Tyler06 266 Posted June 8, 2013 Hiya all, just wondering what sort of difference i will see/feel by dropping my comp.. My engine had 11.8/1cr but i am dropping it down to about 11.1/1cr with the new block. Only reason being that i want the cast piston to last a bit longer whilst i build a new bottom end which will take 12-18mnths. Still wanna get times from this one then compare ;-) much of a difference ya reckon? Share this post Link to post Share on other sites
gerg 10,871 Posted June 8, 2013 I personally think there will be stuff-all. I reckon you're still in the danger zone for cast pistons, that is if you're not running a lumpy enough cam to bleed off some compression. I'm guessing though that you don't have such a problem with detonation as you would have mentioned it. Share this post Link to post Share on other sites
mcfly94 169 Posted June 8, 2013 out of interest what are the limits on casts? Share this post Link to post Share on other sites
Tyler06 266 Posted June 8, 2013 I do have a pretty lumpyish cam lol but when it comes to casts and there limit it has more to do with wat comp and the detonation factor as far as i get it. Inc running too lean etc. my engine ran beautiful with my last tune but i had dramas where it would only start on 26* advance. Had it ramping up to 32* and it didnt ping. I stripped my wiring harness and found that my dizzy power supply was only supplying 9v. Change that and then it would start on 12* but hated anything after 26* and pinged real bad but up until it pinged it felt so much more healthier and smoked my tyres like they were 155s. My stall is rated at 4400 but it just went from 2000- 4200 in a heartbeat and smoked. I am changing my castys in my new bottom end but for now they need to last so im only dropping my comp to stop the pinging. Share this post Link to post Share on other sites
gerg 10,871 Posted June 8, 2013 out of interest what are the limits on casts? It's all relative, as in what cam and fuel you're running but for a mild-medium cammed streeter running shitty 91 fuel I wouldn't go above 10.5:1 with cast pistons. That's just me, as I like my engine to hang together for 300,000 k's and not do any surgery. I think i'm getting old. Some are happy freshening up an engine every 50,000 so and don't mind running on the ragged edge when it comes to cams and compression, etc. Horses for courses really. Share this post Link to post Share on other sites
Clevo120Y 815 Posted June 8, 2013 I'm going to go out on a limb here and predict that it will perform better, I think you will get a more user friendly tune into her. Share this post Link to post Share on other sites
PRO250 1,506 Posted June 8, 2013 my engine 3 years ago i went from 12.6 to 11.3 it seemed the same to drive and made the same numbers on the dyno and you could run more timing with no issues 2 Mixalis and Clevo120Y reacted to this Share this post Link to post Share on other sites
Tyler06 266 Posted June 8, 2013 It will all come to a head wen i get it all back together. It seems ive been failing since the first time i started this thread. Def hope it works out this time! Share this post Link to post Share on other sites
Tyler06 266 Posted June 8, 2013 Wrong thread same situation! Share this post Link to post Share on other sites