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This topic came up over a DM (direct message) conversation on Instagram and I figured I'd go ahead and just open the discussion now for my future planning. Besides, everyone loves a good technical discussion and we're trying to bring back more of it these days, right?
A few things to READ before chiming in to dissuade me from a 3.8L conversion ("not worth it" comments) or the polar opposite (build a 4.0L ...$$$$$).
1) I have a spare set of 993 cases that came with my car
2) These cases are the original cases from the original motor
3) I want them back in the car... at some point
4) My build has been dragging on and at this point, I do not want to rebuild the motor
5) I want to put the existing motor back in (great condition, a few minor top end leaks I'm addressing) and enjoy the car
6) In parallel to #5, I want to begin cobbling together the parts needed for a 3.8L
7) When ready.... (whenever that may be) I will do the conversion (whether it's this coming winter, or the one after that, or 5 winters later... this will be a casual goal)
8) The car will not be a "track" car
That said, I want to essentially go with a euro-spec 3.8L RS setup... aka an X51 retrofit. I may potentially deviate from that with a few extra upgrades (based on input received). I want to keep the Varioram and I'm not planning to go with a GT3 intake conversion.
Looking to start soliciting input on a parts list from those with experience here so I start to build a check-list and gather parts over time.
Pistons? Mahle slip-fit? Which kit number? Is it the PS102-022 slip-fit with 11.4:1 compression ratio? The other slip fit kit I saw (PS102-020 with 9.3:1 compression ratio) looks like it's for Turbo conversions. Since this is a street car, I assume there is no compelling reason to get machine-fit cylinders and have the cases bored out to accommodate the thicker cylinder walls? Looks like Patrick Motorsports typically goes the slip fit route for street cars.
Rods? I believe the Mahle kit I noted above needs different (RSR style) connecting rods? Please confirm. I'm a bit fuzzy on this and can't recall if the factory X51 retrofit kit included new rods?
Heads/valves? What are my options here? Seems there's options and looking for feedback based on people's experiences.
Head studs? Do I need to upgrade?
Cams? Again, seems there's options and RS-spec offerings in the aftermarket (Patrick, etc.)
Based on all of the above and intended use (fun car with a tad of RS-oomph) I presume I don't need to consider a GT2 oil pump? What about titanium valve springs and keepers? Lastly any thoughts on hydraulic vs solid lifters?
Anything else I missed? Again, goal is something very equivalent to an X51/RS-spec. Not looking to spiral down the slippery slope. I'd like to re-gear the trans too but that's a separate topic.
thanks guys...
EDIT: if it was not obvious, I'm asking the community this question because, like all things, I will do all the work myself.
Last edited by boomboomthump; 03-15-2024 at 05:37 PM.
Loving this as when I eventually need to rebuild my engine, I want to do it the same way. A mostly stock X51 with the varioram has been pulling at me.
Thanks for putting this thread together. If it's anything like your other build thread, it'll be a huge benefit to the community. Looking forward to learning....
I won't be one to dissuade you from a 3.8 build. I'm on the other shoulder whispering that you should go the ITB, coil on plug & as much GT3 as possible route.
You obviously know what you are doing and probably intend to do the work yourself, right? If that's the case, I would recommend opening a dialogue with potential 'vendor's' for all of the necessary parts based on their history of successful builds and explain your goals / get their recommendations. You mentioned Patrick MS in your post who have many, many 3.8 builds out in the wild - Rothsport, Dawe or Mirage Intl may be others to speak with.
There are some very knowledgeable members here that also know what they are doing when it comes to increased displacement builds - I'll be interested to read the suggestions.
It's cool that you intend to add this layer to your already very special 993 build.
X51 used slip fit p/c, RS cams, RS single or double alternator pulley, hopefully you have a Motronic 2.1 so a chip can be installed if its Motronic 5 hopefully you have a ''97 that can be reflashed, otherwise might as well plan on a Motec upgrade as well'
If going for Motec might as well go to mechanical rockers and ITB and GT3 intake a lumpier cam but then you need to upgrade the bottom end and oil system, where to stop
It's interesting to note that the above was for retrofits
when building new they added a special damper pulley similar to but not the same as was used on 964
You don't need bigger valves but it's likely that the heads will need to be rebuilt any way so why not, stock,nonvram or vram or RS can be used or even aftermarket SS or Ti versions
anyway i'd start by evaluating the engine control system as that is a major choke point
the slippery slop increases pitch the deeper you go.
