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Discussion Starter · #1 ·
I put my new 904 on the dyno today found out I was way lean on the main jets.Was not a good air day 29.8 air pressure 80 deg but the little motor still ran good.84.67 hp and 63.89 ft/lbs. Here is the dyno run the graph has some missing peaces but you can connect the lines and tell what its doing.If any of you phto guys can fix it please do.

I found out today how well the 813 cams work in my new tpusa 904.I had it on the dyno today and found out I have it way to lean on the main jets.These cams have as flat a torque curve from 5000 rpm to 8400 rpm as I have ever seen.When it hit the 8400 rpm rev limt it was still picking up hp.I posted the run in the dyno section.I think with the right jets on a good day with a 9000 rev limit it will be as fast as my 989 was. With a 14.1 a/f mix it made 84.67 hp and 63.89 ft/lbs sae 1.0 c/f .
The motor has a tpusa 904 kit ,tpusa 813 cams,2mm oversized valves ported head,42mm mikuni carbs,D&D 2INTO1 PIPES,procom box,carrilo rods.
 

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Mike - I marvel at how much you know about these bikes, and motors in general. While I try to keep up with the info you and so many others post on this forum, I sometimes find myself sitting and reading in awe at the vast knowledge that you have undoubtedly accrued through years of experience.....

even if I have absolutely NO idea what you're talking about most of the time.

Congrats on the upgrades is all I can think of to say.

Cheers
 

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Looks like good numbers to me - not an expert for sure, but the power curve looks pretty smooth, even if you are a bit lean. A bit more power to be picked up by straightening the a/f out maybe?

Very impressive I think.
 

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Good work and good results Mike!
Well done.
And as you say, if you get that A/F trace down a little there's sure to be more to be had!


V.
 

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Great Stuff Mike. Congrats and thanks for sharing with us. You will be the man I will come to for advice when I pull my Bonnie motor apart.
Must be a rush to ride,
George
PS: On an EFI bike, I wonder how much hp I would give up to your 42mm carbs?
I know this isn't known at this point...
 

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PS: On an EFI bike, I wonder how much hp I would give up to your 42mm carbs?
I know this isn't known at this point...
probably 5-10 hp. EFI is good, but the throttle bodies are the same size as the stock bonnie carbs and they can only flow so much. The real benefit of EFI is that you could install larger throttle bodies (bigger than the 42mm mikunis) and they'd still fuel well at low rpms. I bet you could go as big as 45mm or 47mm, but that's just a guess.
 

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Probably right sweat. Increase the size of the pump...need to decrease restriction into the pump. :) Higher flowrate injectors are also available but likely an air and not fuel deficit as you say.
Things get expensive fast on these motors as you know. Throwing new throttle bodies into the mix really increases the ante and why I asked.
The other question is...if going nikasil BB kit + 813 cams and sticking with stock throttle bodies...maybe it doesn't make sense to port and polish the head and in particular increase valve size since pushing fractionally less air through the motor.
Thanks,
George
 

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I think you should put bigger throttle bodies on, do the big bore and cams and port and polish George, and then write an excellent "how to" for all the EFI motorheads that are coming along!

:thumbsup:
 

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I'll probably never attempt to wring that kind of power out of my Triumph - but it's nice to know that it can be done...

Thanks for sharing all the great info!
 

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you can get bigger throttle bodies from another EFI bike and make them work. How? dunno!
Me either but no doubt this will be figured out in ensuing months as these bikes get into more hands and further hotrodding options explored. Mike also mentioned that the throttle bodies may have room to be bored out a bit which may give the EFI motor more legs for building. One of the things we have kind of learned is there is always a weak link. Grow one thing or two and the weak links are further exposed.
George
 

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Discussion Starter · #14 ·
I think in the next few years you will see some wild things done with efi bikes.If you get the flow up they should make the hp the carb bikes make.when it comes to intake flow everything should match up .Heads ,cams ,carbs or throttle body is where hp is made on these motors.You can make alot more torque then stock with out haveing to big of carbs or throttle body but for these motors to run over 8000 rpms where the hp hides you need all the flow you can get.Later this year I will have a bigger head with bigger cams that I want to put on the 904 to see how much hp I can make.I think you can go over 90 hp if you turn them 9000rpm with the right head and cams.
 

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you can get bigger throttle bodies from another EFI bike and make them work. How? dunno!
I think Jojje knows how to do. Send him a message.
Erich
 

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Looks good Mike!!! I wonder how much of that HP is due to the 2:1's. I also wonder how much difference the 11.5:1 vs 10.5:1 compression makes. I would think it would have more effect on the torque than the HP.
 

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Discussion Starter · #19 ·
Looks good Mike!!! I wonder how much of that HP is due to the 2:1's. I also wonder how much difference the 11.5:1 vs 10.5:1 compression makes. I would think it would have more effect on the torque than the HP.
The 2into1 adds 5 to 10 hp from what I have seen but they move the power up in rpm range .I think the extra comp. works damn good with the better cams,cams kill running comp.I put the next biiger jet in it after the dyno it feels stronger on top now.The torque curve is so flat from 5000 on .It fools me on the high way if I am not watching the tach I will be in 4th gear and think I am in 5th its more like a jap bike at cruse speed pick a gear and go lol.
Man will it ever stop raining so we can get together and ride some.lately weather has been so screwy I been scared to ride very far.
 

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cams kill running comp.
Maybe you should clarify that statement Mike?

Performance cams only hurt dynamic compression at lower RPM's due to poor cylinder filling which is caused mainly by high overlap.

Performance cams actually increase dynamic compression at higher RPM's due to improved cylinder filling, this afterall is where the performance gain comes from - increased volumetric efficiency. ;)
 
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