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Discussion Starter · #1 ·
Hey dudes, I ran across this aftermarket 'Pegasus' fuel injection system. It has some interesting features I think:

1) 53mm throttle body

2) Computer software to adjust 3D fuel map over any point

3) Sensors only measures engine rpm and throttle position

4) Enrichening circuit for cold starting

5) Controls ignition timing and advance curve (adjustable)

This unit is developed specifically for HD's (what else?) and they say it can deliver 150 HP with certain engines. Pretty impressive with an engine turning under 6000 rpm typically.

Here's the problem... for a single throttle body kit it's about $1500 USD. Not bad, but to use a single body you would need to build a custom intake 'Y' manifold and mount the unit sideways, or underneath the intakes and make it an 'updraft' style. No float bowls, so mounting position is flexible.

It would be cost-prohibitive to mount 2 of these systems on your Triumph twin, and besides...53mm is waaaay too big for a dual TB setup! It is probably OK for a single injector setup though...the throat area of a single 53mm bore is 2206mm2. The area of 2ea 36mm (stock) carbs is 2035mm2. Not a huge increase, but the single is roughly equal to a pair of 38mm carbs.

So, the real advantage would be in near perfect fuel delivery to keep the A/F ratios near ideal at all rpms and throttle openings, while delivering instant throttle response, better HP and torque, lower emissions, better economy and...hmmm, did I forget anything? Oh yeah, you don't have to synchronize the 'carbs' anymore.

Since the system is specifically for HD's I think it would take a LOT of tinkering to make it work on the TT's, unless Pegasus would be willing to work with making it fire with 360 deg and 270 deg versions of our twins. The manifold could be worked out I believe, by branch sizing to maintain velocities that deliver the fuel/air to the cylinders evenly, and with very little loss.

Any thoughts? Someday...someone will make a 'universal' throttle body injection kit for older singles, twins, triples, and fours that we all have and love to play around with. It will never be 'cheap', but hopefully the advantages will make it worthwhile.

Cheers!
BLIGHT:motorbike:
 

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I have an 07 Scram,never thought about aftermarket fi. If they ever make something like that for the triumph twins I'd have to take a look at that. I like my bike with its carbs and all(classic) but that is a very tempting option for sure!
 

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The cool thing about that is how integrated it is. The brain is right on top of the throttle body. The injectors are right below. The TPS is built into the side. I read through the install instructions, and it seems like a slick solution for a Harley twin, and incredibly easy to install for a complete fuel injection and ignition system.

Not so much for a Triumph twin, though. It could be made to work, sure, but so could an '80s Chevy TBI unit if you knew what you were doing, and I'm not sure the Pegasus unit would perform that much better.

There's one big problem with the Pegasus kit: It's a single throttle body injection (TBI) unit, and you need to feed two cylinders. Constructing a Y-manifold that performs well is not trivial. It is on a Harley, because the heads were designed to make that possible, but on a Triumph, you'd be looking at unequal-length runners that are each much longer than the original intake tract. Having the injectors at the far end of long runners means potential problems with fuel droplets falling out of suspension and pooling, which kills idle behavior and makes the engine choke under low load. The long runners also work against the claimed "instant throttle response" by adding distance between the throttle butterfly and the combustion chamber. Finally, unless you were careful to tune the resonance of each leg of the manifold, each cylinder would hit its powerband at a different point, which would be a bear to tune.

Also, it's not at all like running a pair of 38s. The cylinders breathe 180 degrees (meaning 360 degrees of crank rotation) out of phase, so that massive opening is available to each cylinder independently at low RPMs, with more overlap at high RPMs. The slower the engine spins, the more it seems like a 53mm opening. The faster the engine spins, the more it seems like a 38. That's exactly the opposite of the behavior you want. Harleys put up with this because they don't spin too fast, and they're generally saddled with a single carb anyway. Making it worse, the intake pulse from the cylinder with the shorter runner would be stronger than the pulse from the cylinder with the longer runner, meaning that the closer cylinder would get more mixture, and thus run even stronger at high RPMs. To even this out, you'd need a substantial plenum behind the throttle body, but, in addition to having to find a place to put it, this would make fuel pooling even more of a problem and weaken throttle response further. Cars do fine with setups like this (look at the setup on the old EFI Mustang 5.0s: big plenum, long runners, single, reasonably-sized throttle body at the front of it, all of which are easy to see when you look at the engine), but they also have their injectors right next to the cylinders they feed. If the injectors were at the throttle body, that system wouldn't work well at all.

On a Harley, none of this matters, because it's easy to design a short, symetrical Y-manifold, so all of these problems go away- with injectors placed on opposite sides of the throttle body, you could even effectively dedicate one injector to each cylinder- and the engines spin slowly enough and make power down low enough that none of this matters. Not so on our Triumphs, though.