Originally Posted by Bill Verburg
... so why not...
most will do this just once - X51 is a solid step, not a lot of additional HP/TQ to be gained from 3.8 to 3.9 to 4.0 NA, but the 4.0 has become a benchmark thanks to PM and GW, and can be reliable, but moves away from OEM 90's tech. It is going on 30 years. In my thinking, for my 4.0 build, the two big inflection / inflation points were GT3 internals and ECU replace, they cost but unlock further possibilities (heads, ITB, cams, exhaust, etc.) to spend $$$s. Without those two steps, X51 "path" is the benchmark for NA in my viewpoint.
the slippery slop increases pitch the deeper you go.
most will do this just once - X51 is a solid step, not a lot of additional HP/TQ to be gained from 3.8 to 3.9 to 4.0 NA, but the 4.0 has become a benchmark thanks to PM and GW, and can be reliable, but moves away from OEM 90's tech. It is going on 30 years. In my thinking, for my 4.0 build, the two big inflection / inflation points were GT3 internals and ECU replace, they cost but unlock further possibilities (heads, ITB, cams, exhaust, etc.) to spend $$$s. Without those two steps, X51 "path" is the benchmark for NA in my viewpoint.
The path you chose is the path for you.
Did you use a damper pulley on yours?
going from 3.8 to 4.0 w/ no other changes is similar to going from 3.6 to 3.8
What really wakes these motors up is cams & rpm, but to use the ones you want you need ITBs, engine management, and 100% GT3 internals,
A buddy has a Rothsport 4.0 there were a lot of other little things done that most of us would never think of including a really trick damper pulley.
Agree....get your current build on the road and soon!
When I did my first 993 non-vram engine rebuild I decided on 3.6 original internals. I used RS hydraulic cams, Steve Wong chip, rebuilt heads with RS size valves and special connecting rod bearings. Cat bypass pipes, RS engine mounts and a short geared transmission w/LWF was an excellent upgrade package and provided 60k miles of use with much track time. Peak +295 hp increase and 270 ft-lb worked well with the short gears and always provided the extra snap when on throttle. Obviously no issues on the street.
Then came rebuild two . Life and funding permitted my moving up to the top step with a Rothsport Racing 4.0L stroker build. Very close to the Gunther Works 4.0L that Rothsport builds. It only uses my original engine case, chain cases, and cam towers. Everything else is new, custom built starting with a Porsche 997 RS 4.0 crank, Mahle p/c, Carrillo rods, ATI balancer, Extreme heads, Elgin cams w/mech lifters, GT3 oil pump, ITBs, GT3 intake, coil on plug, turbo cooling fan, MOTEC M600 ecu, equal length headers and GT3 dual path muffler.
+405 hp and 330 ft-lb with a 7,800 redline on a 2,800 lb 993 that is fully streetable with AC and heat, is hard to compare to my 3.6 RS build!
My mod slope became free fall but resulted in a ride that is always a dream to drive!
My opinion is that on a street used 993; go with 3.8 slip-in p/c, RS valve size, RS cams/hydraulic lifters, stock rods (new bolts), factory ecu chip tune. A short gear transmission and LWF is an excellent way to maximize the available power. As others have said without cams, ITBs, MOTEC and etc, adding the other high performance upgrades will not provide much more usable power.
Bill V. (3.8 vram) and I (w/the 3.6 non vram) have been on track together many times and it is interesting that while the 3.8 is faster at wot, it seems the biggest improvements are in the mid range power delivery.
OK, so who can fill in a few blanks on some of my questions?
@Bill Verburg you asked about engine mgmt. I noted above that I have a '98. It has a GIAC flash on the Motronic via Steve Weiner(RIP). Presume this would simply be another flash and nothing more needed for an X51 type upgrade w/ Varioram.
You obviously know what you are doing and probably intend to do the work yourself, right? If that's the case, I would recommend opening a dialogue with potential 'vendor's' for all of the necessary parts based on their history of successful builds and explain your goals / get their recommendations. You mentioned Patrick MS in your post who have many, many 3.8 builds out in the wild - Rothsport, Dawe or Mirage Intl may be others to speak with.
There are some very knowledgeable members here that also know what they are doing when it comes to increased displacement builds - I'll be interested to read the suggestions.
Yes, as you mentioned, there's knowledgeable folks here who've gone down this path and can at least get me going pretty good in the proper direction. I'm not the type to call up Patrick MS for example and ask them which Mahle piston kit I need, when I know full well I will not purchase it from them (they sell them for $5600 and I can get it elsewhere for $4200, etc).
Certainly if someone says "hey, you should definitely get cams from Patrick MS", I'll certainly call to discuss what I'm doing and what other parts I have on my checklist but figured I'd start my research here on RL vs a cold-call.
Agree....get your current build on the road and soon!
