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Engine and transmission rebuild - what would you do?
I'm returning to aircooled cars after over a decade with a restomod/backdate project and would appreciate input on how to approach the engine and transmission.
The idea is to use the last of the torsion bar cars to build a fun road car that will be mostly used for canyon runs. I'm specifically looking for a 3.2 with a 915. I want to retain the character of the early cars and ideally end up with a car that is numbers-matching. I want to aim for ~2,200lbs and don't need the biggest displacement. I'm sure everyone here knows that chasing power is an exercise in diminishing returns with aircooleds and I want to stop at that point where returns nosedive. My thoughts are that the 3.2 and 915 retain the character of the older cars, which is what I'm looking for, so the 3.6 VR conversion, as logical as it may seem, would take me away from that feel and would no longer be a numbers matching car (this is secondary, but nice to have). What I mean by that is I'd like that progressive build up to 3k that bursts at 5k matted to a shortish ratio box that is light, easy/cheap to work on, and has that early car character.
All of this said, here's the plan for the 86 euro spec I have a deposit on: shorten gears by swapping 2nd, 3rd, and 4th for 3.0 SC gears, bore out to 3.4 or 3.5, 964 cams, and twin plug.
Here's where I need help: retain EFI with ITBs and a custom chip or go with carbs? I don't care very much about fuel economy and carbs seem to add both power and character to the engine. My only concern is service and reliability as I haven't had a carb car in a long time and frankly can't recall what it's like to live with one.
The best of the 915 cars is the 86. Stripping an 86 down to 2200 lbs will be quite an exercise. IIRC my 71 is 22xx. Maybe almost 2300 now with the engine build on it.
If you are willing to spend the $ for tuning and sorting, EFI is 100% the way to go. You can see what I did on my 2.8, but plan for 3x the price for induction with EFI vs Carbs. A set of PMO and all the bits is what 7k? Carbs SUCK, but carbs are 'easy' but optimization is an art, and they never stay consistent. And if you go to altitude the tune changes. I'm very happy with my ITB setup and motec. Cold start, hot start, idle, sea level, 7k ft, the car just runs fantastic, always. Mine is EFI, dual plug, coil on plug, dual knock, all the modern sensors plus idle control. In full power, carbs and EFI will be similar, but it's the drivability where EFI is just drastically surperior.
Do keep in mind the 3.2 cars have a good system with motronic, but if you do a 3.4 (most common) you may go beyond what the stock induction can handle.As to what to do on a 3.4 for a build, just find your engine builder and spec your objectives.
Regarding the trans, there are a few in the US (assuming you are in US) that build these all day long. Plan about 1500 give or take for the labor to build + all parts/shipping. Bill Rader built my 71 911/01 transmission. BBI built my engine and did all the engine controls and tuning.
@Spyerx thank you very much for that. The car will be completely stripped down and rebuilt from the ground up. It will be a new car when done with a corresponding budget. Because of the scope, I am expecting to reach my weight goal. It's a big priority. Questions:
Can you elaborate on what makes the last of the 915s the best one? The 915 from the SC has shorter gears and that's something I'm looking for but I'm not an expert.
Your comments about consistency and correspondingly, maintenance is what concerns me about going with carbs. My mechanic is steering me in that direction to add character and power for a reasonable cost. Can you give me a sense of what I'd have to spend to add EFI ITBs and aftermarket ECU? I'm hoping to end up with a free and high revving engine and that's another reason for the carb suggestion. Will EFI with mods match the power, responsiveness, and higher redline of a carb system?
Is 3.4/3.5 worth it or should I simply optimize the 3.2?
The car will be built in Germany using various longstanding and respected specialists. The current budget is around $30k including taxes just for the refresh of both the engine and box.
When I say best, the 86 was the last of the 3.2 915 cars before 87 moving to G50. It's regarded as the best of the 3.2 cars. I'm not certain on trans changes.
Gearing, is very specific to your use case and your engine power/curve/driving characteristics. If you are going to go through the effort to rehear the box, I wouldn't just try to match an SC, do it top to bottom to best match the engine to the car.
3.2 vs 3.4? Well, that's simply a budget question. If you want power you build the motor, but you have to have a goal in mind, what is the objective? Revs? only a little more power? Durability? etc. a 3.2 in a 2200 lb car with a short gearbox is going to be super quick.
Prices must be much cheaper in Germany than the US. You'll pay $10k on a regear, labor, and engine build with a change to ITB EFI can easily be 60k US. The induction, ITB, all components, ECU, harness alone will be 15k+, add labor, hard parts on the engine... I'd check with some builders and ensure your budget is in line with reality to do what you want.
When I say best, the 86 was the last of the 3.2 915 cars before 87 moving to G50. It's regarded as the best of the 3.2 cars. I'm not certain on trans changes.
