Lots of wiggle room there; must be trade secrets. Has to be some rule of thumb; always is, all the years of data notwithstanding. I am looking at a 98" build; heads will flow in the 280cfm range, cams are Crane 296-2s, early (stepped) Bassani 2:2 Pro Street exhaust. Two throttle bodies on hand, early OEM bored to 46mm and a Kury 57mm which I am told flows about same as HPI 55mm. Everyone says run the Kury 57 but I am not convinced the Kury is a bit overkill and that the 46mm, with more injector, might work fine but that is not based on any data.

 

After building T/C's for almost 16 years now, and seeing the trends that Marrelli/S&S dual runner set-ups/OE early Delphis bored/late Delphis bored/HPI t/bodys/S/E t/bodys/S&S units have shown us, we can pick/choose very accurately using our "in house" cylinder head flow numbers/cam/cubic inch, and the desired power output and intended use.
Scott

 

Its not wiggle room or trade secrets, it's simply there are no absolutes when it comes down to trying to determine how the overall combination is going to be affected when you change one component there of. The only way to know the answer is to test both throttle bodies and rely on data validation rather than theory. With that being said, my gut feeling with your combo is the 46mm unit may be slightly better than the Kury 57 under the curve, however the 57 may make slightly more Hp in the upper RPM's.

 

glad you know the straight dirt on this Jamie- wondering what the logic was with tb/inj change on softail and not dyna, given both had cam upgrades? Not expecting you to know, more of a general "that's odd" question.

 

Thanks Jamie; that is my thinking as well. I would prefer "slightly better under the curve" and hang on to the Kury 57 for a bigger inch motor.

 

Nothing wrong with that at all- That's how most of us do. But, if I go to a tuner and he gives me some advice on something I personally know zero about, I'm not going to answer related questions and make claims in a forum as an expert- especially 3 years later after the fact.

Hinted / probably? You said "fact". so where is that?

Yeh the 4.9 is a mistake on my part- but you missed the point. Is 4.3 larger than 3.9? yes. My credibility is fine. If my credibility with you is not fine, that's more your loss than mine.

Quiz time: FM's post, how many HP max can 3.9's support at stock fuel pressures? Answer: whut?

Cams ARE the later on upgrade for the immediate future. But as anyone with a bike knows, things change regardless of how you feel about it today.

Again, state your facts for comments like 'little merit or sensibility'. Pony up and lets see your credibility. Q: If I'm seeing regular high IDC beyond 80%, then what is YOUR expert recommendation if not larger injectors? What is the flow rate of the stock 103" heads vs the flow rate of a 46mm TB? You gotta know that right? How else could you make such bold general conclusions.

You're the one with the magic 115hp bike that runs ***** to the wall fine on small injectors operating well below max limits- tell us how it was done?

 

Your bike won't be any faster with your tbody upgrade so do what you want with the Costanza upgrade I really don't give a sh*t about what a wad from SoCal does with his wheels. Enjoy your heavy breakout that with pulleys will shift like a dirt bike and still be slow.

 

whoa- so now you're a gearing ratio genius as well? amazing. come on dude, dial it down a notch this is only a forum. folks disagree all the time. I'm always open to counterpoint and correction if the data is sound. If it's not, I raise the BS flag. It's what I do.

So in the spirit of keeping things educational, have a look at one of my run logs from today. if you had something like the powervision to log data with you'd see similar from your own bike. unzip file and open it in excel- at the top of file see the highlighted columns to far right, Y and Z. look at the Injector Power INJ PWR F and INJ PWR R columns. - injectors only have 20ms max to deliver fuel. I'm pushing over 20 in some areas at high load and half throttle. this is also affecting accurate AFR ratios.

If you put your stubbornness aside and take a look at it, you'll understand that larger injectors will benefit this as well as other similar situations- even on a stock improved or mildly cammed motor. no one is talking about making the bike faster here, just running optimally and maintaining performance. Although a top HP build with too small of injectors will be limiting it's HP potential.

 

LA. I have followed this thread with great interest and after having done so I have a few questions.

In your original post you mention exhaust and tuner as the only CURRENT mods with the intent to put cams in later. I could be wrong but that is the way I read it.

If I didn't read it wrong I would question why you are seeing such high duty cycles on an otherwise stock engine.

