Cam advice for 3.2 SS being upgrade from CIS to ITB EFI

[tommott]

Hi all,

I'm contemplating a cam swap while I have the motor out of my car for a CIS to the RHD ITB/EFI swap by way of Al at X-faktory. The motor is originally a 3.0 built up to a 3.2 SS with 98mm pistons and cylinders. It is a '78 motor with the large port heads, has SSI exhaust, and has run with the stock SC cams and CIS injection since the motor was first built in 1987. The new ITBs will be run by Megasquirt and ignition by MSD streetfire.

I've done a bunch of searching around the forum and there is a copious amount of info on 3.2ss, cams, etc but I am not finding much info as to what specific cams work with the 98mm CIS pistons. Anybody have a run down of what cams will work and/or recommendations? I see a lot on the GE 40 cams for this setup, but spoke to Dougherty Cams and it didn't sound like the GE 40 cams would clear the 98MM CIS pistons. He recommended the 993 stage 2 cams.

The car will be a street hot rod and will see a lot of spirited driving in the NC mountains, living down the street from the tail of the dragon. Obviously more HP is wanted but still want to have enough grunt in the midrange to pull out of all the endless corners up there. An optimal powerband for an auto-x type/hill climb type car will should work best for my needs.

Thanks

[MichaelSJackson]

Google "993SS 3.2SS" and you'll find a lot of owners happy with the Dougherty cams in your configuration.

Or Google "993SS 3.2SS Pelican" if you want to focus on the posts from this forum.

[tommott]

Originally Posted by MichaelSJackson

Google "993SS 3.2SS" and you'll find a lot of owners happy with the Dougherty cams in your configuration.

Or Google "993SS 3.2SS Pelican" if you want to focus on the posts from this forum.

Thanks for that. Somehow I had 993 stage 2 cams in my notes but they're actually 993 super sprint cams. Now that I am looking up the correct thing I got all the good info including a dyno chart I was looking for.

3.2 SS: finally got it on a dyno

Looks like they're about as aggressive as you can go with CIS pistons and torque starts coming on around 4500 rpms to redline.

[David Inc.]

One thing I've wondered about with new cams and new EFI is how do you do cam run-in? I've always understood that the cams have to be broken in by running the engine at a slightly higher rpm right from the get-go, so what happens if the engine isn't running right and you can't get to the necessary rpm?

[jpnovak]

Originally Posted by David Inc.

One thing I've wondered about with new cams and new EFI is how do you do cam run-in? I've always understood that the cams have to be broken in by running the engine at a slightly higher rpm right from the get-go, so what happens if the engine isn't running right and you can't get to the necessary rpm?

You get the car started and it may be running less than optimal mixture. Then you raise the rpm so that your breakin process has lots of oil flow and sufficient pressure to flush assembly lube and do your mechanical run-in. During this 20 or so minutes you are tuning on the laptop to refine the mixture. It only takes a few seconds to adjust the mixture. Pretty much a drop in the time bucket compared to the length of time for break-in.

[macssc911]

Not sure on CIS pistons, I run 98 P&C JE 10.5 ,went with Elgin S grind cams with PMO 46s, so just driving around very civilized smooth driver. However if you get an itchy right foot the cams and the carbs marry up around 4K and pull is scary to 7K. Basically it’s a Jeckel and Hyde. I would think with CIS pistons you could go pretty aggressive with cams and still have plenty of clearance.

[jpnovak]

AFIK, there were no 98mm CIS domed pistons. At least not factory ones. There were several versions of a "wedge" style piston which was asymmetric favoring a squish zone on the spark plug side of the head. For example, the 98mm Max Moritz PC set. These 98mm pistons often had valve pockets machined to provide more clearance with high-lift, high duration (AKA Fun!) cam profiles.

Do you have any documentation on what pistons were actually used? A borescope photo of the piston from the spark plug hole at BDC location would also give you an idea what cams could be installed.

Also, Al builds a great kit. It will certainly run better than CIS.

[onboost]

Originally Posted by jpnovak

AFIK, there were no 98mm CIS domed pistons. At least not factory ones. There were several versions of a "wedge" style piston which was asymmetric favoring a squish zone on the spark plug side of the head. For example, the 98mm Max Moritz PC set.

jpnovak is correct... just happen to have some of those sitting around. Both sets are
98mm Mahle Max Moritz.

[tommott]

Originally Posted by jpnovak

AFIK, there were no 98mm CIS domed pistons. At least not factory ones. There were several versions of a "wedge" style piston which was asymmetric favoring a squish zone on the spark plug side of the head. For example, the 98mm Max Moritz PC set. These 98mm pistons often had valve pockets machined to provide more clearance with high-lift, high duration (AKA Fun!) cam profiles.

Do you have any documentation on what pistons were actually used? A borescope photo of the piston from the spark plug hole at BDC location would also give you an idea what cams could be installed.

Also, Al builds a great kit. It will certainly run better than CIS.

The only documentation I have is the hand written receipt from the shop that originally built the motor when the pistons and cylinders were first installed in 1987! I guess I could be incorrect but I have always been under the impression that the early wedge shaped 98mm Max Moritz pistons would only clear CIS piston friendly cams?

Hopefully I'll have a borescope pic of the cylinders soon.