Gearing, is very specific to your use case and your engine power/curve/driving characteristics. If you are going to go through the effort to rehear the box, I wouldn't just try to match an SC, do it top to bottom to best match the engine to the car.
Agreed, which is why I'm trying to secure this 86. I don't want the G50 and would suspect that the last of the 915s to be excellent. However, I also know that gearing started getting longer and longer with each evolution and was rather long by the time they got to the 993. I've come across a few references to the 3.0 as it being the sweet spot with the 3.2 being slightly longer. However, you make a good point about matching the box to the engine. Perhaps I need to land that first.
Originally Posted by Spyerx
what is the objective? Revs? only a little more power? Durability? etc. a 3.2 in a 2200 lb car with a short gearbox is going to be super quick.
That's the thing, by focusing on weight and chassis, I don't think I have to worry about displacement to build an enjoyable road car. I do want a car that is reliable and solid. I don't want to be wrenching on it as much as driving it. I'd love a free revving engine with a 7-7500 redline. That, combined with weight savings and a solid chassis is more important to me than displacement. BTW, thank you for your questions because they are helping me clarify my priorities.
Originally Posted by Spyerx
Prices must be much cheaper in Germany than the US. You'll pay $10k on a regear, labor, and engine build with a change to ITB EFI can easily be 60k US. The induction, ITB, all components, ECU, harness alone will be 15k+, add labor, hard parts on the engine... I'd check with some builders and ensure your budget is in line with reality to do what you want.
Prices are in EUR and it's just for a basic rebuild of the 3.2 and 915. Everything else we're discussing would be extra so I think it's in the same ballpark as in the US.
Agreed, which is why I'm trying to secure this 86. I don't want the G50 and would suspect that the last of the 915s to be excellent. However, I also know that gearing started getting longer and longer with each evolution and was rather long by the time they got to the 993. I've come across a few references to the 3.0 as it being the sweet spot with the 3.2 being slightly longer. However, you make a good point about matching the box to the engine. Perhaps I need to land that first.
That's the thing, by focusing on weight and chassis, I don't think I have to worry about displacement to build an enjoyable road car. I do want a car that is reliable and solid. I don't want to be wrenching on it as much as driving it. I'd love a free revving engine with a 7-7500 redline. That, combined with weight savings and a solid chassis is more important to me than displacement. BTW, thank you for your questions because they are helping me clarify my priorities.
Prices are in EUR and it's just for a basic rebuild of the 3.2 and 915. Everything else we're discussing would be extra so I think it's in the same ballpark as in the US.
I have read this thread twice and have a few thoughts. First, I own and race cars both in the USA and in Europe, so I am painfully familiar with USA and European costs. Allowing for dollar to Euro conversion, mechanical labor costs are indeed far lower (about half) in Europe versus in the USA . Still, I suspect your budget is a bit optimistic. Second, I wonder why you care about "numbers-matching"? Those of us who do care about such things want originality and would never look twice a car that is as heavily and irreversibly modified as what you plan. I'd ditch the idea of "numbers-matching" and hot-rod to your heart's content.
Subscribed, thank you! Mine will be an ST tribute with a similar level of restomod.
Originally Posted by raspritz
I have read this thread twice and have a few thoughts. First, I own and race cars both in the USA and in Europe, so I am painfully familiar with USA and European costs. Allowing for dollar to Euro conversion, mechanical labor costs are indeed far lower (about half) in Europe versus in the USA . Still, I suspect your budget is a bit optimistic. Second, I wonder why you care about "numbers-matching"? Those of us who do care about such things want originality and would never look twice a car that is as heavily and irreversibly modified as what you plan. I'd ditch the idea of "numbers-matching" and hot-rod to your heart's content.
Thank you for that feedback. Those are the starting point numbers I was given by the shop but good datapoint to have. As for the numbers matching, like I said, very secondary interest. My primary concern with swapping for a 3.6 is changing the character of the car from classic momentum car to modern torquey car when peak power is not my primary objective.
I'd appreciate your thoughts on cabs vs. EFI in the context of wanting that classic feel but wishing for reliability and consistency. For example, I live at sea level with a lot of humidity and one of the roads I will frequent takes me up to 5k ft within an hour. I don't know what happens to a carb car with those kind of ambient changes which has me leaning toward sticking with EFI.
Part of the reason i bought my 71 is the engine was not original. Less guilt modding it.
I live at sea level and drive up as high as 7k ft. My old carb engine just wheezed and barely idled, it was decent at sea level. The efi setup runs great all around.
another option especially if the engine is in good condition is do all the work and shorten the gear stack. Keep engine as is. Then decide. A 3.2 is a 2200 lb car will be fast. Driven a couple long hoods with stock 3.2 in them.
