Engine Revision to 3.8l - is it worth it?
08-28-2019, 10:30 PM
#32
Rennlist Member
I also did the same on my track Miata. On the above dyno I run 11:1 compression with 9psi of supercharged boost on E85. Makes close to 300whp. Since that has a centrifugal supercharger I had to run cams with shorter than factory seat to seat timing (for even more dynamic compression) but MUCH more duration at .050/.100/.200/.300/.400/.500 to help it breath. The aggressive ramps were designed by webcam.
I love the nerdy side of engine builds. I cut my teeth early on and really got a really good handle on engine designing.
Last edited by MarinS4; 08-28-2019 at 11:40 PM.
08-29-2019, 09:08 AM
#33
Rennlist Member
Nice numbers MarineS4. I hope to see about the same or a bit more when I am done and a nice linear graph. I was not pleased with the chip tune that was done as seen in the graph above although on track you're always in the power band. Adding the stand alone smoothed out the curve tremendously brought the engine up to nearly 500 wh/tq but the power dropped off too early. So I am starting over with everything new. What did you do to drop it from 11:3 to 11:1? I will be running a little lower than that and plan to play with the boost more. I will also tune for E85 although until I can find a reliable source for it or the tracks begin to offer it I don't plan to lug a 55 gallon drum with me to the track. My wife also drives and we would burn through the stuff like crazy. Might need 100 gallons for a three day event.
I am assuming you retained the Vram. I decided to ditch mine and will be using GT3 intakes with some custom fabricated parts. Looking forward to the results. There are a lot of advancements made in the past few years. Although I will say there is something to say bout the rush the old school single turbo low compression offers on the street. Although I just tuned my sons '15 Audi A3 with down pipes and the thing is scary fast for a little sedan. It is putting out about 400BHP and very linear.
I am assuming you retained the Vram. I decided to ditch mine and will be using GT3 intakes with some custom fabricated parts. Looking forward to the results. There are a lot of advancements made in the past few years. Although I will say there is something to say bout the rush the old school single turbo low compression offers on the street. Although I just tuned my sons '15 Audi A3 with down pipes and the thing is scary fast for a little sedan. It is putting out about 400BHP and very linear.
08-29-2019, 11:00 AM
#34
I did a 3.8 build with high lift cams recently. Transformed the car. Wasn't cheap, but what is cheap with these cars? For someone intending to keep the car longer term it makes as much sense as a suspension refresh in my opinion as you benefit from having a fresh engine throughout the ownership cycle. If doing an engine rebuild anyway it is not so big a jump to get to 3.8. I'm really pleased with the extra torque, as well as removing all the oil leaks that could only be done on my car by splitting the case and replacing the bolts etc.
For me 3.8 was the maximum I was prepared to go to as Mahle don't make them any bigger, and they are the supplier making them for Porsche. 4.0 would have put me into less well know territory with regard to longevity of the rebuild.
Mine was on 150k when the 3.8 build was done by Tech 9 (Liverpool, UK). It had poor leak down on cylinder 5 before it was stripped and this could be seen on the valves once open. One of the cams had some pitting on it, the cylinders were OK but again bid show some signs of wear.
Full review here:
https://aircooledbug.co.uk/porsche-9...-8-conversion/
For me 3.8 was the maximum I was prepared to go to as Mahle don't make them any bigger, and they are the supplier making them for Porsche. 4.0 would have put me into less well know territory with regard to longevity of the rebuild.
Mine was on 150k when the 3.8 build was done by Tech 9 (Liverpool, UK). It had poor leak down on cylinder 5 before it was stripped and this could be seen on the valves once open. One of the cams had some pitting on it, the cylinders were OK but again bid show some signs of wear.
Full review here:
https://aircooledbug.co.uk/porsche-9...-8-conversion/
08-29-2019, 02:52 PM
#35
Rennlist Member
It's interesting to see the 3.8RS VRAM vs the 3.6NVR. The low end grunt of the 3.8 is night and day. The delta closes as the RPM's increase. I wonder how much of that is Cams. I expected the RS to maintain the torque delta from 5k on, Most everything below that is likely VRAM gains. I suspect more cam would certainly help keep that advantage from 5k to redline.
08-30-2019, 11:29 AM
#36
It's interesting to see the 3.8RS VRAM vs the 3.6NVR. The low end grunt of the 3.8 is night and day. The delta closes as the RPM's increase. I wonder how much of that is Cams. I expected the RS to maintain the torque delta from 5k on, Most everything below that is likely VRAM gains. I suspect more cam would certainly help keep that advantage from 5k to redline.
I believe stock injectors have the following specs
964 195cc/min
993 235cc/min
08-30-2019, 03:12 PM
#37
Rennlist Member
When I see injectors hit the limit on the dyno things go bad fast. I don't think that's what's happening from 5k on. Something is restricting the breathing. That's why the 3.6 to 3.8 delta continues to narrow as RPM's go from 5k to redline. There's good hidden horse power to be had in that 3.8 engine. Could be cheap and easy of it could be expensive and involved. It's worth chasing to understand why IMHO.