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My 2.5SS turbo engine build
I thought I'd share my slow but steady progress of 2.5 short-stroke turbo engine build with you guys both to give some possible ideas for you and perhaps receive some hints on build.
Just to mention that I am very much into diy-er and have been messing with Porsches for around 15 years. I install and tune engine management systems as a "fun job" and work as a quality manager in one of the automotive OEM's and as a journalist in Estonian car magazine. Anyway, here's the build sheet, of which most parts I already have but few have to be obtained: *7R case, shuffle-pinned, with case-savers. I have 4R case right now but will not use it because my friend needs it on his 2.4 build (with 2.2 S pistons, ported heads, S cams, 019 MFI pump, headers etc). *66mm crankshaft *2.2 rods with ARP bolts (modified to fit, need bolts) *T heads from 2.2, ported to 40/37 mm, twin-plugged, full-radius valve seat cut etc. Porting job is almost done, next is twin-plugging and valve guides etc. *RS 90mm pistons and cylinders, these have ~8:1 CR with 66mm crank. *S cams *Twin IHI KHF5-1A ball-bearing turbos (good for around 550-600 hp). *Custom intake manfiold with ITB's and dual-plenum. *Custom intercoolers *VEMS ECU with custom EFI bits. I have all the parts except ARP bolts and suitable case. Even have all the hardware for intake manifold. Regarding triggering, I will probably have to go for custom flywheel (planning to use Tilton 3plate clutch and hydraulic TO bearing, I have the latter on my desk) and I will have the 60-2 patter machined onto flywheel. Here's some photos of the porting job. I used CNC lathe to open up the ports and finished then with burr. Ports still need a finishing done with a sand-paper bit to make surfaces the same between CNC'd and hand machined areas. http://www.porsche-foorum.org/album/...l_911kaas1.jpg http://www.porsche-foorum.org/album/...l_911kaas2.jpg Intake ports. Need to shape the valve guide boss beginning to be smooth. The lines are visible but almost not felt with finger. I will smooth them out still. http://www.porsche-foorum.org/album/...l_intport1.jpg http://www.porsche-foorum.org/album/...l_intport2.jpg http://www.porsche-foorum.org/album/...l_intport3.jpg Exhaust ports. http://www.porsche-foorum.org/album/...l_exhport1.jpg http://www.porsche-foorum.org/album/...l_exhport2.jpg |
Have you considered acquiring an early sand cast aluminum case for this project? Or the case from a '76-77 3.0 Turbo or Euro Carrera? I have had good results with race motors using the early case (some minor modifications useful, but given your machining skills nothing you couldn't easily do). And got one of the later pressure cast cases to use with a 66mm crank on a 2.8SS. I can't see a magnesium case standing up for very long to 400 hp, much less more than that. Unlike the factory racing efforts, most of us need a motor which will run at least 100 hours, if not a lot more.
