3.2SS twin plug build
 

Gents,

I'm about to take on my 3rd engine build. I've recently rebuilt a stock 3.2 and a 3.2ss with EFI / ITB (top end only). The 3.2 was smooth sailing (no changes, just standard stuff), the 3.2ss a little more challenging, but manageable with your help.

I have another '81 Euro spec 204hp 3 liter. I'm planning a complete rebuild, and would like to hear your expert opinions and thoughts. This is not going to be a race engine. Must be streetable. I do not mind a little cammy high idle, but should be able to manage morning traffic as well as trackdays.

General aim: A hot, rev happy engine for the street - hopefully close to 300hp. No forced induction. Old school cool looks and intoxicating engine sounds please. :D And no, I'm not doing a 3.6 swap either.

Cylinders: Carrera, 98mm bore and re-plated
Pistons: Wössner 10.5: 1 or JE 11.5: 1.
Heads: Rebuilt, Twin plug stock small port
Cam: DC35 or DC43 for EFI (I've dropped John a mail)
Oil pump: Turbo
Rods: Standard
Induction: Megasquirt MS2 running dual wasted spark with PMO ITB (Al Kosmal is on the case).
Exhaust: 42mm headers into M & K dual out.
Fuel: pump gas 93

There are many variables here - I know. First, I believe 11.5: 1 on pump gas is ok with dual plug ITB / EFI and the right cam. Do you agree?

The cams suggested above are based on a lot of reading here and there. I've been wrong before though .... Would a longer duration cam like DC40 be more appropriate (Lobe is 102)? Or GE80? Or a more friendly 993SS?

Should I keep the heads small-port or drill them out to say 38mm? Should I use race springs or will the standard be ok?

Will the standard rods be ok?

Thanks!

If you're trying to reach about 300bhp at the flywheel, it will need to make power with some revs. Stock small ports will not do it, definitely have ported to at least 39mm-40mm, or locate some earlier heads with larger ports.

With larger ports, I would stick with JE shelf stock pistons at 10.5:1. Depending on valve clearance and head CC, you will likely be a bit above that ratio anyway as a set of those heads will likely have been shaved down at least once and JE designs the dome from stock CC volume.

Definitely use better valve springs, and my recommendation is a DC65 cam. I built a twin plug 2.8LS with one and I liked it so much I'm using one for my personal engine now (see my thread :D). Peak power with the 2.8 was around 7500rpm, so in a 3.2ss it will likely be around the same.

Oil pump, turbo or even 964 will do fine and is much less $$.

Lighter rods is an added bonus. Carrillo rods are some 200g lighter and that indeed makes a difference when you multiply that weight x 6, then multiply further by 7000rpms. That's a lot.

Good luck!

I think that the 11.5-1 compression ratio is acceptable, as long as the driver is careful and does not try to pull the throttle wide open at lower engine speeds, with the DC65 cams and bigger ports. It will also require careful tuning, with lots of attention paid to the ignition curve. Weather in Copenhagen is a lot better (cooler) overall than in Atlanta.
Just my 2 cents.

Good idea on the 964 oil pump! And I'll look into the DC65. They have a LC of 102. Don't you have idle problems? Nice Engine by the way! Any dyno numbers yet?

I can cc the heads before choosing pistons. I could also have the shop shave just a little bit of the pistons if I'm too high. And yeah - the weather over here is usually quite cool.

I have a friend who's currently running a 3.0 converted to EFI, with CIS plenum, 993ss cams and 10.5:1 CR - single plugged!! So far no issues. But then again, the engine is not even broken in yet. Should be interesting.

The DC65 cammed engine is in a twin plug MFI rig, runs great. The DC65 cam ramp speed is a bit more aggressive than a DC60, and has a touch more lift, but otherwise the intake valve closes just a degree or two later than a DC60 so I would think they would have very similar characteristics, but the additional lift of a DC65 is good IF your heads flow.

My engine isn't running just yet, but it's mounted and wired up. Just have to get the time to finish off the AEM base map and calibrate the crank and cam sensors. Very busy at work lately!

I completely agree on the port size and valve spring upgrade. I would also suggest installing a 50.5 mm intake valve. With doing that, you get the benefit of being able to actually put a good valve seat profile with some angles to increase the flow dramatically. That size valve will utilize the factory valve seat as well. Combined with the port work and John's camshafts.... it will be a nice economical package

What port size do you recommend for a high performance 3.0 and/or 3.2SS?

Also, my machine shop talked about porting the exhaust side whereby they could create a venturi effect. Mostly done on turbo engines apparently. Do you also recommend this mod?

The heads are completely stock now and engine never opened. So I guess 90CC as usual (will measure of course). JE has 11.5 shelf pistons, so is there any reason not to use those if I choose a cam calculated for dynamic CR around 8 or 8.5 (if possible)?

