t0mbo

Hello friends! As some of you know I have an '86 951 with a LR Super 61 TBB turbo with the #8 turbine housing, pre LR Rogue M-Tune, LR stage 2 intercooler, dual port wastegate, MBC, upgraded fuel system, upgraded headgasket, 3" header back exhaust, spec clutch, factory LSD, koni yellows, 250lb springs, Hawk HPS pads and 17" wheels and tires. In general it has all the normal go fast bits working pretty well together, and I would estimate I'm putting down around 370-380rwhp at 21psi (I would like to think I'm making more, and it feels like more, but that's probably daydreaming).
I'm totally in love with the boost and sound, and the power level feels fantastic and the car makes more power than I know what to do with, however, I am not loving the off boost power at all. The car is a total dog around town, but once boost kicks in the car is a total riot. I don't struggle to put the power down, stop, or turn and the car is generally fantastic when boost kicks in. I'm hitting 1 bar of boost around 3000 rpm in 4th gear, so the turbo is pretty similar to the stock K26/6 in it's spool characteristics... but I really want the car to be better at low speeds. I live at 6500 ft and take it on mountain runs up to 8000-9000 ft which may be contributing to my off boost woes. I've driven other well sorted stock 951s and they feel pretty similar off boost. I've been contemplating options and I feel like there's so much collective wisdom on these boards that I should ask the gurus who have come before me for their opinions. I am just asking for opinions, so don't be offended if I don't necessarily follow your prescribed path I should mention that the car is 100% street driven and is mostly used for weekend canyon runs, or times when I want something a little more special to drive. It is not my daily and never sees a track. I'm not really interested in an LS swap at this time. Okay! On to my current possible options (at least the one's I've considered so far) -

Option 1 - Take the car to a dyno tuner and see if a good tune can help with my off boost power? I'm wondering how much can be gained with the current Rogue M-Tune setup, or if I'm just asking too much of a stock 2.5 low CR motor at high altitude. This would involve finding someone in the Colorado region who can dyno tune the Rogue setup.

Option 2 - VEMS. I've been looking at this and it looks amazing and would give me the added benefit of being a great incremental step towards option 3, if I can't get enough low end grunt with just engine management. Everything I've read seems to indicate that I would see a nice bump at low RPMs, plus a lot of other benefits for possible future mods. This would also involve finding a dyno tuner in the region who knows VEMS.

Option 3 - 3.1l hybrid stroker. This looks like the best option, but is pretty extreme for a guy who is happy with 400ish hp on a street driven car. The plan would be to get a donor bottom end to build and pretty much follow Shawn's exact 3.1l build then do a motor swap so that the car wasn't down while I'm building the motor. My brother in law runs a European performance shop and is pretty familiar with 951s having owned and modified a few of them, so we would build the motor together. I would love to get the experience building/helping build a motor under the watchful eye of someone who knows what they are doing to hopefully keep me from doing something stupid. I think a big 3.1l with the TBB Super 61 and VEMS running 1 bar of boost would be really sweet and give very nice power curve and probably get me near 400rwhp which is plenty for me. Obviously this is kinda pricy and maybe too extreme?

What other options am I missing? Should I be looking at gears? Should I just get used to the power delivery and enjoy it for what it is? I always have a tendency of wanting to build the next thing, and maybe I just need to learn to love the car with its charming vintage turbo lag. Changing my thinking is definitely the cheapest option

V2Rocket

Swap in an S2 transmission which has a shorter axle ratio (3.875 vs 3.375 stock)

951and944S

Do you still have the stock 16" wheels...?

I just stripped a few transmissions for the cases and to sort/save the good internals.

Have a good S2 R & P.