Are you planning to install special valve seats, or just replace with stock? I once spent way too much time planning a 2.14 liter turbo to fit a race class. Wife vetoed the project, saying we could not afford to learn by breaking. I had to agree, and then class rules changed. I had noted that Porsche used a different alloy in the turbo heads, which led me to think there could be problems with turbo heat using regular heads. I never did resolve that one, though some have made successful turbo race motors using stock alloy heads. The idea of using variable vane/speed turbos appealed to me, though 10 years ago it didn't seem too practical. Now I see Porsche uses this technology. What are you using for your hydraulic TOB? I'd sure like to use one of those when I get my little Tilton installed (2 plate, not as much HP as you are looking for) instead of the cable lever release system I have assembled. But I have gagged at the cost of those which the aftermarket offers for 915s. But am uncertain if I can easily modify one of the standard Tilton or other hydraulic TOBs to mount up on the 915. Especially without your machines and abilities. |
Walt,
I have thought about using early sand-cast case but will not probably do that for several reasons. First being availability and cost. These have to be purchased from US and I haven't seen them for less than $1500+shipping+duties. Second is the fact that this car will be 99% summer street fun car and sees little to no track time. I wouldn't be so pessimistic about 7R case, especially seeing what has been done with it: http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/641141-2-7-turbo.html And that is with no EFI, 1.4 bars of boost and fair amount of abuse. Regarding early turbo case, it would require all other items to be changed as well but I already have a nice set of RS 900 Nikasil cylinders and RS forged pistons, plus all the other 2.2 stuff (rods, crank etc). The RS pistons are lightened BTW. I bought them as a basket case with the car which was previously a rally-cross car and engine was torn apart to fix oil leaks but the owner ran out of funds meanwhile. Valve seats will be stock, I have not decided about the guides. Maybe I'll let my engine machinist who is specialized on head jobs propose some better material and do custom ones. There's nothing wrong with the heads, many cars have pretty soft material, especially after 30+ years of use but again, this car will not see much track time and temperatures are controlled by correct fuelling (=pretty rich compared to watercooled world) and timing. That's where twin-plugging shines: it will let you reach MBT without going into deadly detonation area and close to MBT means lower EGT's. With single plug and retarded ignition angle you always have high EGT's. Dumping fuel is a band-aid but a buit too much and EGT's will rise again, this time burning exhaust valves and turbine wheels.. I remember reading somewhere in pelican that twin-plugging is not a great advantage with boost. I don't remember who said it but it is so untrue. When you don't let the engine detonate and does not let EGT's to go through the roof, the heads hold up fine. I was toying with the idea of using VGT turbos but they are readily available only in sizes that don't appeal to me. HE341VE (basically HX35 with VGT turbine) or HE351VE (HX40 with VGT) are great turbos flowing 600 and 800 hp worth of air but they weigh around 20 kg's and I don't want that weight in the back of 911 :) Current ball-bearing IHI's weigh only 3.2 kg's each and still give up to 600 together. I'm aiming around 400-450 which should be more than enough on ~1000 kg 911 (stripped but witl roll bar). Hydraulic TOB is a no-name product I bought from my friend. He has used them on his Mercedes manual box conversion projects with great success (on V8 motors he needs custom flywheel and clutch solution). Mounting needs a machined aluminium block only but this will be addressed when I finally will be installing the motor. That is maybe after year or two, because body needs to be sorted too. Here's RS 90mm pistons and cylinders. They need some clean-up as they are covered with some greas for storage. http://www.porsche-foorum.org/album/...l_kolvid24.jpg And here's photo of how the pistons are lightened from inside the dome. I personally would not probably have done it but they appear to be done very well and all of the pistons are within 0.5 grams (weighed with the lab grade scales at work). http://www.porsche-foorum.org/album/...al_kolvid4.jpg Regarding sealing rings between heads and cylinders, would you recommend something better than stock ones? I remeber having read about Ni-resist or something? Could you explain what's behind it? Thanks! |
My friend has the information about the hydraulic TO bearing in his website: Elbe Engineering - Hüdrauliline survelaager
http://www.elbe.ee/products/bearing/survelaager2.jpg http://www.elbe.ee/products/bearing/survelaager.jpg |
Exciting project.
Subd |
Quote:
Scott |
No updates for quite some time but it's moving, albeit slowly (few things happened meanwile, like wedding, honeymoon, building other peoples cars etc).
The heads are now done, ported, twin-plugged, with new guides (poly-bronze), stem seals, full radius seat cut etc. Will take some photos after I go to the garage again. I also prepared the turbos, though the compressor housing could use some stronger cleaning agent to get the best look. The turbos are IHI RHF5 series, ball-bearing and water cooled units, capable of ~300 hp each. I have one running on my turbocharged 924 and it makes 220 hp at the wheels on pump gas (9.3 CR) and 235 rwhp with 30% mix of Toluene. http://www.porsche-foorum.org/album/...rmal_IHI_1.jpg The turbos are easily clockable to whatever direction of compressor or turbine outlet is needed. http://www.porsche-foorum.org/album/...rmal_IHI_4.jpg I deleted the integrated wastegates by threading the wastegate ports and making plugs for them. I'm going to use a Porsche 931 single wastegate with special wall in order to separate pulses until wastegate opens. http://www.porsche-foorum.org/album/...rmal_IHI_3.jpg Also plugged the wastegate shaft openings. http://www.porsche-foorum.org/album/...rmal_IHI_2.jpg |
Long time no update but here's a quick view of the "umbrella" that will be hosting this engine:
http://www.porsche-foorum.org/album/...sche%20006.jpg Side skirts will be deleted though and air inlets are also already present in rear quarterpanels. |
What rear fenders are those?
