Hey guys i was thinking about raising the compression of my engine instead of forced induction. i know i will need pistons custom made, but is there anything else that needs to be done? also does anyone have approximate gains by doing this? any help would be appreciated. just to let you guys know, this is only the beginning of my thought process, nothing is final. I know people are going to tell me to just turbo but please dont. i really would like to understand what has to be done to get a higher compression. thanks

 

How much of increase?

Increasing CR will grant you HP/TQ throughout the powerband. More stronger pull.

Just like VW w/ its 5 valver per cyl . . . . great midband TQ.

 

thanks, im not really sure. is there a maximum i can increase it? i dont really know much about it but i was just thinkin bout it. would i need any other work like custom rods?

 

CR is easier to be raised through domed piston head . . . you might not want longer rods, give you more stroke but at the expense of rpm.

For example of domed piston head, look at the 4g92 Mivec. It's severely domed.

10.5:1 maybe tolerable on 93 octane gas. 11.0:1 is absolute max for street use. Anymore than that, you have to fill the tank w/ racing gas.

 

eh....higher compression on a 4 banger is not really a good way to increase power. even tho it will pull more throughout the powerband its still not efficient. high compression is better for 8 cylindars since their RPM's are really low.
i mean...if you going to really spend the money to rip apart the motor you might want to try something different. buuut you could get away with 10.5:1 and do a lot of head work, new cams, valves, springs, rocker arms...that should increase power a lot. all motor power is greatly respected too..

 

economically, raising the c/r is not a good idea. its extra stress on the engine, less than stellar power gains, and definitely is not cheap. Worst of all, it has a physical limit on how much u can actually do.

Arguably, the wider/broader torque band is very attractive. And being able to say its all n/a power is also very fun. Personally, I wouldnt, but if youre going to, its a long painful road ahead.

(but why would u ever consider giving up the symphonic BOV?!? *pshooosh!*)

 

If you're looking at rods with higher compression, all I'd want to do is beef them up to not only try and raise the redline (long rods = low redline but nice torque) but to also handle the higher compression. Then you gotta add all the other fun happy things (head work) to take some serious advantage of everything.