My opinion is that on a street used 993; go with 3.8 slip-in p/c, RS valve size, RS cams/hydraulic lifters, stock rods (new bolts), factory ecu chip tune. A short gear transmission and LWF is an excellent way to maximize the available power. As others have said without cams, ITBs, MOTEC and etc, adding the other high performance upgrades will not provide much more usable power.
Bill V. (3.8 vram) and I (w/the 3.6 non vram) have been on track together many times and it is interesting that while the 3.8 is faster at wot, it seems the biggest improvements are in the mid range power delivery.
Thanks Mike.
Pistons - The 3.8 slip-in P/C kit... these are the 11.4:1 compression ratio, correct? Valves - Any specific recommendation on the valves? (OE vs aftermarket... assuming OE are still available) Cams - I presume the factory RS cams are still available? Or do you mean RS-style aftermarket camshafts (believe Patrick MS makes these, perhaps others) Lifters - OK, hydraulic. Noted. Rods - You said stock but if I have the correct Mahle p/c kit noted above, I saw mention on Patrick MS website that RSR style rods are required?
I have a LWF already. And yes, as mentioned, I'd like to re-gear the trans in order to get the most out of the package. The is part of why I want to stay off the slippery slope with the motor.
OK, so who can fill in a few blanks on some of my questions?
@Bill Verburg you asked about engine mgmt. I noted above that I have a '98. It has a GIAC flash on the Motronic via Steve Weiner(RIP). Presume this would simply be another flash and nothing more needed for an X51 type upgrade w/ Varioram.
Yes a '98 DME can be reflashed, the next question is who can do it, Do they have a stock 993RS compatible or can they do custom.
For the M2.1s Steve Wong is the go to guy, he has both off the shelf for std, RS type builds and custom.
I think that you would likely be happy w/ slip in 102mm p/c stock vram valves and bottom end(though if in there at least beef up the rodbolts), stock headstuds, RS hyd cams are readily available from all the usual cam suppliers.
One other thing as Mike mentioned something like RS or /21 gearing really helps and is something that you would appreciate a lot.
Did someone take over Rennsport from Steve? In my searches this morning on the topic, came across some (almost 20yr old posts) where he mentioned doing the DME flash for these specific X51 conversions.
Pistons - The 3.8 slip-in P/C kit... these are the 11.4:1 compression ratio, correct? Valves - Any specific recommendation on the valves? (OE vs aftermarket... assuming OE are still available) Cams - I presume the factory RS cams are still available? Or do you mean RS-style aftermarket camshafts (believe Patrick MS makes these, perhaps others) Lifters - OK, hydraulic. Noted. Rods - You said stock but if I have the correct Mahle p/c kit noted above, I saw mention on Patrick MS website that RSR style rods are required?
I have a LWF already. And yes, as mentioned, I'd like to re-gear the trans in order to get the most out of the package. The is part of why I want to stay off the slippery slope with the motor.
Not sure on which Mahle 3.8 P/C set to use, as I did not use them. The 11.4 compression ratio is correct for the 993 na engine. With respect to the need for RSR rods, I think the Patrick MS note about needing the RSR rods may be because the 993 rods are narrower than the 964 rods and the kit is for 964 and 993. But this is a guess. I didn't find a note about needing RSR rods on other P/C manufactures.
FVD's kit says: For 964 Models: This set is made to be used with the narrow connecting rod eye of the 993 rods. You can use 993 rods or have your 964 rods machined, but we highly recommend using the Carrillo Rods which are tailored to this application, part # FVD10397503. If you would like to use your 964 connecting rods, send them to us and we will have them modified to the narrow rod eye spec. like the 993.
On my 3.6, Rennsport System (Steve Weiner) did my heads using Porsche RS intake valves and 993 exhaust valve with Titanium retainers and a AASE racing spring kit.
I used Web cams grind number 528/529 which is identified as the 993 Euro RS spec. This is the hydraulic lifter cam.
Building a 993 engine is much different than most engines and I respect your desire to jump into it. Much more like a Harley engine, of which I have build many strokers. On the 993 when modifying cam lift and timing, a lot of valve to piston and valve to valve clearance checking is required. Cam timing is a bit of a challenge as well. But with your technical skills you will enjoy the learning process and mastering it.
Did someone take over Rennsport from Steve? In my searches this morning on the topic, came across some (almost 20yr old posts) where he mentioned doing the DME flash for these specific X51 conversions.
I believe Steve has moved on from Rennsport. Last I talked with him about 3 years ago he was doing some troubleshooting/consulting work.
Agree with Bill V that Steve Wong has some tunes ready for a 3.8/RS build. He includes a second tune adjustment based on dyno run data you send him. And not that you will have the problem but he was the only tuner who could solve the 1995 LWF stalling problem for me.
03-15-2024, 05:33 PM
3.8L RS spec motor build (aka X51 retro-fit)
