Optimal Carb Size for a 96" and 103"

[blk-betty]

What is optimal carb size if moving up from an stock 88" to either a 96" or 103".

I may be in a situation where I need to replace my 88" crank and debating just going bigger but want to keep parts and $$ to a minimum.  How big will of a motor will the stock CV 40 suppot assuming a low compression low-mid range tq build?

[mayor]

Mark,
that will depend on what your heads are capable of flowing.  The stock heads become your limiting factor in flow abilities since the stock Cv40 will cover the stock '06 heads just fine.  I posted a study that Bruce did on various carbs in the Tech Tips section.   The carb can become a limiting factor when running ported heads. 

[blk-betty]

Thanks Mike

Heads are 06 will be left untouched.  I really hope I don't have a major problem but if I do I want to keep costs to a minimum, ie rebuild with stock 88" crank or stroker crank that comes stock in a 96" and if it needs cylinders/pistons then I would go 103" but can't see why it would need cylinders/pistons.  been down this road before and the more hi-po stuff you add the more $$ such as carb, ignition cams, etc.

Anyone know if the stock 88" cams were used on the 96" motors?  In other words if I go stroker crank can I just have it put back together as is?

[mayor]

I'm pretty sure the stock 96" cams are much different (and earlier intake close) than the stock 88" cams.  You should be fine though.  Use a .030" head gasket and your static will work out pretty close to 9:1 corrected.   

back to the carb discusion.  Bruce reported the Cv40 flows 131cfm (10") on the manifold, John Sachs reported (on an old HTT thred back in late '05) the '06 heads flowed about 126 cfm (10", although John reported it as 211 at 28").  Factor in loss do to AC, and it may be a toss up. 

[Velocity1]

What is optimal carb size if moving up from an stock 88" to either a 96" or 103".

I may be in a situation where I need to replace my 88" crank and debating just going bigger but want to keep parts and $$ to a minimum.  How big will of a motor will the stock CV 40 suppot assuming a low compression low-mid range tq build?

As stated, you're planning a "low compression, low - mid range torque build".  

For example, If you're planning on a 95" Andrews 37G build for example, (which is what I'm running now), compression is 9.8:1, and my '02 heads have had a better than average street port done on them.  My tweaked CV40 has been extremely tunable to support the motor's build requirements.  I'm using the SE intake, Pro Pipe with custom torque plug and both a DTT and/or SE ignition, a Ness Big Sucker Aircleaner with the Zippers larger K&N filter.  The results are extremely impressive for a relatively low compression motor in this configuration on my Softail.  Obviously results will vary based on your A/C and exhaust type choices.

The CV40 produces excellent velocity and works nicely in this application.  I'm currently running a Wood 415 carb, but have (2) almost identical 40's that I assembled, and would put them up against the 415 on the Dyno.  Changing from my 40 to the Wood is seemless when measured with the "SOTP" dyno, and there are no driveability issues what so ever with either carb.  

Of course, I believe, the Wood carb. is better prepared to support larger ci. motors due to its larger venturi.  

To answer your specific question, personally, I would work with your current CV40 for the build you've planned, first, rather than spend unnecessary $$ for a "miracle in a box" carb.

I'm just throwing this out there for a real world comparrasion build.

Good luck.

V1

[Sonny S.]

Even though the CV40 will be enough for a mild 88 or 95/96. The CV44 will give you more on top, and won't take anything from the bottom.
Going 103, use the 44.

V1, have you had your bike on the dyno ?

JMHO
Sonny

[jsachs1]

Blk-Betty,
Cut to the chase and put a 45 Mikuni on it.It won't hurt bottom end on a 95" motor,and will be enough for a 103".
John

[blk-betty]

John

I'm trying to keep my little 88" and everyone is doing all they can to convince me to go as big as possible.

If I do infact have a crank issue I'll have to make a decsion at that time what I'm going to do but I have to keep costs to the minimum.  With the economy don't know how secure wife and my job is, know what I mean>

If I gotta get a new crank or have mine fixed, care to give a recommendation on where to go for that kind of work?

[HD99FXR3]

Hey Mark,
             If you put a 96" crank in you are going to have to change pistons, because of wrist pin location. Which in turn means you are going to have to bore the cylinders at least .005 over. Which costs the same as boring to size for a 103".

By the time it's all said and done you'd be better off pulling the complete motor yourself, and sending it in for a rebuild. That way you can stay stock like you said you would.   

[blk-betty]

HD99FXR3

Thanks for the info.  Someone finally gave me some advice that sheds light on my delimmna.  Guess I was wanting it to be easy just to swap for a 96 crank and be done with it.

Well now just gotta see what the problem is then decide on how deep to go to fix it.