Increase comp ratio on 455

[Guest]

Can a 1975 455 engine be <BR>modified to regain the compression ratios produced <BR>on the earlier (1970 or so)<BR>pre pollution control engines<BR>Whats involved? Changing the<BR>heads?, pistons?,etc?<BR>Is this worth doing for added<BR>HP? Also would exhaust and intake mods be necessary?<BR>Can't remove the cat converter do to emission<BR>inspection requirements. Any<BR>info on this project would be<BR>helpfull.

[Guest]

If the car is going to be inspected for emissions then it won't pass the smog check with higher compression. <BR>The compression can be changed by changing the pistons. For more performance the heads can be machined for larger valves.<BR>Depending on how you drive the car is the deciding factor on wether it is worth it to raise the compression. I'm running 8.5:1 compression on my 71 Riviera and it is a good daily driver that runs on 87 octane gas while still producing 320 horsepower and stump pulling torque. The camshaft is an after market level 2 cam which really woke up the engine. I am happy with it, but I can only school Civic and Celicas at stop lights. If you aren't driving the car often then I would recommend raising the compression because it is an easy way to make insane power with this engine. Car Craft just did a build up of a 555hp 455 Buick.

[Guest]

Joe,<BR> If you are going to rebuild the engine it pays to increase the compression. The 1975 heads were open chamber type heads and the pistons had a deeper dish to them. You can get high compression pistons (10.2:1)and run a 0 deck height to bring up the compression. You can also switch over to 70-73 heads which have smaller combustion chambers for more compression. A good machine shop can set the engine up and measure your true CR. If you want the motor to run on pump premium you'll want to limit the CR to 9.5:1- 10:1. If you use all three above suggestions you could end up with over 11:1 and then you would need race gas. Compression enhances horsepower and torque, it is an important variable in any engine rebuild. Just put the motor in an older car and you won't need to worry about emmissions testing. You'll need a good free flowing dual exhaust of 2 1/2" minumum. Use an Edelbrock performer manifold with a rejetted quadrajet. And lastly pick a cam that matches the way you intend to use the engine (most important) TA performance has some great cams. 480-922-6807 Built right, the buick 455 will scare you. Good Luck.<BR> Larry<p>[ 01-06-2002: Message edited by: Larry Hymowitz ]