The 3.2 SS Carb dilema

[coomo]

Ok guys thoughts...
Recently a 3.0 engine which was modified to a 3.2SS sold.It was from a respected 911 performance company.
Bear in mind,this was a UK car,with Larger ports.
It was a standard "text book" build with 964 cams,high comp pistons.Weber IDA3C carbs.
This engine dyno at 230ft lbs torque.260BHP.
Thats very good numbers,for a low cost 3.2SS build
Heres the kicker.These were custom carbs.Original 40mm bore to 44mm.
The usual fitment or bore would have been 46mm.
However the guys who did the build speced only 44mm.
Perhaps the increased velocity,of the slightly smaller bores, helped to get this build to a very healthy 260hp? Thoughts....

[76dno]

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[icarp]

The TQ number is the healthy high number , at what rpm for the tq and hp
The weber conversion is a normal conversion, what size chokes ?
Ian

[roblav]

Sounds like with 964 cams, the builder was looking for more lower rpm torque rather than higher rpm HP. Looks like he succeeded. The lower rpm engine will benefit from smaller bore carbs, ensuring a greater vacuum, or lower pressure, at the jets. An S or mod S cam would pair better with 46 bore.

[Jeff Alton]

Is this measured at the flywheel on and engine dyno or WHP on a "rolling road dyno"?

Cheers

[Zuffenwerker]

Wow very strong numbers that’s impressive. It would be interesting to put the car on a chassis dyno just to see how much power is actually lost. I know 15-20% is the common thought

[CBA]

Seems like an ambitious dyno machine was used to produce those numbers… look forward to hearing what you find out.

[stownsen914]

I'd guess you wouldn't notice much difference between 44 mm and 46 mm carbs.

[Dpmulvan]

Originally Posted by stownsen914

I'd guess you wouldn't notice much difference between 44 mm and 46 mm carbs.

+1 it’s a lot more complicated than 2mm on carbs or large ports.

[coomo]

Thanks for reply guys.Its interesting.Unfortunately,no more details are known at this time.Ill try and dig a bit further.

[Jeff Alton]

Originally Posted by CBA

Seems like an ambitious dyno machine was used to produce those numbers… look forward to hearing what you find out.

Every UK dyno I have seen numbers from over the last 35 years is ambitious. That said, the peak "number" is not important, the change from stock or known baseline data is what is important.

Cheers

[coomo]

Originally Posted by Jeff Alton

Every UK dyno I have seen numbers from over the last 35 years is ambitious. That said, the peak "number" is not important, the change from stock or known baseline data is what is important.

Cheers

Hi Jeff.
I looked at post on DDK again.The builders were selling 5/6 engines.Plus its a few years old.I stumbled on it by chance,whilst perusing ads.That said Tech 9 the builder/seller have a good name.
Of course Dyno numbers arent always what they seem,and I respect your input greatly.
My original point,was concerning the boring of the carbs,and as to whether the slightly smaller bore could increase velocity,and combustion?
I have noticed a disparity between carb size used in UK and USA.
Whereas a USA builder,will tend to use 46mm (pmo for instance) Over here many use 40mm.Not saying anyone is right or wrong.Just different.

[rory gallagher]

Please correct me if this is bad form.
I can't comment on your modified carbs but some of the info here applies to my current project.
I have a 3.2 SS and want to use the practically new 40s that I already own.
I have a great selection of jets, ACs,emulsions etc. and 34 and 36 vents
I hope to get info on a known combination as a good starting point.
I'm encouraged knowing that these carbs are used successfully in Europe
Engine specs....
large ports, DC60, S spec dizzy, Mahle 98mm PCs 9.8 to 1
TIA
Rory

[Jeff Alton]

Originally Posted by coomo

Hi Jeff.
I looked at post on DDK again.The builders were selling 5/6 engines.Plus its a few years old.I stumbled on it by chance,whilst perusing ads.That said Tech 9 the builder/seller have a good name.
Of course Dyno numbers arent always what they seem,and I respect your input greatly.
My original point,was concerning the boring of the carbs,and as to whether the slightly smaller bore could increase velocity,and combustion?
I have noticed a disparity between carb size used in UK and USA.
Whereas a USA builder,will tend to use 46mm (pmo for instance) Over here many use 40mm.Not saying anyone is right or wrong.Just different.

You did have odd sized carbs. Not sure why the shop thought the effort and expense was a good choice. But, to each their own.

Peak dyno numbers are not important, it is a tool to tune with. If you are happy with the performance, that is ALL that matters.

Cheers