IDA venturi size with JPM heads

[neil68]

Just installed a set of JPM MS230 heads on my 2332 cc Beetle engine.  I'm running some older Italian 48 IDA's with 42 mm venturies currently, but also have a spare set of 45 mm IDA vents that I picked up a couple years ago, but have never used.

The JPM heads have 48 x 38 valves, so I'm thinking that larger venturies might work well for racing the 1/4-mile.  However, does this only work for the bored out 51.5 mm IDA's, or is it worth a try in the standard 48 IDA's?

Any feedback on your experience would be appreciated.

Thanks!

[TexasTom]

How far/high do you want it to rev?
What cam/valvetrain are you running?
The venturi size is directly linked to the rpm range a specific size motor will or is to run, not necessarily the size of the intake valve or carb.

V = 20 * sq.root(cyl-vol/1000 * max-rpm/1000)
for a 2332 and 8000rpm ...

V = 20 * sq.root(.583 *
V = 43.19 mm

A 45mm vent should be good for close to 8700 rpm, don't know how drivable it will be on the street though.
Hope this helps,
TxT

[neil68]

Thanks, Tom.

I haven't put this combo on the chassis dyno yet to look at the power and torque curves.

I was using a 7300 rpm rev limiter with the previous 44 x 37.5 heads, but the JPM springs can rev higher, so I'll have to experiment a bit.  I think I'll stay with the 42 mm vents for now.  There's something to be said for smoother street driving as well...

[TexasTom]

Neil,
Are you running a JPM/Raptor cam as well? They're the BOMB ... very easy on the springs.
I have a couple going in some current builds ... you can see the difference degreeing the cam in, very smooth action.
Lucky Dog to have a chassis dyno available ...
TxT

[neil68]

Currently running my previous Web 226 camshaft (similar to the FK87) and Becker lifters.  This cam has 278 degrees (0.050") and total lift is 0.570" with my current rocker set...

[H67bug]

I run Raptor cam with Comp Elim heads 44 x 38 valves.

A dyno helped set it up correctly.

Car ran best with slightly smaller chokes than initially had been suggested. Went from 46 to 44 (51.5 IDA).

Did not try smaller than that as ran out of sizes to try.

42 sounds small.

If you have invested in such a motor, unless you are a wizz with the LM1, some dyno tyime is a wise investment.

Enjoy!

[Fasterbrit]

Gyles' motor runs a similar spec motor with 44mm vents on 48s. Runs beautifully on the street - no low speed running issues and runs 12.5 quarters on treads in a full-weight streeter. I would suggest the 44s would work no probs. It will give you the extra top end edge . You have the cc to ensure the signal to the carbs is strong, even lower down the rpm range.

[Chris bugster]

I used to run 44mm vents in 51IDAs in a 2386cc. It pulled nicely to just past 8000rpm from about 4000 in 4th gear and then felt flat. The heads were 48x38 comp Elim and the cam was FK89.