Can we safely run our cars with 11.5 compression ratio?
05-25-2001, 01:34 PM
#42
I am doing it as we speak. The cam timing can be further advanced by grinding advance into the primary lobes. I am going for close to the spoon specs with 5 degrees of advance to compensate for the head being closer to the crank. Any oppinions are appriciated. BTW the reason I am cutting the head as opposed to using a gasket is because this way I can remove as little material as I like hence making whatever compression ratio I want, in this case 12.1:1. Also I am grinding the cams but not adding (re-grinding) metal to the cam. I am aware of the heat treating of a hollow cam as well as the harmonic issues associated with 9000 rpm on the cam shaft. The guy machining my parts knows his shit, and has spent 2 months just testing things for optimum levels. He is tuning the whole set up, from the TB to the CAT so this should work well. If it blows up I will re-build with all Spoon parts, if all goes well, Ill post dynos. Wish me luck!
05-25-2001, 03:26 PM
#44
Registered User
Wow, I get one little rolling blackout and look how much you guys have talked about! :-)
First, our cam gears are not adjustable stock. However, adjustable cam gears can be created, and are in development as we speak. Right now the source I know is obtaining production samples from large scale manufacturers to determine who will be the producer. The design is quite elegant, but the added complexity of the F20C cam drive will mean they cost noticeably more than traditional DOHC adjustable gears. You would not be able to easily do an offset pin on it. I _may_ be the guinea pig vehicle, but we'll see.
Second, mdgrippa, get whatever you can from the headgasket, and then think about milling. You can't put metal back on the head once its off. A JDM gasket will get you 11.7:1, then another 0.010" milled would put you at 12.1:1 (or just use the Spoon gasket for 12.2:1). Believe me, this is by far the preferable alternative. Additionally, milling the head does not do anything to improve your quench area, but a thinner head gasket does reduce the quench distance, which can improve combustion efficiency.
In terms of ignition timing, the ECU reads and sets this based upon the crank angle sensor, so whatever happens with cam timing or deck height, ignition timing will remain the same. There are sensors on the camshafts though which determine when to start the fuel injection event (which makes sense, don't want to spray it before the valve is opened).
Because the F20C has a knock sensor, timing will naturally be retarded if detonation is detected, whatever the cause.
cdelena, on this engine, every 0.010" is about 0.4 points on the compression ratio. We really don't need to know the chamber volume (which is useless without knowing crevice volume, piston dome volume, etc.). What we know is that with a 499 cc swept volume, the total combustion volume has to be about 50cc to get 11:1 compression. Knowing the bore of the cylinder (and that the chamber has recessed quench) allows us to determine the volume reduction for each decrease in gasket thickness.
Finally, as I stated before, a modest retard of the cams make actually help power on this engine, which could explain part of the supposed gain for the JDM engine.
UL
First, our cam gears are not adjustable stock. However, adjustable cam gears can be created, and are in development as we speak. Right now the source I know is obtaining production samples from large scale manufacturers to determine who will be the producer. The design is quite elegant, but the added complexity of the F20C cam drive will mean they cost noticeably more than traditional DOHC adjustable gears. You would not be able to easily do an offset pin on it. I _may_ be the guinea pig vehicle, but we'll see.
Second, mdgrippa, get whatever you can from the headgasket, and then think about milling. You can't put metal back on the head once its off. A JDM gasket will get you 11.7:1, then another 0.010" milled would put you at 12.1:1 (or just use the Spoon gasket for 12.2:1). Believe me, this is by far the preferable alternative. Additionally, milling the head does not do anything to improve your quench area, but a thinner head gasket does reduce the quench distance, which can improve combustion efficiency.
In terms of ignition timing, the ECU reads and sets this based upon the crank angle sensor, so whatever happens with cam timing or deck height, ignition timing will remain the same. There are sensors on the camshafts though which determine when to start the fuel injection event (which makes sense, don't want to spray it before the valve is opened).
Because the F20C has a knock sensor, timing will naturally be retarded if detonation is detected, whatever the cause.
cdelena, on this engine, every 0.010" is about 0.4 points on the compression ratio. We really don't need to know the chamber volume (which is useless without knowing crevice volume, piston dome volume, etc.). What we know is that with a 499 cc swept volume, the total combustion volume has to be about 50cc to get 11:1 compression. Knowing the bore of the cylinder (and that the chamber has recessed quench) allows us to determine the volume reduction for each decrease in gasket thickness.
Finally, as I stated before, a modest retard of the cams make actually help power on this engine, which could explain part of the supposed gain for the JDM engine.
UL
05-26-2001, 05:47 AM
#46
Registered User
UL, Are you positive that it's not adjustable? I know the intake/exaust relationship is not but that main driven sprocket should be. Or rather not continously adjustable but at least 3-4 offsets to compensate for chain stretch?
Such a marvel of an engine should not be without that feature.
Im looking at this picture, the sprocket is bolted to the drive gear, maybe if not pinned the bolt holes themselves are offset so a simple rotation and remounting will compensate?
[Edited by cmnsnse on 05-26-2001 at 06:49 AM]
Such a marvel of an engine should not be without that feature.
Im looking at this picture, the sprocket is bolted to the drive gear, maybe if not pinned the bolt holes themselves are offset so a simple rotation and remounting will compensate?
[Edited by cmnsnse on 05-26-2001 at 06:49 AM]
05-26-2001, 12:33 PM
#47
JDM definitely has a different ECU. Even Mugen do two versions of their ECU to allow for JDM and ROW. I would expect the ROW ECU to have problems with higher compression which may negate any benefit.
05-27-2001, 06:42 AM
#49
If this is true, then i should be able to run a JDM ECU such as a Spoon or BYS with no problems. Mabey compression is the reason that these ECUs do not work on our cars stock?
