dynamic compresson test? help please
Discussion
I want to accuratley measure my dynamic compression ratio across various engine speeds and throttle openings. I would like to do this myself by hiring the correct piece of kit. Has anybody done this and did you get any meaningful results.
My thoughts are that I would remove the sparkplug, disconnect the injector plug and fit the tester into the plug hole then start the engine and run at a variety of speeds.
The standard analogue compression testers do not seem to work well under these conditions. By the way its a 4.5ltr AJP.
My thoughts are that I would remove the sparkplug, disconnect the injector plug and fit the tester into the plug hole then start the engine and run at a variety of speeds.
The standard analogue compression testers do not seem to work well under these conditions. By the way its a 4.5ltr AJP.
Blimey, this is bit outside your normal garage requirements
This usually requires installing pressure transducers into each cylinder and an optical encoder onto the crankshaft, the transducers are about £1000 apiece and the AVL kit to log the data another 20K. You can get trandsucers which fit into a custom spark plug but even so this is a fairly involved operation.
Even if you want to measure a cylinder that's not firing and without any crank reference you'll still need a fast data logger however the pressures won't be representative as combustion sets up a much stronger pressure wave than non-combustion.
This usually requires installing pressure transducers into each cylinder and an optical encoder onto the crankshaft, the transducers are about £1000 apiece and the AVL kit to log the data another 20K. You can get trandsucers which fit into a custom spark plug but even so this is a fairly involved operation.
Even if you want to measure a cylinder that's not firing and without any crank reference you'll still need a fast data logger however the pressures won't be representative as combustion sets up a much stronger pressure wave than non-combustion.
Maybe I should mention that the reason that I wish to do this to look at the viability of fitting a rotrex supercharger. One area I have is that even at relatively low boost around 5psi I may suffer from detonation. The specified CR is quiet high on this engine but I would like to know what the actual CR really is.
Yep, unless you're planning on making a kit and selling a few hundreds at a large mark up you'll never recoup your costs from buying the kit.
It'll be much cheaper to reduce you static CR by 1 and then fit the Supercharger and either up the boost or raise the CR from that point.
Surely if it knocks just wind the Ignition advance back.
In cylinder pressure measurement really only assists you when determining max cylinder pressure from combustion/knock events and checking whether you rods/pistons are capable.
It'll be much cheaper to reduce you static CR by 1 and then fit the Supercharger and either up the boost or raise the CR from that point.
Surely if it knocks just wind the Ignition advance back.
In cylinder pressure measurement really only assists you when determining max cylinder pressure from combustion/knock events and checking whether you rods/pistons are capable.
The kit is really only meant for me, I'm not planning to retail any parts. What I really want to do is establish the condition and spec of my engine, just by reading other threads on this forum it is obvious that these engines differ somewhat in their spec's
I know it would be best to lower the CR, upgrade the pistons, strengthten the rod's, fit better head gaskets etc, etc but is it actually necessary, half the forum says yes it is and half so no its not. (in a low boost application).
Maybe I should get the car up on a good engine analiser / rolling road and get them to report back on the current condition of the engine before I decide whether it's a viable project. It's only done 30K but if it needs a rebuild then the supercharger project will go out of the window.
On that point does anyone know a really good place to get this done near Reading?
I know it would be best to lower the CR, upgrade the pistons, strengthten the rod's, fit better head gaskets etc, etc but is it actually necessary, half the forum says yes it is and half so no its not. (in a low boost application).
Maybe I should get the car up on a good engine analiser / rolling road and get them to report back on the current condition of the engine before I decide whether it's a viable project. It's only done 30K but if it needs a rebuild then the supercharger project will go out of the window.
On that point does anyone know a really good place to get this done near Reading?
A dynamic compression test with open throttles at cranking speed combined with a cylinder leak down test will give you a good idea of the condition of the rings/valve seats.
If I were going to the lengths of fitting a Supercharger I'd have the engine out and overhaul it anyway.
If it's a low boost app then just wind the ign back if it knocks. A low boost on N/A compression isn't going to be optimised anyway.
If I were going to the lengths of fitting a Supercharger I'd have the engine out and overhaul it anyway.
If it's a low boost app then just wind the ign back if it knocks. A low boost on N/A compression isn't going to be optimised anyway.
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