It's All About Compression

January 12, 2006

Ok

I might be wrong but this notion has been bugging me recently. I was reminded about it when I answered the phone for a group of colleagues who where in the motor vehicle workshop. Some bloke wanted to convert compression ratios into 'lbs/square inch'. I told him he was talking to the physics lecturer but I could help him. I gave a very detailed calculation which lost him after the first algorithm then told hime after a muffled giggle on the other end that he could probably get away with multiplying the atmospheric pressure by the ratio and that would give a ball park figure. I then told him that each cylinder should be checked and the highest reading should be used as the datum.

I then started remembering my old days of tricking out motorcycle engines and a fate that happened to one fool with more money than sense.

He took a turbo from a GPZ750 Kawasaki and attached it with all the wiring and ecu's to his N/A GPZ900. He got it all working ( so he had a modicum of imtelligence). He took it out and was going to show off in front of a large group of fellow bikers how good it was (he had taken it easy on the first day to run it in.

He went charging up the dual carridgeway at full bore. The turbo clicked in, the front wheel raised, the speed increased dramatically as did the revs, the engine disintegrated with an almighty bang! The carridgeway was littered with engine casing bit, connecting rod parts and piston ring fragments.

He totalled, what was at the time, the quickest production bike money could buy (it was still under warranty) as if a 0-60 time of 2.2 seconds and a top speed of 160 wasn't enough!

The bloke was taken to hospital as a piece of hardened valve seat went into his leg causing a nasty gash.

The main difference between turoed engines and non-turboed engines is the compression ratio. If a non-turbo comp ratio is say 10:1 then the turbo version of the same engine will have a much lower compression ratio say 7:1.

To cange to a turbo then differnt low comp pistons need to be fitted otherwise the engine will blow and you know how easy it is to blow a Supra head gasket!

Changing from N/A to turbo is very involved and very very expensive. It would be cheaper to get a complete engine change.

I bet most of you know this but it gave me the chance to tell you a good (although financially awful) tale.

Regards

Michael

January 13, 2006

lol , great story.

baz

January 13, 2006

It IS however doable at low boost!!!!!!

It varies from engine to engine... but most DECENT engines (read decent engineered to withstand stresses way over those produced at stock power) could take at least 6 psi of forced induction before they go pop.

There are a few supra "N/A-T"s (as they call them stupid name).. they are essentially a lightly blown n/a lump... this works well because they have the bottom end torque of an N/A engine, with the obvious advantages of turbo power later on... if you know the limits of the engine, and stick withon them it can be most effective!!!!!

I am planning on building an N/A engine with turbos stuck on...

The 1UZ-FE has been documented to run at 600 bhp, reliably, with just forced induction and supporting fuel mods bolted onto it....

HKS' Best selling turbo kit is the one that converts the mx5 from n/a to turbo... no internals are included :D