Point being, my guess is that FCR 39s would deliver better performance and response, and be much, much cheaper. Mikuni 42s would be even better, and would still be much cheaper (remember, on top of buying the Pegasus kit, you also have to get your hands on that super-complicated manifold, which would need to be custom made).

The hot setup on a Triumph twin (according to me) would be a MegaSquirt 'n' Spark ECU running two throttle bodies with integrated injector bungs. The injectors would be as close to the chamber as possible and the throttle blades would be right behind them. You want throttle response? That's it. You'd also have precise control over how much fuel each cylinder got independently, and if you wanted to tune the intake, you could tune it by adding runners ahead of the throttle bodies. The trade-off is that you'd have to source the parts yourself and balance flow through the throttle bodies. As much of a PITA as that may sound like, it's nowhere near as difficult as getting your hands on that intake manifold would be. On the up-side, if you were creative in sourcing your parts and assembled the MS'n'S yourself, you'd probably end up spending half of what you would on the entire setup to adapt the Pegasus throttle body, and you might even manage to do it for half of what you'd pay for the Pegasus kit alone.

So yeah, those are my thoughts. It's a cool idea, but I think there's an even cooler way to do it that costs less money. For the reasons I've mentioned, I don't think anyone will ever introduce and all-in-one, universal ECU that works across different numbers and placements of cylinders, but we already have all of the universal parts required to assemble your own system (relatively) cheaply for anything you could ever want to put it on.

Just my .02.
 

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Discussion Starter · #5 ·
...The hot setup on a Triumph twin (according to me) would be a MegaSquirt 'n' Spark ECU running two throttle bodies with integrated injector bungs. The injectors would be as close to the chamber as possible and the throttle blades would be right behind them.
Good thinking and analysis there. I pretty much came to the same conclusion...I found the Megasquirt and Microsquirt info last night and was reading a bit how various folks have cobbled together various configurations of 'over the counter' throttle bodies with injectors to put on their bikes.

Ebay is a good source for 'big' used throttle bodies with injectors...acceptable donors: Ducatis, Aprilias, Suzuki TL's, BMW twins, RC51 Honda, etc.

Sensor and electronic installation would not seem overly difficult with the Squirt packages. Mechanical Issues? Linkages to synchronize the throttle blades, setting the injector bodies at the proper spacing for the intake manifolds, manifold adapters, air filter adapters...it would be a long list, and I agree...it probably would not perform any better (and possibly worse!) than a conventional FCR carb conversion.

It does seem like a fairly cheap thing to do though...the Microsquirt is only about $400. Throttle body pairs go for as little as 50 bucks if you're lucky. The sensors for air and engine temps are pretty cheap...still, the verdict?

I'm just not willing to fiddle that much with my perfectly running (if a bit underpowered) Thruxton. It would be out of service for several days I would think before it either worked or it didn't. If it didn't work well, I'd be out $500-600 or more on the experiment and a whole lot of labor and down time just to return it to the state it was.

I guess I just need to be satisfied with the moderate amount of power on tap and enjoy the fun 'retro' ride! However...I keep thinking about the 5-10hp available with a D&D Racing 2into1 headers. I still don't like the looks much, but that's a lot of power to leave hiding in the engine. Apparently the 813 cams are good for another 3-5 hp on top, and finally, get that ignition box recurved with a 8500 rpm limit.

I bet the bike would run noticeably better even without the bigger carbs or injection. Pretty easy way to pick up mebbe 10 hp without taking the whole upper engine apart for a pricey 904 kit.

I recently saw an electric blower that will pressurize an airbox for more power supposedly, but it's for cars and it's pretty big. I believe it only works with fuel injected engines though, since pressurizing a carburetor venturi (and not the float bowl) will cause less fuel to go up the main jet due to reduced venturi vacuum at full throttle.

It's a great forum we have here...lots of creative minds, and folks that are willing to try almost anything (and spend countless dollars) to make the beloved Triumph 790 & 900 twins run maybe as fast as a stock (yawn) Suzuki SV650. Let's all keep up the good work...these retrobikes are worth hot-rodding!!

Cheers!
BLIGHT
 

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It's a great forum we have here...lots of creative minds, and folks that are willing to try almost anything (and spend countless dollars) to make the beloved Triumph 790 & 900 twins run maybe as fast as a stock (yawn) Suzuki SV650. Let's all keep up the good work...these retrobikes are worth hot-rodding!!

Cheers!
BLIGHT
yeah...about that....

