slate blue

Well I had an interesting morning this morning, I was having a chat with a young engineer over from the Porsche factory, we were discussing the Ferrari F1 engine and then got onto the Carrera GT to which he knew a lot about. Quite amazing really, the engine testing that is, I couldn't imagine 100 hours under full power and load. I don't think I would do that to my car. But it passed its tests.

Then we were discussing my project, he was worried about two things, now for those who don't know mine is a stroker project and I am now commited to it as I have already bought some parts. He was worried about the short rod to stroke ratio, thought it would have an adverse effect on the BMEP. I am going to provide him with some of the details of the Kelly Moss engine, to which he was interested in. He was also concerned about the exhaust ports cracking, I told him I also had concerns and I was going to implement at minimum the GTS modifications which he liked, he told me the Cayenne had a more advanced but similar system.

I discussed ceramic coatings, he was worried if it started to delaminate engine would occur. Some I suppose that is an area I will have to deal with in the future. Then he said of his friends has a 928 and also was an engineer, and he told how he built a variocam engine. I said" you know that fellow in the States" With the 968 style Variocam.

No he is German, his engine is really quite advanced, his engine also varied the lift also. Just picture my jaw dropping at this momment. "O.K. well how did he do that?" I asked.

He has three cam lobes for every valve. O.K that's like Hondas V-TEC, "No" came the response. "Porsche experimented with this 30 years ago." Well that is something I didn't know that is for sure! He said the torque from that engine no matter what the revs was really strong. I also mentioned the problem we have with gearboxes and that you can have too much of a good thing. Yes he agreed the gearboxes are quite weak in the 928. We were only dicussing the manuals. But he agreed the GT and GTS boxes were certainly the pick of the crop.

Well there you have it, thought I'd share that, cost me a bit a time but it was certainly interesting.

Lagavulin

Very interesting, thanks for sharing!

What is your ratio?

Porsche is also currently running the system in the 996 and 997.

blau928

Hi Greg,

Thanks for sharing..... I am very curious on the rod/stroke ratio... What length rod are you using, and what stroke are you using, or what ratios above or below did he become concerned about...... I will be building a stroker as well, and would be interested in his comments.

Regards,

heinrich

How to contact the variocam guy?

Kevin in Atlanta

That would be Sterling Gee. Search this forum. Very cool project. Spent $$$!

heinrich

Tiburon, read it again ...

Shane

Doh! I almost jumped to the same conclusion, then saw the variable cam lift.

slate blue

O.K. to answer the questions about my rod ratio, it is just the standard that most are using. 3.75 inch stroke and 5.85 rod length. this gives a 1.56 rod to stroke ratio. Now the standard rod to stroke ratio of the existing motor is around 1.9 and is almost the same for the GTS. If I dropped the stroke a touch and went for a 6 inch rod which are quite common the ratio impromes about 20% to 1.67 this with a 104 mm piston gives a 6.2 liter. I can live with this. One of his other comments about the short rod ratio was higher friction and that the skirts of the pistons should be coated to reduce this.

Anyway I will supply him as much info as I can, he is going to run some sums for me inrespect of my trumpet length for the individual throttle bodies. Also he wanted to see if he could work anything out from the figures of the Kelly Moss engine. If anybody has these please post them. What I believe I'm missing is the engine speed at which the power readings occurred.

Yes when I email him I will asked for as many details and or photos of the V-TEC as he can muster!

blau928

Greg,

Thanks for the info..! FYI, so far, my plans call for a 1.6 ratio using the stroker crank, with pistons coated etc.. Did he mention how adversely the wear of the components or BMEP was affected with the variance in ratios? In addition, did he mention anything on cyl. head parameters? Keep us informed.

Thanks,

slate blue

I will certainly keep everyone informed, any info from people who have run these strokers would of course be highly valued. I am concerned about wear rates, but I would have thought with our highly durable block material, whether it be Nicasil (my current plan)in my case or Alusil in others, this is a slow wearing low friction surface. I'm just wondering since I haven't had my block Nicasiles as yet, whether DLC coating the piston skirt may be the ultimate solution. I know they are experimenting with this in F1 engines.

The DlC is said to have a lower friction coeffient than the nicasil, Nicasil is better at retaining its oil though. But maybe this isn't nessasary with the DlC coating. These coatings almost drop friction to zero. They are used extensivly in F1 and are said to make parts almost last forever, how long is forever in F1 anyway! LOL. Seriously the wear rates are as low as the friction, the finger followers on the Ferrari F1 engine are coated and it is said that they wouldn't last 10 minutes uncoated.

blau928

Greg,

What's the DLC Coating you're talking about..? I know that some racers use Casidium coated wristpins, and Mahle's engineer I spoke to recommended only their coating/process for the pistons I want to use in ALUSIL. In Nicasil, or sleeving the block, there are many many more options... (I was thinking of asking some of my contacts in the Nanotechnology field to shed some light on the molecular bonding of some slippery stuff once I got further along... They have made some good progress in this arena..)