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The rear fenders are replicas of those from 934. Previous owner (my friend who died in car accident few years ago) made the molds from original 934 flares. There is some alterations from original but they look very nice.
I'll be changing the wheels. At the moment there are Speedline Corse LeMans Type 2017 magnesium wheels 10x18 and 11x18 but I don't need such hardcore wheels and opt for BBS RS ones. The Speedlines are brand new, there are total of 7pcs of them and I probably will sell them. I'll take some photos of the rest of the car also, it has completely redesigned suspension with raised suspension mounting points, 968 alloy arms+951S brakes and coilovers. |
Beautiful stuff here can't wait to see more. This gives me a lot to aspire to....... One day.
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Subscribed :-)
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Any updates?
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Have you thought about using smaller cams than the "S" ones you mention? If it's mainly a street engine you'd probably have nicer off-boost response with milder camshafts. Cool project!
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Matt:
No, because of several reasons: 1. I already have a nice set of S cams, 2. Other (user aws) have used them with success 3. I will use programmable EFI with ITB's and can also fine-tune the intake length on the dyno to have best results which will tame the engine. I am hoping for ~400-430 hp @ 1bar with redline at ~7400-7500 max. The turbos shoul produce full boost already at ~4000, so ~3500 rpm usable powerband is already MUCH better than most similar hp/liter NA engine. Thanks for compliments! Regarding updates, at the moment I'm focusing on the chassis and preparing it for the paint job as my friend will have a window where he can take my car in. Will get some updates regarding engine soon enough I hope. |
Looking forward to seeing it run!
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Haha, it will run for sure but the expectations regarding power etc need to be verified by real world results :)
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"Back in the day" in there were cam manufacturers that would produce 'turbo' cams that had 0 overlap, using the logic that it was wasteful to blow your intake compressed intake charge straight into the exhaust. I don't think anyone subscribes to that logic any more.
But taking a quick look at the "S" profile at Dougherty Racing Cams Porsche 911, 930 and 964 camshaft profiles I notice that it has more duration and narrower lobe separation than the 3.8 Super Cup cars and the GT Evo. It seems 'wrong' that a relatively small displacement plus turbo would like a smaller cam, but with the ITB's and good tuning perhaps it will work great. I've ogtta get me a project car to start playing with these things again... :) How long until it's up and running? |
Everything in this life is a compromise and since there is nothing rational about any serious sports-car let alone a short-stroke turbocharged 911, I think using S cams even just for experimenting would be pure fun.
Since I'm not going to chase every tenth of a second on the track against competition, only track days and just fun-driving on the back roads, what would be better than wild and fire-breathing old 911 :D I started the build of this engine prior to reading this thread: http://forums.pelicanparts.com/911-engine-rebuilding-forum/535136-smaller-stem-valves-46-40-heads.html ...but reading that assured me that it sure will not be a dissappointment, at least if I don't make obvious error in the assembly. Also, iirc Steve Weiner also has experimented with small displacement turbos, not sure what cams he used. As for completing the build, it is unclear at the moment since I have my track car to drive and redesign (currently in the process of fabricating new turbo exhaust manifold) and also hot street 924 for my wife (2.5liter 16v turbo with 951 suspension+brakes etc). But, the process is ongoing and has not stopped yet! |
Keep us updated. Sounds like a coo project.
Just bought a 914 wih a 2,2 911 engine. Also thinking og turboing that engine. This is a cool build 1973 Porsche 914-6 2.1 Twin Turbo |
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