Turbo and Compression

[China]

correct me if i am wrong, but it is a LOW Compression Ratio that you seek if you wish to turbo charge a car and a HIGH Compression Ratio that you need for a Natural Aspiration. i think that the ka24de is 9.5:1, and i believe the Honda b18c5 is something like 12.5:1 (or something). i just got a little confused and in need of some direction.



thanks
china

[99B16Si]

i have no idea what a KA motor is compression wise but a USDM ITR (B18c5) IS 10.6:1. as far as boost goes, generally speaking, if you lower the compression ratio of a motor it allows you to run more boost and ignition timing on pump gas. higher compression just helps for out of boost power and spool time.

[Sneakin Deacon]

yea, there is a fine line when dealing with the static compression ratio. too low and the car will be a dog daily driving...to high will limit you somewhat to the power you can make.

[Jordan Y.]

It depends on what application you're talking about. Factory turbo cars tend to do well with between 8:1 and 9:1 compression, for a good balance between off-boost response and spool and ability to run more boost. I'm personally going for forged 8.5:1 Ross pistons when I build up my spare engine, as opposed to the 7.8:1 stockers. On Honda turbo setups (which I don't know as much about), I see them run higher compression ratios, usually 9 as a minimum. Considering the relatively large turbos these 1.6's and 1.8's often use, not spooling until mid 4k range in some of the dyno charts I've seen, lower compression would probably completely kill any off-boost power the cars have.