T

gpr8er

3L. Totally transforms the car. The 2.5 is no comparison. The 3L performs like a V8. Off boost is now not an issue.

t0mbo

This is fascinating! I swapped the diff on my e34 535iM from a 3.46 to a 3.91 and it completely transformed that car. The only thing I don't like is the high revs at highway speeds, but apparently in the case of the 951, swapping the S2 5th gear and final drive gives shorter 1-4 and still keeps a nice highway RPM. I totally did a google search blitz to find everything I could on this after your suggestion and came to the hasty conclusion that I would love to find the R&P and 5th gear if possible since I already have a LSD in my car, but of course a whole LSD equipped S2 gearbox would be great if I could find one for a good price.

This is fantastic! I'm absolutely interested if you want to PM me. This is precisely the reason this forum is so useful. I don't suppose you would also have the 5th gear from that gearbox would you? I am currently running 17" wheels with 255/40R17 and 205/50R17, but I'm wanting to go with a square 255 setup if I can ever find a set of the MY03 Boxster S II rear wheels to put on my front. So far I haven't found anyone selling just the rears for a good price (granted I have barely put the effort into looking since I rarely push my car hard enough to understeer).

gpr8er

same as a downshift. The torque of a 3L is no comparsion.

Chapman951

What about :

VW/Audi 07K (2.5L 20V I5) Swap Thread

https://rennlist.com/forums/944-turb...ap-thread.html


Car looks beautiful. Love the stance.

fejjj

I did Shawn and Sid’s 2.85 Hybrid stroker build with similar mods as you and the low and mid range power is much better.

I also added the 4 degree cam advance key.

t0mbo

Thanks for the input! What route did you go to get to 3.0L?

Thank you or the suggestion! I have been watching the 07k swap thread and videos very closely. It's a really great concept and I think it might be right for a future build, but at this time I think I would prefer to keep the stock Porsche 4 since I'm 95% happy with the motor and it's well sorted and maintained. I would love to see some 07k swaps finished and driving so I can get an idea of possible hiccups and reliability before making a judgment for my own car. I love what those guys are doing though. Super cool!

Cool! I looked at this as well, but it seems that once you're building a motor the cost of finding a 3.0l crank to use to build a 3.1l is a negligible difference. What are your thoughts? Do you feel that the 2.85l is plenty of low end grunt and you don't need any more? Also, does the 4 degree cam advance help with off boost power?

Chris White

The simple answer (and its free too!) is to change your driving style and never drive the car under 3k rpm. You get used to it after a while and it becomes your normal driving style.
3.0 is helpful but still will not make a huge difference below 3k rpm - in fact off boost its a linear comparison - 20% more displacement = 20% more power.....and that is not a big difference off boost!
Going to a small turbo will help but then you will start to lose top end. For street cars and many track cars I do not go with 'big' turbos - torque coming out of corners is way more important than big numbers at 6500 on a dyno.

fejjj

Chris is spot on as always!

After rereading your post, I realized that you are talking more about off boost.

There is not a whole lot you can do there.

You can however get a better turbo that spools up better and keep your rpm higher as stated.

GPA951s

I Just breezed through this thread but I have to ask... Are you still using the stock Cycling Valve? ( If you are) I had the same issue on my street car and put a "Boost Enhancer" on it... Basically it makes boost Lower (Before the CV actuates) and it feels WAAAY Better down low... Might wanna try it... AS a test you could pinch the WG hose shut and drive it around to essentially feel what it would be like .. Needle nose vice grips work well... Be careful …

MAGK944

What you need sir is a supercharger. Test drive a twin-charged Volvo T6 if you think I’m joking.

lart951

you guys are noobs, check this out 750hp @ 1.3bar how about that?

CyCloNe!

supercharger for low end and turbo for top... twin charge that baby lol, jk. Best cases have been mentioned larger displacement, swap S2 trans, engine swap audi or chevy, smaller turbo for better low end response and sacrifice the top end. I remember back in the day someone was working with a diesel turbo and got it to spin in the 2k range and still would generate around 400hp can't remember which they used but it was using the VGT or something. This was when Rogue was on the scene and that one dude that would make custom exhaust and intake parts in Colorado with the widebody silver 951 (4-5yrs ago).