9.5:1 compression, to low for a N/A motor??
10-25-2010, 11:11 PM
#1
2nd Gear Member
Thread Starter
Join Date: Apr 2009
Location: Illinois
Posts: 422
9.5:1 compression, to low for a N/A motor??
Well i just found a good deal on a fresh 351w on craigslist, i got the part numbers for the pistons off the seller and found out the compression ratio would be 9.5:1 with 60cc heads, which i was going to use. Is this to low for the N/A motor? Sorry if this is a ignorant question but i dont know much about compression ratios, and i dont want to put the thing together and have it be a dog in the spring. What do you guys think?
10-26-2010, 03:01 PM
#4
6th Gear Member
Join Date: Nov 2006
Location: Spfld, MA
Posts: 9,240
9.5 is a perfect street ratio for N/A. Stock 5.0's came with 9.0:1. You'll be able to run the **** out of it, while using pump gas. Any higher ratio, and you're looking at octane additives to remain in a safe range.
10-26-2010, 06:42 PM
#5
3rd Gear Member
Join Date: Jul 2007
Location: Sandusky,OH
Posts: 893
Youll be fine,as stated any higher your gonna have to run a high octane fuel,My motor is 9.7:1,and I spray mine,without the nitrous its street manners are perfect. I run pump gas in mine(93oct) and spray 125.Runs like a beaut.
10-28-2010, 12:50 AM
#6
6th Gear Member
Join Date: Apr 2007
Location: California
Posts: 10,468
Compression and cam work together. 9.5:1 can still let you run a healthy cam up to 6,500rpm easily. Also engines make quite a bit more power with more timing and less compression than they do with less timing and more compression. With more modest compression and the correct cam, you can run a more aggressive tune safely on pump fuel than you could otherwise. The extra timing will give you more power over a wider rpm range, better throttle response and better mileage.
And just fyi, most new factory cars are running the 11:1 and 11.5:1 ratios for part throttle mileage. At part throttle you're starving the cylinders to breathe, so they barely fill up, the higher static compression makes up for the poor dynamic compression at part throttle and gives them better mileage and emissions, which are critical in production cars with requirements to meet in those areas. But they usually have to compromise their tune at WOT, with factory "safe" tunes often being pig rich and short on timing.
And just fyi, most new factory cars are running the 11:1 and 11.5:1 ratios for part throttle mileage. At part throttle you're starving the cylinders to breathe, so they barely fill up, the higher static compression makes up for the poor dynamic compression at part throttle and gives them better mileage and emissions, which are critical in production cars with requirements to meet in those areas. But they usually have to compromise their tune at WOT, with factory "safe" tunes often being pig rich and short on timing.
10-28-2010, 01:05 PM
#7
2nd Gear Member
Thread Starter
Join Date: Apr 2009
Location: Illinois
Posts: 422
Thanks for all the input guys.
Im probably going to pick up the motor tomorrow, how do i figure out what cam will make the best power?
Compression and cam work together. 9.5:1 can still let you run a healthy cam up to 6,500rpm easily. Also engines make quite a bit more power with more timing and less compression than they do with less timing and more compression. With more modest compression and the correct cam, you can run a more aggressive tune safely on pump fuel than you could otherwise. The extra timing will give you more power over a wider rpm range, better throttle response and better mileage.
And just fyi, most new factory cars are running the 11:1 and 11.5:1 ratios for part throttle mileage. At part throttle you're starving the cylinders to breathe, so they barely fill up, the higher static compression makes up for the poor dynamic compression at part throttle and gives them better mileage and emissions, which are critical in production cars with requirements to meet in those areas. But they usually have to compromise their tune at WOT, with factory "safe" tunes often being pig rich and short on timing.
And just fyi, most new factory cars are running the 11:1 and 11.5:1 ratios for part throttle mileage. At part throttle you're starving the cylinders to breathe, so they barely fill up, the higher static compression makes up for the poor dynamic compression at part throttle and gives them better mileage and emissions, which are critical in production cars with requirements to meet in those areas. But they usually have to compromise their tune at WOT, with factory "safe" tunes often being pig rich and short on timing.
10-28-2010, 09:36 PM
#9
Compression and cam work together. 9.5:1 can still let you run a healthy cam up to 6,500rpm easily. Also engines make quite a bit more power with more timing and less compression than they do with less timing and more compression. With more modest compression and the correct cam, you can run a more aggressive tune safely on pump fuel than you could otherwise. The extra timing will give you more power over a wider rpm range, better throttle response and better mileage.
And just fyi, most new factory cars are running the 11:1 and 11.5:1 ratios for part throttle mileage. At part throttle you're starving the cylinders to breathe, so they barely fill up, the higher static compression makes up for the poor dynamic compression at part throttle and gives them better mileage and emissions, which are critical in production cars with requirements to meet in those areas. But they usually have to compromise their tune at WOT, with factory "safe" tunes often being pig rich and short on timing.
And just fyi, most new factory cars are running the 11:1 and 11.5:1 ratios for part throttle mileage. At part throttle you're starving the cylinders to breathe, so they barely fill up, the higher static compression makes up for the poor dynamic compression at part throttle and gives them better mileage and emissions, which are critical in production cars with requirements to meet in those areas. But they usually have to compromise their tune at WOT, with factory "safe" tunes often being pig rich and short on timing.
hence the reason the factory LS series engines (which have between 10.5-11:1) use a VERY wide LSA to prevent the cylinders from filling up as well under high load/rpm situations...