I'd appreciate your thoughts on cabs vs. EFI in the context of wanting that classic feel but wishing for reliability and consistency. For example, I live at sea level with a lot of humidity and one of the roads I will frequent takes me up to 5k ft within an hour. I don't know what happens to a carb car with those kind of ambient changes which has me leaning toward sticking with EFI.
All five of my vintage cars run carburetors; I have no experience with EFI in a vintage car. I principally live at 1600 meters and the cars are jetted for that altitude. I frequently drive to my second home at 3000 meters, crossing a pass at nearly 4000 meters, all in the period of one hour. There is no problem at all (in fact, the maximum octane pump gas here is 91 octane, because there is no benefit of higher octane at such high altitude for a street engine). I often race at 0 to 300 meters above sea level, and for those races I do jet down. That is not as easy to do on an early 911 (Weber 40IDA or 40 IDF carbs) as it is for some other cars; fortunately, I don't have to do it often.
Your car being jetted for sea level will be OK at 5000 feet; you may feel lower power at the higher altitude, but you won't damage the engine.
Part of the reason i bought my 71 is the engine was not original. Less guilt modding it.
I know that guilt. The car I'm planning to buy is a nice 300k km car with original paint and no rust. Silver with black interior. A really nice car to restore to original spec. I've gotten over it now but I almost passed for that reason.
Originally Posted by Spyerx
another option especially if the engine is in good condition is do all the work and shorten the gear stack. Keep engine as is. Then decide. A 3.2 is a 2200 lb car will be fast. Driven a couple long hoods with stock 3.2 in them.
I am considering a straight forward refresh of both engine and box, adding EFI ITBs with a chip and exhaust and calling it a day. Unfortunately, as I'm sure everyone here knows, the pull to mod is always strong, especially in "while I'm in there" situations like mine.
Originally Posted by raspritz
All four of my vintage cars run carburetors; I have no experience with EFI in a vintage car. I principally live at 1600 meters and the cars are jetted for that altitude. I frequently drive to my second home at 3000 meters, crossing a pass at nearly 4000 meters, all in the period of one hour. There is no problem at all (in fact, the maximum octane pump gas here is 91 octane, because there is no benefit of higher octane at such high altitude for a street engine). I often race at 0 to 300 meters above sea level, and for those races I do jet down. That is not as easy to do on an early 911 (Weber 40IDA or 40 IDF carbs) as it is for some other cars; fortunately, I don't have to do it often.
Your car being jetted for sea level will be OK at 5000 feet; you may feel lower power at the higher altitude, but you won't damage the engine.
Thank you for sharing your experience. Very helpful. Carbs will be a new experience for me and they seem to be polarizing here and on Pelican. People either love them or hate them and much of it seems to come down to how well the owner understands how to they work and how to tune them properly, something that seems to be a dying art. EFI is practical and straight forward and there's an appeal to that. But there's something romantic about carbs and what they bring to the table that is well aligned with my desire to undertake this project to begin with, which is to go back to basics and to enjoy a raw and straight forward mechanical car. The sound and power they generate is not lost on me.
I'm not committing to either quite yet but I'm grateful to you both for sharing your experiences and opinions. Thank you.
The reason the gearing got longer is because the engines increased in torque through the years. When I went from 2.4S to 2.4RS spec, my first impression was that my gears seemed lower. The RS came with longer 4th and 5th than my S. A high torque motor with shortened gearing might be fine for autocross, but could be irritating on the road. If you go that route I would start with my ideal top speed and go down with good splits.
Keeping in mind where the rpm would be at average cruising.
You'll be hard pressed to get to less than 2500lbs
Best Porsche I ever drove was the 3.0 MFI RS, too bad so few were produced.
The reason the gearing got longer is because the engines increased in torque through the years. When I went from 2.4S to 2.4RS spec, my first impression was that my gears seemed lower. The RS came with longer 4th and 5th than my S. A high torque motor with shortened gearing might be fine for autocross, but could be irritating on the road. If you go that route I would start with my ideal top speed and go down with good splits.
Keeping in mind where the rpm would be at average cruising.
You'll be hard pressed to get to less than 2500lbs
Best Porsche I ever drove was the 3.0 MFI RS, too bad so few were produced.
Very good point. Changing not one or two but a few variables has an impact on other things, gearing being one of them.
Speaking of the SCRS, a video of one accelerating literally just popped in my IG account. What an epic sounding car.
Also on weights, take a look at my 964 thread, that was a 3000 lb car brought down to just over 2600 (I kept AC and did put in some sound deadening/carpet, hood is steel, could have gotten to 2500 with a few more compromises)… the orange car weights around 2200-2300 IIRC. It has a glass splitter, minimal sound deadening, light carpet kit, but is essentially fully fitted out.
Getting a later G down to 2200 will require a lot of carbon/glass and compromises :-)
09-07-2023, 05:04 PM
Engine and transmission rebuild - what would you do?