Thanks,

rob rossitto

thx for updates greg! IMO, and from what I've seen, don't think the .15" is significant for NA street cars, as devek has an excellent rep for reliable strokers w/mahles and their 3.75" cranks...many have followed w/decent results also... you CAN use 6" w/3.75" and a nicom/custom piston - the 968 CH is about 1.420" already, so you don't have a lot of room to play with, but w/6" rods and decent ring seperation the oil ring w/be in the upper pin area so you'll have to use supports... as long as you don't use chrome supports (a no no in the Nicom) and keep at least .250" from piston top to comp ring, you're fine according to JE... for me, it was not worth the extra PITA factor, but you guys are going to be pushing a lot harder so it might be worth it...

coatings sound cool...pls keep us posted, my motor is in early fitting stages now, bearings are already being coated using Nascar stuff, but DLC sounds interesting.... I'd have to hurry to get it done asap if I do it though, as I'd like to see this finished before I'm dead/too old to enjoy it/etc...

G-day!

slate blue

Thanks Richard thanks Rob, I have already bought my pistons, as such I'm stuck with them. I do take the point about Devek, and they can chime in here if they like too. I someone would post it for me I have some iinfo on the different length connecting rods and rod ratios. As I said all I can do now is cut down the stroke a little. I don't know just yet if it is worth it? I will give this fellow all the facts and see what he can come up with. He did ask what are people doing successfully, he was certainly interested to know, he was just prepared to say that will be no good. Can somebody try and get the Kelly Moss details?

Also has anybody got a picture of the stroker crank? Beit the Moldex or Scat, he said he wanted to have a look at it. The reason was he wanted to see what if any, pin overlap it has. Richard the reason I didn't go into DLC or Diamond Like Carbon was that I had already posted it here bofore. They are using this material more and more in high tech engines, I know it is used extensivly also in Nascar engines. I was certainly going to use it if I got my camshafts welded up. Because the friction is gone essentially that means welded cams will last.

If you want to keep up with this stuff you need to buy a magazine called Race Engine Technology, it comes out four times a year. The details I have for the Kelly Moss engine are 711 HP and 680 ft of torque, I need the engine speeds for these figures. Also I believe this engine is a 6.4 or 6.5 Liter, if I'm not correct, feel free to chime in.

My approach to the throttle bodies is this, when they come out in Australia, the new M5 that is I will see if they can be adapted. From the photos it does look promising. I will place my top injectors into the trumpet, so that they point directly down the port, I got these pretty trick injectors for the 2004 Suzuki GSX-R 750 They are multi hole injectors.


So if the basic shape and layout is correct I can make an investment casting and modify other minor things at the time. I may have to buy two throttle bodies to do it though.

Also just have a look at this fabulous exhaust, it must be the type they make flat and then heat up and blow up the pipes when red hot.

Louie928

Greg,
If you want some info on individual TB runner lengths, maybe I can help. The total runner length from the cylinder head mating surface to the top of the inlet trumpet is about 210mm on my individual TB system. The TB diameter is 50mm. This gave a torque peak at about 5200 rpm on Marc Thomas' stroker motor. That was with his (Devek) B1 cam. During initial testing, Marc didn't want the torque to go beyond 500 lb. ft. so the timing was retarded around the torque peak rpm to keep it below 500 lb. ft. We ended up with 485 lb ft @ 5200 and approx 545 hp @ 6000. This was RWHP on a Dynojet. The torque was still pretty flat at 6000 so the hp peak would be at a higher rpm. The purpose of the test was to see if the individual TB setup was worthy of further development, not to get maximum power. We didn't want to test above 6000 so quit there. I plan to use shorter intake trumpets to further reduce torque and allow for better packaging under the hood. I'm not sure there is any advantage to go to the trouble of a vario cam since the (Devek) 6.5L makes plenty of torque to shred gears as is.

slate blue

Thanks for responding Louie, I agree whole heartedly about the torque issue, you can have too much of a good thing. That throttle body setup did produce massive power so congrats on that one. The B1 cams if I'm not mistaken have a maximum lift of about .440 inch? I'm certainly not chasing any more power than what is on offer here. I don't need to be king of the horsepower tree, the rest of the driveline just can't take it. Nor can you probably use it anywhere but a track.

For me what it provides is the power to be competitive and be able to rub shoulders with the current day exotica. I don't think any of the topline cars produce as much power as your throttle body setup did. The most powerful is the Ferrari Enzo at 660hp. I will ignore the Konigsnegg or however you spell it as it is somewhat untested. Given one of the things Porsche does quite well is R&D. The fact that the Carrera GT engine can run 100 hours under full power and load surely says a lot. I wonder how long these strokers can run? Anyone want to hazard a guess? The areas that would worry me are the short rod ratio and the exhaust ports cracking. But maybe they are just worries and with the proper treatment may amount to nothing. I don't want to be worried about a grenading motor.

A few other points of interest, the Carrera GT engine has the inside of the piston crown polished, also a GT3 engine without its special treatment of the throws on the crankshaft and with the drysump disabled lost 45 hp @ 8000 rpm.

Hope this is interesting. I will seek more info for us all.