poolville
Seeing that your in Florida you have access to Kirby's V-twin Racing in Deland. He is one of the better builder in the south east....Here's a link. I myself have made increment changes and threw a lot of money away till my final all out build... save your time and money and do it once.....
https://www.yelp.com/biz/vee-twin-racing-deland-4
Call him and go right to a 107" build or 110". you won't be satisfied till you do.....120's hp & tq.....
https://www.yelp.com/biz/vee-twin-racing-deland-4
Call him and go right to a 107" build or 110". you won't be satisfied till you do.....120's hp & tq.....
Last edited by 98hotrodfatboy; Jun 27, 2017 at 06:04 AM.
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Road Warrior
Joined: May 2011
Posts: 1,956
Likes: 439
From: florida
Having done many builds of different sizes I totally agree w hotrod. When you enter the 120's in power it's very satisfying and really is all you need or want on the street. Very reliable and definitely best bang for the buck.
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Road Warrior
Joined: Mar 2013
Posts: 1,923
Likes: 587
From: Alorton, Illinois
IME stock heads won't go any better than 100hp. Stock throttle body is somewhere around 115hp. A 120/120 engine isn't hard or considered max effort.
Compression limits? 11.5 with a cam that closes in the 50 is apples to oranges compared to a 10.5 with a cam that closes at 40. Better to look at corrected compression for limits.
Take your time and do some research. Get a good combo together and 1.1-1.2 is easily reached.
Compression limits? 11.5 with a cam that closes in the 50 is apples to oranges compared to a 10.5 with a cam that closes at 40. Better to look at corrected compression for limits.
Take your time and do some research. Get a good combo together and 1.1-1.2 is easily reached.