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4evrshovel
06-12-2017, 12:04 PM
I hear a lot about knocking the baffles out of a fuel injected dyna. People say you can't knock the baffles out of fuel injected engine. I am told that it needs the back pressure. What is everyone's thoughts?

Dougtheinternetannoyance123
06-12-2017, 2:58 PM
Well, lets get the particulars out of the way first. I dont own a Dyna or late model Big Twin, and unless I win one in a raffle its unlikely to ever happen.
(I am still considering an EVO FXR as those are cool) But on V twins I like performance so I have Sportsters, Buells and Ducatis and a bunch of old shit that is not relevant.

But I do know enough to be dangerous and learning more all the time about tuning modern EFI systems. I have the tuning and computer programs for Buells and they are totally plug & play. Same with the 998 Ducati Super bike and aint no restrictions on that bad beast. Its got a full Stainless Termigioni exhaust.

You should research the particulars for YOUR model bike and the computer system. But heres what I know, The systems ALL allow SOME tuning and self learning. The system WILL adjust and compensate to some degree. How much depends on the system. So are very intuitive and even the stock Brain box can be kept and will do just fine. Some require a reflash with modifications to the MAPS that control spark and fuel. Some require a complete replacement of Brain boxs set up to run with a modified bike.

Maybe you are already aware,, But on every HD forum there is the discussion of the HD tax & stage tuning your HD, Stage 1-4 is common and most people do it as they can afford and over time. Step one is Air Cleaner and mufflers and a few other things. Its gets progressively more expensive after that.

Buells are the cutting edge of the HD design, and I own a bunch of Buells and love them. (Tubers and XB). There is a TON of education there for perf and tuning but even a base model Buell is miles ahead of a Sportster. Most base model Buells start out stock near or right at 100hp at the rear wheel, and a base 883 is high 30s to low 40s in HP and a 1200 sporty is high 40s or low 50s in hp.
But the HD tax is shorter and easier on a Buell, Air box, Exhaust and improve cooling, easy. No baffles or super quiet exhausts. SOME is needed and they tune for performance on all types of Buell exhaust.

Many of the Big twins use a tuning box tacked ONTO the factory system and I have not kept up what works and what does not. Theres a lot of garbage out there and pays to research what works.

To answer about back pressure?? YES>> you gotta have some or they run like shit. The only time any motor does well with zero back pressure is on a race engine run at full throttle 100% of the time. But even HD drag bikes have carefully tuned exhausts to maximize performance.
I have spent 4 decades learning this stuff and dont even know half of it. But one of the bikes I worked on holds 2 records currently at Bonneville. So, as I said,, I only know enough to be dangerous.

But read thru these guys website. I love their attitude and no BS approach. They also KNOW their shit. They do a better job explaining much of what you need better than I can.

See: https://www.rbracing-rsr.com/lsr21.htm

farmall
06-13-2017, 3:20 PM
(I am still considering an EVO FXR as those are cool)

Much love on my part for the "Isolastic Evo" (John Favill had a hand in both projects). It's the closest big twin to Sportster agility and quite comfortable. You can stuff any big twin including Twin Cams into the chassis easily. All the other big twins weigh more stock.

As for EFI, I'd copy success (dyno sheets are acceptable evidence) when fucking with EFI. It's not voodoo for mild street tunes. vtwinforum and Harley Tech Talk are good places to research that stuff, particularly vtwinforum since it's a have for old farts with lots of money and you can learn from their mistakes and successes.

The RB Racing page is always worth reading.

Dougtheinternetannoyance123
06-13-2017, 3:41 PM
Much love on my part for the "Isolastic Evo" (John Favill had a hand in both projects). It's the closest big twin to Sportster agility and quite comfortable. You can stuff any big twin including Twin Cams into the chassis easily. All the other big twins weigh more stock.


The RB Racing page is always worth reading.

HA!.... +1 again Farmall. Yep, the RB racing guys are the go-to authority and dont sugar coat a thing. I love sending people there for an
Edu-mah-cation.!!!!!!!!!!!!!

And interesting (And a bit of thread hijack) but great you mention John Favill. Many dont know but the rubber-baby-bumper buggy Norton Comandos were in many parts John Favills engineering along with some other English nutters. Its interesting what they pulled off with a company on a shoestring budget and perpetually underfunded. HD WANTED that design, so when Norton said NO! They hired John instead.

They went at it another way (different patents) and another upstart shit stirrer engineer got his start on that project as well who ended up making a name for himself... Eric Buell. So,, being a Norton-Buell-Sportster guy,, do you see a pattern here?

So, had the good fortune to have a tech talk seminar at the Norton rally last summer with John Favill on some of these topics,, I wanted to get more discussion on the Buell angle as well as comparisons between working for Norton and HD,, He did touch on that a bit, but not as much as I was hoping. But the difference in engineering and budget was night and day.

back to the topic at hand,, I have spent the last couple years reading and learning the Buell EFI systems and to a lessor degree Ducati too. Very adjustable. I can tweak or run any MAPS I want for whatever setup I want. Some of the other systems are not so easy. My expeience with them is basically only knowing how they work,