My question is this. I see you have a PV with TT. There was another perso. I. The forum that installed a TT in his exhaust and placed the O2 sensors real close to the heads and not the stock location provided by exh manufactures. Having said this was it you that detailed the sensor install? If not are your sensors installed in the 18 mm holes provided by the exh manufacture?


I would also double check fuel pressure. Based on what I have read the stock injectors on your 2013 bike should have more than adequate flow for even a stage I motor.

As for future proofing. I have not had an opportunity to look or collect logs on my ride. I have 211 cams, FM billet AC and rinehart 2-1 exhaust. If memory serves me correctly when the tuner got done it was above 90 hp and just above 100 tq. I think 96 hp and 106 torque. So based on 411 from FM a injector upgrade may help me if I want to make more power as I appear to be at or very near the limit of the 3.9 injectors.

Could I squeeze more, probably with a PV and TT. But I am happy with the way she rides and sounds plus I am rarely riding her that hard. She's a 14 heritage classic btw.

As such in real interested in how this all plays out as who knows. Maybe a 107 kit will be in my future once the ESP runs out

 

Hey rbeamj- thanks for your post. Yes currently I only have the VH pipes, SE A/C and PV/TT with richer fuel tuning for E10 gas. I also have the belt pulleys upgraded to 30/70.

I've been seeing high IDC's ever since I started logging data with the PV, even when I was only using the stock narrow band sensors- although it was not as high with the HD provided stage1 map, which is still rather lean. moving to tunes that are more for performance and lower ET's on a mainly town bike have progressively pushed my IDC's higher in the mid to upper MAP and upper rpm areas. From what I have learned this is typical for those size injectors on a 103" motor. Log your data and do some more aggressive riding, harder accelerations through upper rpms.

Bottom line, horsepower requires fuel. injectors are sized according to intended hp of the build and intended use of the build. All opinions aside, the injector math behind 3.9's at HD's rated fuel pressure is at most (realistically) 100hp, and that is 'static' rating. In operation, injectors commonly deliver slightly less fuel than their static rating. You don't want to run injectors beyond 80% of rated delivery consistently otherwise they spray inaccurately and eventually fail. if you ride mellow, run a stock hd tune or even a hd stage 1 tune and never really get on it more than once in a blue moon, well it really doesn't matter much since you rarely if ever are calling on the motor's max hp and fuel delivery. in those cases there is not much consequence of hitting a high IDC on occasion.

So- if your motor is outputting 80hp or more, and you 'get on it' and actually use that 80+ hp, you will be into the max IDC range more often than not. your ride log data will always confirm this. if you have a 100hp max motor, sure, 3.9's can work, but realistically you'd want injectors sized for at least 120-130hp. this way when you use all 100hp, your injectors are always operating below max IDC and more optimally. Or as Jamie said earlier, increase the fuel pressure which will deliver more fuel through the same sized injector.

With your bike and current build, going to larger injectors may or may not give you more HP. But, they will ensure you have complete and more accurate fuel delivery under higher horsepower situations, and give you some added overhead for future upgrades. But like I said, log your ride data- if you see regular high injector times at 16ms or above, you are in max territory. If you never see that, then save your $


On the WB O2 sensors, placing them by the head is the correct location. the 18mm bungs provided on some pipes are designed for narrow band 18mm o2 sensors on earlier HD models- especially pipes with the "dual bung" insert so you can run 12mm or 18mm in the same hole. this allows the pipe to be used on both early and late model FI HD's.

Narrowband O2 has to be father away from the head in slightly cooler exhaust gas, normally about 12" or so from head. Wideband O2 needs to be closer to head in the hotter exhaust gas, normally 3"- 6" from the head. See this guide, page 5, for pic of typical placement of WB O2 bungs- you'll always see the bung about 3" to 4" from the head on most all aftermarket or modified HD pipes designed for WB operation.
http://www.powercommander.com/downlo...8200017.03.pdf

Hope this helps- just remember for EFI-related upgrades don't listen to opinion (mine or anyone else's), look at the injector math, look at your ride log data, and if you think there is a problem that needs solving talk to a couple of the verified expert tuners (FM, HPI, Hillside Cycle, RB Racing, etc). Most all of them will take a couple minutes to lend some guidance.