Engine performance - Wrist Twisters
 
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post #1 of 14 Old 09-16-2012, 01:29 PM Thread Starter
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Engine performance

I am currently replacing the head gasket with a thinner one to bump the compression a little (ala the touring919 setup).

As long as I have the head off, I wanted to see if anyone knows of anything that can be done to the head or air intake to tweak the power a little. The current mods include flapper valve and 900rr exhaust.

I've been in here a while, and I'm aware of the standard feedback (power commander, can't do it, you will lose your torque, lose weight, run with a half empty tank, buy another bike, etc).

That being said, anyone know of other options ?

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post #2 of 14 Old 09-16-2012, 03:34 PM
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post #3 of 14 Old 09-16-2012, 04:50 PM
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the 919 is hard to make more power out of... just ask bucky.... he went so far to have custom pistons for a slightly bored out motor (945ish cc if i remember), modded head with 900RR cams custom degree dialed in, 900rr exhaust, power commander... and he was only making about 120ish at the rear wheel. (before the NOS of course)

Only other real option is a Turbo, but dont attempt to run over ~ 7psi of boost because you will stretch the head bolts and dump exhaust into the cooling system.


really if your looking for big power, i hate to say it but the 919 is not going to be the bike for you. Unless you go with the juice or turbo, there is going to be no easy way short of running a full 900RR motor in the 919 frame.

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post #4 of 14 Old 09-16-2012, 05:41 PM
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Quote:
Originally Posted by RichT
I am currently replacing the head gasket with a thinner one to bump the compression a little (ala the touring919 setup).
What's the advantage of raising the compression? (Not being sarcastic, promise.)

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post #5 of 14 Old 09-16-2012, 05:56 PM Thread Starter
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Originally Posted by 2002-919 View Post
What's the advantage of raising the compression? (Not being sarcastic, promise.)
In general, a little more horsepower. Check out some of the older threads from touring919 where he seemed to have gotten 118 of of his 919 with a mild port and a little more compression. https://www.wristtwisters.com/forums/...mods-5509.html

I don't know if its in this thread, but he did have before and after dyno charts.

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post #6 of 14 Old 09-16-2012, 06:00 PM Thread Starter
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Quote:
Originally Posted by nd4spdbh View Post
the 919 is hard to make more power out of...

really if your looking for big power, i hate to say it but the 919 is not going to be the bike for you ...
Not looking for massive power, just a slight tweak to the existing setup.

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post #7 of 14 Old 09-16-2012, 07:21 PM
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well good luck with it...

Not sure why one would open up a perfectly good rock solid 919 motor in chase of a couple hp that probably arnt there. But to each his own.

The main problem with making HP on the 919 is the relatively small throttle bodies.... which keep air velocity up at lower rpms for better power and tq down low.

Im not saying extra hp cant be found, but it aint easy or cheap.

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post #8 of 14 Old 09-17-2012, 12:19 PM
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post #9 of 14 Old 09-17-2012, 12:38 PM
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Quote:
Originally Posted by nd4spdbh View Post
Not sure why one would open up a perfectly good rock solid 919 motor in chase of a couple hp that probably arnt there. But to each his own.
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post #10 of 14 Old 09-17-2012, 12:58 PM
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Quote:
Originally Posted by RichT View Post
In general, a little more horsepower. Check out some of the older threads from touring919 where he seemed to have gotten 118 of of his 919 with a mild port and a little more compression. https://www.wristtwisters.com/forums/...mods-5509.html

I don't know if its in this thread, but he did have before and after dyno charts.
VERY interesting thread! Never changed a head gasket on a car or moto, how skilled of a mech do you have to be? 12hp gains is impressive

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post #11 of 14 Old 09-17-2012, 01:06 PM
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Quote:
Originally Posted by andrewebay1 View Post
VERY interesting thread! Never changed a head gasket on a car or moto, how skilled of a mech do you have to be?
you really dont have to be super skilled, but you do need to be methodical and know what you are doing.

taking the head off would require removing all intake (throttle boddies, airbox etc) as well as header, draining of coolant and probably removal of radiator.

Its no small job on the 919, or any motorcycle with overhead cams, especially for the small possibility of minimal horsepower increases.

Typically one will run a thinner head gasket / deck the head and or cylinders, in combination with other mods (hotter cams, cam timing, ignition timing and fuel mapping) to get moderate increases in horsepower... but just a thinner head gasket in general wont do to much, especially on the 919 which its mild cams and small throttle bodies.

Really and honestly the 919 tops out as far as speed wise at speeds WAY WAY to fast for street use... if you want the feeling of extra power, just drop one tooth in the front... walla instant power that doesnt require messing up a perfectly good motor.

12hp gains are nothing to go crazy over IMO... thats only ~ 10% increase, at the sacrafice of actual street power (low to mid range), now if it was making 10% more across the board then ya go for it... but its not especially with retarded cams.

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post #12 of 14 Old 09-17-2012, 01:11 PM
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Check the thread out dude, Rob and a few others have an excellent explanation (pg 2). I'd probably be way in over my head but for the more inclined, it's worth a look.

Stock gasket from Robs measurements is around 83mm.
Here are thinner sandwich type gaskets from Cometic that range from 72 to 75mm:
http://www.shopengineparts.com/parts...%29&type=model

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post #13 of 14 Old 09-17-2012, 01:15 PM
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"What's the advantage of raising the compression? (Not being sarcastic, promise.)"
My understanding is that you get a more complete burn of the fuel air mixture. Slightly more power, slight more engine efficiency (better mpg.) You'll also run an increased risk of preignition or detonation, which can be addressed by running a hugher octane fuel.

I wouldn't mind bumping my CR up to the point where running premium was required, I think it would be interesting to see what the power and mpg gains were like.

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post #14 of 14 Old 09-17-2012, 01:37 PM
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Boco, there's a dyno graph in a PDF link on page 2. THat's with port (no polish) and a thinner gasket. Rob Tharlson has a post with numbers on compression changes with different levels to the mod (gasket change only, gasket + port, etc) on pg 2 as well.


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----------------
------------
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- '01 RC51 SP1 (Sold)
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"Security is mostly a superstition, it does not exist in nature: avoiding danger in the long run is no safer than outright being exposed. Life is either a daring adventure or nothing."-Helen Keller
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