[Dan J]

I had a 3.2 ss with 46 webers, Max Moritz pistons and Elgin Mod S cams the valves cleared the pistons with room to spare ( you obviously would have to verify on your motor) it was a great motor

[faapgar]

If you want to use 993RS Cams with Max Moritz you need to make the intake valve pockets 0.60 thousandths deeper.At 4.4 lift at overlap intake valve hits the piston.CiaoFred

[faapgar]

Sorry.When I set cam timing I always check an overrev situation.So I turn the valve adjustment screw 4 half turns then rotate the engine.If nothing touches then life is good.That is 2mm of clearance.With the 993RS cams that is 3mm on the exhaust side.That is plenty of room.Ciao FRED

[onboost]

Originally Posted by MichaelSJackson

Google "993SS 3.2SS" and you'll find a lot of owners happy with the Dougherty cams in your configuration.

Or Google "993SS 3.2SS Pelican" if you want to focus on the posts from this forum.

Originally Posted by faapgar

If you want to use 993RS Cams with Max Moritz you need to make the intake valve pockets 0.60 thousandths deeper.At 4.4 lift at overlap intake valve hits the piston.CiaoFred

Originally Posted by faapgar

With the 993RS cams that is 3mm on the exhaust side.That is plenty of room.Ciao FRED

As a side bar.. - Fred, I get what you're saying with regard to needing the additional clearance in the pocket... but are you saying that the Dougherty 993SS cam is the same spec/profile as 993RS Cams?

Thx

[Nux]

If it is original Max Moritz kit - which is likely if i was done in 1987 - you have 9.3 compression. That and the wedge shaped domes limits your cam choices.

I had the excact same combo in my '78 targa and checked the compression: spot on 9.3.

I used DC20's which is similar to 993SS and car is dynoed at crank 243HP with Thriumph ITBs.

However, to day I would consult William Knight about his Melissa cam or maybe go CatCams. Both seem better in any way.

[tommott]

Originally Posted by Nux

If it is original Max Moritz kit - which is likely if i was done in 1987 - you have 9.3 compression. That and the wedge shaped domes limits your cam choices.

I had the excact same combo in my '78 targa and checked the compression: spot on 9.3.

I used DC20's which is similar to 993SS and car is dynoed at crank 243HP with Thriumph ITBs.

However, to day I would consult William Knight about his Melissa cam or maybe go CatCams. Both seem better in any way.

Thanks for that. Those were my same assumptions; original Max Moritz pistons due to date they were purchased and installed to go along with the original Max Moritz piston cam limitations. Hope to get the pics of the piston domes today. There’s also some handwritten potential part and/or serial numbers under the pistons on the shop’s old school handwritten invoice. I Haven’t had any luck googling those numbers, maybe I can try calling Mahle if worst comes to worst. I’ll post the invoice below in case anybody recognizes those numbers.

Do you happen to have a dyno with the DC20 cams? Cant say I’m entirely pleased with the one dyno chart of a 3.2SS with 993ss cams I saw (linked to above). Awesome power but the torque comes on pretty late. From the charts I’ve seen the GE40 looks to have the best torque curve for the 3.2ss but I believe those supposedly won’t clear the original MM pistons. From what I’ve seen and am aware of that works with the MM pistons at this point, the 964 cans seems to have the best looking torque curve.

[Nux]

The DC20's had to be timed at 1.8@1mm to clear the exhaust valves - not optimal on a low comp engine. So the torque curve is not perfect. Top end is ok.

Again, I would not go this route today. I got the DC's dirt cheap at the time (years ago), so thought I would give it a try. Thats not the correct way to build a good motor.........

To accommodate your new ITBs, I would install new pistons with higher compression and then go for Williams "Melissa" cam.

[tommott]

Originally Posted by onboost

jpnovak is correct... just happen to have some of those sitting around. Both sets are
98mm Mahle Max Moritz.

Thanks for all the help guys. Sorry for the delay in getting back. My buddy did his best with the inspection camera and taking some pics. Hard to make out with 100% certainty with all the carbon build up but it appears that the pistons in the car are mostly flat faced with smaller valve reliefs. Looks like there is a small wedge like the first set of pistons that jpnovak posted. Definitely not a wedge to the extent of the second that jpnovak posted though.

I was not aware that there were different versions of the max moritz 98mm pistons. Am I correct in assuming that I should be running CIS style cams with either version of the MM 98mm pistons?

[tommott]

Here are the from the inspection camera pics

[targa72e]

One of the things you might consider is measuring how much clearance you have with stock cams. Since the adjuster screw is 1.0 pitch each turn is 1mm. You can turn the adjuster in 1/2 turn at a time and rotate the engine by hand with spark plugs removed. When you run out of clearance you will not be able to rotate engine. Knowing the clearance you have with stock SC cams should allow those providing cams to tell you what could work with the pistons you have.

john

[Jeff Alton]

Check out a dyno sheet we posted in the Engine Building Forum of a similar build, twin plug. We ran 10.5:1 CR as we had twin plug. It has the cam choice shown.

We are also building a 3.2 SS with 46PMO carbs right now where John had a very different cam choice due to the 9.5:1 CR.

Contact John at DRCamashafts to get some advice as well.

Cheers