The first thing to understand here is that dynamic compression is nearly useless. Effective compression is what makes sense. As the motor spins, the engine is more or less efficient at one rpm vs another due to the head flow and rpm. Peak torque is always realized at about peak volumetric efficiency. Cam selection is extremely important obviously. With DC60 cams and 39-40mm head ports on individual throttle bodies, your engine will undoubtedly be flowing at greater than 100% volumetric efficiency at peak torque, meaning the static compression ratio of whatever pistons and heads you end up with (~10.5:1 or ~11.5:1 as you quoted) will be exceeded if flowing at greater than 100% volumetric efficiency. As an example, at idle the engine may have 75% volumetric efficiency. My point is that it fluctuates and static compression is always eventually realized if, and only if, the air flows well. This is how the previous generation naturally aspirated F1 engines made so much power, they spun the engines to 18k rpm and greatly exceeded their static compression. This is also how some can run 10:1 on single plug ignition, their heads may simply not flow enough to reach even 100% volumetric efficiency meaning 10:1 compression is at no point realized. With current gasoline, I don't care what country it's in, it's not all that great, so if you're looking to move a bunch of air and spin the engine high, 10.5:1 would be plenty IMO as it's likely going to get near 11:1 at peak VE which is really pushing things.

That makes perfectly sense.

Right now I'm a little torn between staying 3.0 or bump to 3.2SS. I have carrera Kolbenschmidt cylinders available and could bore and re-plate those to go 3.2SS.

95mm or 98 mm pistons costs the same. The bore and re-plate is about 1400$. Seems like the obvious thing to do right?

Yeah same cost, why not right?

I would port the intake 40mm / exhaust 39mm
I also stock a complete lightweight 8mm valvetrain package for your application if you are interested

If I could add something here too.

Your first two decisions to be made are, what are your performance expectations and what is your budget.

Do not guess anything here. There are too many opinions that are based on "their" engine and not yours. You cannot choose a cam without first knowing the air flow through the intake system and head. The other engine parameters are very important as well.

Once you have figured out the performance you want, the basic engine parameters can be set and the airflow required can then be calculated. Then you decide upon the port size and a cam profile that will support the performance level wanted.

There are not many places that can give you the known airflow through a given port size. Bill is one that can, so I suggest you consider using his knowledge to obtain this critical information.

Once this all known, choose a cam carefully based on what your engine needs not on what others think you need. And, don't over spring the valve train. This is the biggest mistake a lot do. Seat pressures are typically chosen out of fear and not based upon weights and seat widths etc.

I often read where seat pressures of 80-90 lbs are suggested. Either the cam design is horrible and it requires huge forces to dampen the harmonics or fear has taken over.

valve seat pressures
 

Well said Neil.Lack of knowledge breeds fear.Stiffer is ok but coil bind at full lift is a killer.Cam and lifter wear and H.P drag is a dowmside to improper spring pressures.These motors are air pumps and the exhaust system is the most overlooked aspect of DIY builds as your efficiency in scavenging makes your motor breathe.I build my own exhaust headers for the last 40 years as there are few options out there that work.30 H.P waiting below the exhaust port.Fred

Definitely go wilder than ModS (GE40)
Even 80s in a 3.0 are not that wild, idle fine.
Spend money on dyno tuning or do it yourself with good AFR gauges and logging. It can be worth 20% or more!

choose cam according to intended use. For my use a milder cam make more sense and makes for a more efficient & quicker car on the kind of driving I favour. Also a milder cam is more forgiving towards tuning and exhaust/inlet issues . A matter of personal taste and budget

What would be your "seat of the pants" description of the characteristics of these two cams.. from riding in or driving the car using them?

Excellent details Bill.. always that little extra to be had. Thanks to you and Neil both for proving input!

Regards,

First engine was an MFI motor. Idle was good while drivability showed no huge gaps in power like an RSR cam does i.e. nothing nothing nothing then everything at 4500rpm+. Not at all like an RSR cam, DC65 has enough meat in the power band to drive around town just fine, then most of the power comes north of 4k rpm. I would not use one in a carbureted motor as I would think the vacuum signal to the carbs at in-town speeds would not be all that powerful thus resulting in less-than-great drivability.

lvporschepilot, thanks for the reply.. sounds like something I could use.

My build will be similar to Nux, 3.2SS as I am actually kinda cleaning off the shelf with items collected over the years so 98mm p/c, fresh set of flowed twin plug heads, and 40mm TWM ITBs. The only thing missing is a proper set of cams.

Thx

Don't you think 40mm ITB's will be too small for that application?

Good catch and I do think they will be to small. However, I also have a set of 46mm ITB's that are slated for another project. So if I'm lucky, I can run it with these until there are funds available or I can trade for another set of 46's.

I'm still considering staying with 3.0. I have both the original 95mm SC cylinder and also 95mm Carrera cylinders (Kolbenschmidt). My local machine shop guy - who has been working with Porsche engines for a lifetime - does not really like the idea of a 98mm bore and a re-plate of the old Carrera cylinders. He strongly recommends a new complete C/P set which is mucho dineros.

Apparently, he's afraid os heating issues and reliability in stressed situations (track time etc).

What are your thoughts on that?

replate 98mm
 

Use U.S.Chrome for replating.Ciao