Cam choice for carbed 3.2 engine
 

Hi,

I am rebuilding my US spec 3.2 Carrera engine. I will use carbs on this engine, since I didnt get the Motronic system with it.

It was going to be a stock rebuild, but now it seems like the cams need reconditioning, and the pistons may have too big ring gaps. So, nowI have the possibillity to

1. regrind cams
2. buy JE 10.5 pistons

Could anyone please recommend a cam profile for me? Or should I just re-finish the Carrera profile? Should I use different cams depending on the piston choice?


Regards,

Johan

A lot of what you put in depends on what the engine is for. Are you building a street engine or is your engine for track use. If it's dual, maybe something like a 3.6l grind may be what you are looking for.

Ok, the 964 one?

This is for a street car, but a hotrod. So the ideal cam choice would work with the low comp 9,3:1 US pistons and carbs. I would like a track car feel, but cant rev more than 7k rpm's due to the weak rods. I am NOT looking for a bus engine feel, like the 3.0 SC with all the power around 3k rpm.

I might purchase 10,5:1 JE pistons anyway if that would allow me to change to a better cam.

Any thoughts would be very appreciated!


Thanks,

Johan

Johan,

Stock pistons restrict your cam choices to something like a 964 grind. There simply is insufficient clearance for anything more.

If you are willing to change pistons, you have far more choices for how you will use the car. I would simply advise the temptation to over-cam it unless you install close-ratio gears. A Mod-S cam is a good one for such applications.

If you install JE's, be very careful about your CR unless you run twin-ignition. Florida weather is hot and anything over 10:1 on pump gas in your climate requires some compromise in ignition timing which makes for a lazy-feeling engine and less performance.

Wecam makes a pretty incredible cam for this application. Harry Webber designed it back in the 70s and it has survived the test of time. 2021 is the cam designation.
It fits the stock engine with regards to piston clearance.
You can also cut pockets in your stock pistons creating clearance for a plethora of cam choices. The loss of compression is negligible. At that point I would go with the DC 40.


This is a 2.7 piston but you get the idea.
http://forums.pelicanparts.com/uploa...1390242955.jpg

I used JE pistons @ 10.5:1 with 46 Webers, twin plug and GE 60 cams. Exceptional power and very street-able. You won't be disappointed.http://forums.pelicanparts.com/uploa...1390258992.jpg

Did you ever have the motor dyno'd?


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247 rwhp

Many thanks for the answers!

Wow Lindy, nice! Are there any other mods to the heads except the twin plugs? How is the engine character?

I have the car in Sweden, so it is unfortunately very cold here and I believe we have better fuel as well. Am I right to think 10,5 would be ok since the Euro 3.2 has 10,3?

Regards,

Johan

Just checked ebay and a complete 10.5:1 JE piston kit is $980. I am guessing just the ring kit for the OEM pistons are around $300. Seems like a good deal to widen the cam choice!


Johan

My build was based on a '78 SC 3.0 litre. Heads are bone stock except racing springs and retainers.

The engine runs just like stock below 3500 and really comes on at 4500-5000 pulling easily to 7000. It is a blast to drive. Have surprised many 5.0 Mustangs and Corvettes. It will spin 275-35-17 rear tires shifting to second but it's a little hard on the transaxle.

http://forums.pelicanparts.com/uploa...1390319741.jpghttp://forums.pelicanparts.com/uploa...1390319795.jpg

If you go with JE, get them from someone who knows the product (Steve, Henry, LN Engineering, EBS Racing, etc.) that can make sure the size you get is correct. Meaning, you don't just buy a set of 95mm pistons and throw them in the cyls. You need to know your exact cyl bore diameters so the JE pistons can be sized accordingly to get the proper, accurate piston skirt clearance.

I have the same setup except running twin plug motronic, don't know if this cam works well with carbs but it sure does with my setup: dc-21 aka super cup

Does anyone know the valve lift limitation for valve/piston clearance and valve spring coil bind for the Motronic pistons and stock valve springs?

Dougherty recommended his 993SS profile to me for a hot 3.2, but I'm unclear as to what would need to be upgraded along with them.

+1 to Henry.

Get the DC40s and do it right with the pistons. From there you can build the rest off of that foundation.

I did this with my 3.0-now-3.2ss very similar to what you described...

It's a street car. single plugged, 93 pump gas. 9:8 JEs, 46PMOs. Pretty much everything you are looking at with a few extras you'll wind up wanting anyway. Headers, little head work...

Got to the dyno for the first time this morning to dial it in and got 253hp 226tq-yes at the wheels. Happy. I'm going to start a thread tomorrow labeled "3.0 to 3.2ss with before and after Dyno" with the full story and scans. Scans will of course show where exactly in the rpm range the power comes on so you'll be able to see the cam piston combo power band right from my dyno charts.

Wow, that are some very nice numbers! Congratulations!


Regards,

Johan