Bonneville America Forums Forums Technical Forums Performance Mods Power Upgrade or Torque Upgrade?

2007 America

I'm ready to make the move to punch out my bike.

But,,,,,,,do I go for torque, or power.

The 865 HO kit can give 30 horsies with similar set up as per Zmillins

OR

A 904 kit, which will give me bottom end Grunt.
I'm assuming the 904 is a torque machine.
The 865 HO is a power monger.

Which is more durable?
Which is more fun?

Well this is a start,,

Remember, Z's 865HO also has head work.
Think about the RPM band where you normally ride.
IMO, if the cylinders are coming off, it's gonna be for a 904.

Durable vs. fun or both. I say both. I swear by TPUSA and their support is awesome.
When using my set up for comparison keep in mind I also have carbs, cams and igniter.

You wont go wrong either way but one thing is for sure...
The 904 will give you more tourqe.
The HC kit will give you more power.

Both can be done as standalone mods but both will be so much better with carbs/headwork.

Ask Marty how his bike is before and after carbs with the 904. He recently added the FCRs. BTW... I don't know if he had headwork or not.

Both are about the same amount of work, meaning your getting down to the jugs. The HC kit comes with cams so it can also be upgraded to a BB later but really why not go to a 994 (my plan) if you already have the cams.

I know... not any real advice and truth be told for as long as I debated all this it was a fluke I went with the HC kit BUT I was so pleasantly surprised and for as bad as I really want to to the 994 Im think I might be sticking with the current set up for one more season. I have a wedding to pay for first and a car payment again. Im glad I did what I did cause that bike is a beast.

If you take anything away form this... go to TPUSA and talk to Carlos.

I meant if you do the HC kit and upgrade to a BB down the road.
An EFI owner did a 994 and got similar HP (83) but more Tq (63 vs my 55).
That was with only the BB, no cams. Granted it was EFI so fuel could be adjusted easier but still limited to injector size. Hence the need for the other goodies on a carb bike.

994 EFI BB

I would go the 904 with the FCR. I rode Martys after he put the carbs on, he did not do any head work and that things goes like jack the bear! Pulls all the way through the rpm range in every gear....uhm and yes i was a smilin! So much so i was chocked to get back on my bike afterwards, i think he took some pleasure in that! LOL I will be doing the 904 with the fcr carbs for sure when i make the change.

I normally ride in the lower end of the rpm range and nail it after a shift to speed limit,,, +/-.

Although, It is fun to get it in the power band and feel an endless type of pull,,,,,,,

I joke at work that I plan on taking a big road trip on the weekend. When they ask where, I say, Falls or Plymouth(12 to 20 miles). I get the laugh or eye roll, then are told that I live in a vacuum.

So is the 904 MY wiser choice?
Is 11.5 to 1 Compression Ratio hard on the motor life.

We have similar riding styles.
In all my research and taking into consideration that I keep my RPMs lower I knew I needed a torque machine vs a power machine (that and Im kind of a fat arse).

My intent was always to do at least a 994 BUT I also knew that to get what I wanted out of it I needed to get the engine capable of breathing. I chose to do do carbs, cams before the BB knowing I would get minimal gains but be ready for the heavy work the next season. The only reason I did the HC kit and head work was due to my little snafu with my cams.I was mistakenly shipped the HC pistons and gaskets (I was going to return them). Since I needed all the gaskets and pistons were there looking all shiny and sexy I opted to install it all while the head was out getting the valves fixed and since they were doing that then why not port/polish. Now that you know why I went in the seemingly opposite direction of my goal and why I am about to contradict what I actually did here is some more info to think about.

If I was on a budget and could only do one thing for the next year I would do the 904 for the torque increase alone BUT only if the results would fit my riding style. This was not something I did enough research on and got lucky with my setup.
I still wish I could make more torque at a little less RPM... like 2500rpm or even 2K (right now I'm at about 50ft lb at 3K with a peak at 55ft lb at about 3800rpm). What makes me grin is that over 3k all the way to red line it never drops below 50ft lb. I also don't know if its really possible to make bigger torque numbers at lower RPM due to the motors nature (P twin vs V twin).

NOW... what I can not answer (but I'm sure Carlos can) is where the 904 starts to make torque. This is as important as knowing your goals based on riding style. You see... if you make good torque numbers but they don't come in till say 4K then its not suitable to your riding style.
On the other hand if the torque starts to come in at say 3K (like mine does) then its a different story. BTW... don't kid yourself by thinking 3K and 4K are close enough together. Ride your bike for a few hundred miles and pay attention to where you keep your RPMs. Where you shift. Where you are when you downshift. etc...

So whats my point in all my rambling...
1 - know what you really want to achieve.
2 - talk to a pro about your best options to achieve #1.
3 - create a plan to do it in stages that make sense or dump a lot of money and just get it done.
4 - keep us in the loop,post lots of pics and enjoy it!

Almost forgot... 904 with 11.5:1 should be very street able. But this is also another point of research...
If you plan on doing head work (bigger valves) make sure the kit you use will accept bigger valves. I know the current TPUSA kit will (based on the website description) but others wont. Ask Marty... hes going nuts with this scenario.

I hope my rambling will help you make an educated decision

i have the 904 kit...other than a little vavle rattle at the top end, i love it.

Sorry people,,,,,I got busted.

My boss will not let that type of investment happen.
Looks like "TPUSA" FCR 39's are OK'd(I have to go to a baby shower as part of the deal).

I apologize for getting hopes up. It sucks even more here.

AND YES,,,,,,,,,,,,,I Only wear the pants in my house, When she's not home!

The average person knows that ya don't mess with 5'6", 115lbs with RED HAIR

THE DOORS ARE OPEN FOR RAG-OLA

something is better than nothing. You know... christmas is coming up.

good read here performance mod similar what Zdenko did

These are relatively low revving engines. 8,000-8500 rpm with appropriate mods.

Go for the torque.

Horsepower is for advertising, torque wins races.

HP = Torque x RPM ÷ 5252

That is; torque is the constant. HP is a figure derived from the torque which is a measurable unit of work: Force times distance.

For engines, torque and horsepower will ALWAYS be the same number at 5252 rpm.

That constant applies to electric motors as well.

Here's a good article http://www.lainefamily.com/hp.htm