: Turbocharger question



davesdeville
11-18-03, 10:46 PM
I was reading about superchargers and I came accross this page:

http://holley.com/HiOctn/TechServ/TechInfo/SCTech.html

Scrolling down, I noticed the effective compression ratio chart and I got to thinking. People run turbos at 30+ psi and Ive seen turbodiesel trucks running at 60+ psi boost, how do they do that without having detonation problems?

03EscaladeAWD
11-19-03, 02:46 PM
I don't know much about diesel, but don't they already run a higher compression ratio? And they detonate on their own, they're supposed to, no spark plugs. My question is how can the engine handle it.

Stoneage_Caddy
11-20-03, 05:41 PM
I don't know much about diesel, but don't they already run a higher compression ratio? And they detonate on their own, they're supposed to, no spark plugs. My question is how can the engine handle it.

a gasoline turbo engine has reduced compression from its stock counterpart , where a regualr nissan sr20de has 9.5:1 a full blown sr20det has 8.5:1 and makes anywhere from 7-17 psi . changes are also made in the fuel delivery side, a sr20de has 4 injectors that are around 270-320 cc where a 210hp sr20det has 4 370 cc injectors running a diffrent cycle and more fuel pressure (440cc for the 240+ hp det), this excessive fuel helps cool in combustion chanbers and air charge , speaking of cooling intercoolers are also critical to keep the compressed air temps down , name of the game is to keep everything as cool as possible to avoid detonation

a diesel operates soley on detonation , the high compression raito of a diesel create tremdous heat which cuases the combustion , ive seen a few times a reduced compression ratio but more often i see changes in injector timing and injector size , the injectors only are fired when the engine is ready for combustion (similar to a gas engines 10 degrees btdc) , since there is no fuel presnt on most of the compression stroke detonation is pretty rare

basicly instead of a sprakpug sparking at the right time we have a injector squirting at the right time

engines are built up to handle the added mean effective compression ratio thru all kinds of things from going to cast iron heads to diffrent head gaskets , also commonly seen is oil squirters the keep the pistons cooled beatter , once again , keep everything cool and the critter will survive

you will also hear about mean effective compression raitos when people talk about varible valve timing , by chageing the duration of the intake cam you efficly reduce its comression ratio , the 11.5:1 engine in the celica rarely runs at its full 11.5:1 , most of the time its making around 9.5:1 to 10:1 and the full 11:1 comes on as the computer sees fit , ususly at W.O.T....... running a lower compression ratio allows for beatter emmisions and lower gas milage