I have a buddy, he rides a bone-stock (down to the silencer) sv650. I think it's a 2007. It's EFI. It is boooo-ring to ride. No vibes at all, no feedback, very little power until 6,000 rpms then it's a race to redline. It does come alive on top but it's dead on bottom. A few plusses over the bonnie are that it is dead smooth cruising at hwy speeds in 6th gear, and that it weighs ~100lbs less than a bonnie. They are tall and ugly comparitively, and the factory did not install any of the soul that comes with the bonnie.

Anyway, my buddy isn't into modding but he loves trash-talking my bonnie. Anytime I get a new part he says, "yeah, well can it beat my bike?" and up until recently we were dead even on a flat-out race, maybe with him pulling ahead towards the end. Light to light I have him beat.

I haven't raced him since I added 790 cams and the D&D 2-1 and I think I have the upper hand now. I'm almost certain once I get the 813 cams and modded ignition box I'll have him stone cold beaten.

Cost? He bought his bike used with 900 miles on it for about $5500. I have about that much in mods! I win though, because his bike is ugly and disappears in a parking lot.
 

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and back on topic, with EFI (and megasquirt) you could run HUGE throttle bodies on a bonnie, somewhere in the neighborhood of 43-45mm or better. I'm remembering here, and maybe mis-remembering (Roger Clemens used that term today on TV), Jorgen saying something about with the EFI you can run bigger throttle bodies than carbs and not lose power on the bottom end and gain it on the top end.

here's one of Jorgen's turbo/efi bonnies:

http://www.stabbarps-auto.com/welcome.html

Bonneville 2002 Turbo

Megasquirt EFI

120HP at the wheel

Best ET 6.66s at 1/8 mile









 

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Discussion Starter · #8 ·
yeah...about that....

I have a buddy, he rides a bone-stock (down to the silencer) sv650. I think it's a 2007. It's EFI. It is boooo-ring to ride. No vibes at all, no feedback, very little power until 6,000 rpms then it's a race to redline. It does come alive on top but it's dead on bottom. A few plusses over the bonnie are that it is dead smooth cruising at hwy speeds in 6th gear, and that it weighs ~100lbs less than a bonnie. They are tall and ugly comparitively, and the factory did not install any of the soul that comes with the bonnie.

Anyway, my buddy isn't into modding but he loves trash-talking my bonnie. Anytime I get a new part he says, "yeah, well can it beat my bike?" and up until recently we were dead even on a flat-out race, maybe with him pulling ahead towards the end. Light to light I have him beat.

I haven't raced him since I added 790 cams and the D&D 2-1 and I think I have the upper hand now. I'm almost certain once I get the 813 cams and modded ignition box I'll have him stone cold beaten.

Cost? He bought his bike used with 900 miles on it for about $5500. I have about that much in mods! I win though, because his bike is ugly and disappears in a parking lot.
Excellent! I was trying to be 'kind' in NOT saying the SV is as ugly as a mud fence...just in case someone here owns one. It's just a bike without any charisma IMHO. It is impressive how well it runs stock though, mid 11 sec quarter miles and zero-60 about 3.6 seconds. Takes a lot of motor work on an 865 to get to this level...partly due to weight, which surprisingly is only about 50 lbs wet difference between the two, according to two reviews I've read. From your impromptu racing with your friend, it sounds like you could be in the mid 11 sec range in the 1/4 mile!! (Stock Thrux is 13.3 sec @ 100mph) Get out there and get some drag slips!

Don't get me wrong...I have never wanted to own an SV650, although I'm sure they are fine motorbike. (I did ride a TL1000S once and it was a monster engine) Just pointing out how such a small, stock engine can pack such a punch.

But... like you said....just park your bike next to your buddy's SV, and which one do people gravitate towards with smiles on their faces? Hmmm, lemme guess!!

Cheers,
BLIGHT
 

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Whoa, sweat. Nice find.

Yeah. The big benefit of EFI in performance applications isn't the numbers up top, but rather that you can use it to bring the bottom end back around when you go crazy up top. Big power still takes big bores, long cranks, ported heads, oversized valves, and lumpy cams. All of this makes the bike run like crap down low and an absolute nightmare to start, because the carbs are dependent on intake vacuum to meter and emulsify the fuel correctly, and there's very little intake vacuum with a setup like that. EFI fixes that, because fuel metering is in no longer in any way tied to intake vacuum. As long as there's some intake vacuum to suck the fuel emulsion into the chamber, the bike will run. For the same reason, you can use really big throttle bodies- like 45s- even on relatively mild engines. It won't idle like a bike right off the showroom floor, but it will behave itself reasonably well, and you won't have to run it up to 6000 rpms to launch it without having it fall flat on its face.

If the Scrambler gets too ornery, it might get slapped with a MegaSquirt at some point. Other projects have me distracted at present, though.
 
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