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martin_gibson 08-22-2005 01:25 PM

Can anyone identify the porsche serial numbers for the RS3.8 barrels, conrods and pistons and list what additional parts and/or modifications would be required to upgrade a 96 993 (nvr intake) from 3.6 to 3.8l.


Martin Gibson
83SC 3.6

Bill Verburg 08-23-2005 05:33 AM

Start w/ the crankcase, spiggot holes need to be bored from stock 107mm to 109mm and a groove for the profile rings needs to be machined into them. 110.72x3.53mm profile ring seals will be installed there.

p/c are 993 103 915 42(43,45,46,47,48) depending on weight class

conrods are stock 993 there are h/d versions available

the heads have larger ports, you neeed too port a stock 993 head

intake valves are larger, Na cooled on both I/O, 51.5/43.5 mm note the exhaust valve is the same size as a stock v-ram but has Na cooled stems


some other relatively minor harware and accessory things are also different but not that important.

the lower v-ram intake tract is larger as are the injection blocks

martin_gibson 08-23-2005 10:07 AM


Thanks for your response.

I can source a set of (hopefully legitimate) 3.8RS pistons, conrods and barrels with the following casting stamps - pistons (mahle 102PG), conrods (993 122.2R' and '993 121.5R' on each side) and barrels (no apparent markings) plus a claimed mileage of 12000 miles.

Before I consider making an offer for these components (which I may tuck away for a rainy day), I really need to get to grips with the total cost of the 3.8 upgrade, so any insight you may have regarding a recommended source and/or cost of the additional components you have identified would be much appreciated.

Finally I would be very interested to know your views on whether this upgrade is actually worthwhile?

Appreciate your help.

Best regards

Martin Gibson
83 911SC 3.6

Bill Verburg 08-23-2005 10:59 AM

Don't know about the casting #s
this is what mine looked like

3.8RS piston on left is grafel coated, has tapered wrist pin

Here's a cylinder

martin_gibson 08-23-2005 12:20 PM

Hi Bill,

Your photographs definately match the parts I have seen so this is a very good start.

The next hurdle is to undertake a cost-value exercise to source the balance of the parts and impliment the 3.8RS upgrade.



83 SC 3.6

Cookie Porsche 08-23-2005 11:27 PM


Not as thorough as Bill, but I agree.

With all the parts you can 'get', rather source a new 964 core and build a new 3.8 from scratch - silly to strip a good engine to add 200cc with all the parts you have.

But IF you have to. Don't just fit a 3.8RS cam, go one better and get a Supercup or RSR cam or similar.... There's so much more power to have and the car will still be as docile as a lamb.


martin_gibson 08-24-2005 11:25 AM


Thanks for your advice.

Other than cost is there any particular reason why you would recommend a 964 core rather than a 993 core as a basis for a 3.8 upgrade?


83 SC 3.6

Cookie Porsche 08-24-2005 09:12 PM

964 and 993 bottoms are the same thing, same oil pump etc (if memory serves me right...).

My thinking was that your current 3.6 is worth plenty $ ( ?). If you strip parts of it the parts will be worth little money. Rather build a second engine with all the parts you can source - that way your car will also remain mobile while you build the new 'monster'.

Most Porsche Nuts would love to have a spare 3.6/3.8 hanging in the garage! Best investment around (that's what I tell the wife at least...).


Bill Verburg 08-25-2005 04:50 AM

the case & oil pump are the same but.....

crank, rods, p/c, heads are different and mostly non interchangeable

i.e. you cannot use 993 rods on a 964 crank, you cannot use 993 pistons on 964 rods etc.

martin_gibson 08-25-2005 10:33 AM

Agreed, procuring a second (probably 993) engine definately makes a great deal of sense, leaving the conversion to be done at a sensible pace once I have accrued the necessary parts and funds.

Is your 3.8 a 964/993 conversion or an original RS engine? Assuming the former would you be able to provide me with some rough cost data for the conversion and I would really value your opinion as to whether the upgrade was a worthwhile exercise.

Thx guys.

Martin Gibson

83 SC 3.6

Bill Verburg 08-25-2005 11:23 AM

I started w/ an M64/21 ROW vram, tore it down to the crank and rebuilt w/ all RS pieces, I got a fabulous deal on most of the parts w/ made it affordable, the only thing missing is the mg. lower manifolds and injector blocks(Steve Timmins beat me to them and he is using them in his car)

There are some non Porsche pieces like Raceware rod bolts, custom chip, Webcam RS hyd. cams

The cylinder spiggots needed machining

cyl heads needed welding for strength

backdated 964 cam drives were needed, stronger competition chains, US phosphoous-bronze valve guides,

rotating assembly was balanced, easy to do given the light wt. of the recipricating components, &#177 0.5g

Not counting the base engine the tab was ~$9k parts and labor

martin_gibson 08-25-2005 12:54 PM


What sort of horsepower/torque did you end up with and would you recommend the 3.8 conversion as a worthwhile upgrade?

Thx again.


83 SC 3.6

Bill Verburg 08-26-2005 04:10 AM

3.8 is in the low 300s, The only reason I did it was the screaming deal I got on the parts, list on the p/c was ~$6k US., very satisfied w/ the result.

I also have a '95 993 w/ the RS treatment but w/o the 102mm p/c, just cams, ports, no vram custom chip. That came in at just under 300.

If you need p/c any way and can get a decent price(I saw a set of 102 Mahles for ~$3.5k US recently, they were a step or 2 down from the ones I used though) do other wise it's expensive hp.

martin_gibson 08-26-2005 10:06 AM


Two 3.8's - you're a lucky guy.

Thanks again for your advice.


83 SC 3.6

Cookie Porsche 08-26-2005 09:03 PM


The 3.8 really is a gem with the right cams - good power and broad tourque band. You can also make power with the 3.6, but if you can get the parts... go 3.8.

I do however not agree with Bill's way of measuring cylinder bores! Using plastic Coke cans is a bit inaccurate! (he he)....

Regards, Tom

Bill Verburg 08-27-2005 05:45 AM


Two 3.8's - you're a lucky guy.
1 3.8RS spec in a '76 Carrera chassis
1 3.6RS cammed, non vram in a '95 993

both have roughly the same l/w flywheels, weight of both is similar, gearing is quite different but similar in selected gears.

hp isn't everything the torque of the 3.8 vram is always there, the 3.6 needs to be rowed a bit harder.

weight of both is similar gearing is quite different.

martin_gibson 08-27-2005 11:19 AM


I don't know how I'm going to explain these to my wife when they arrive next week - maybe I should use Bill's old trick and suggest they are 'diet coke' bottle holders?

So all I need now is the other bits?



83 911 3.6

Bill Verburg 08-27-2005 12:39 PM

Ain't no replacement for diplacement , right?

I make it 6 liters of 'flat' six power, w/ nitrous injection to boot

Hope you project goes well, looks like you have a great start. Don't skimp on the other things. It is expensive but you will love it.;)

Tinker 08-27-2005 05:37 PM


What cams did you use in the 3.6RS? Do you have a favorite or a recommendation for the 3.6 motor?


martin_gibson 08-28-2005 10:48 AM

3.8RS Upgrade

Sorry I hope you don't mind but here's yet another question?

Are factory 3.8 liter RSR cylinder heads (see photo) compatible with the 3.8RS piston/cyinder set and if so how do they differ from the factory RS heads?



83 SC 3.6

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