IS HIGHER COMPRESSION BETTER???

[tristan rizzi]

I have a TNT 555 package on my 94 viper w/ 655 heads, and am getting ready to balance and blueprint it. Since I will have the motor apart I was wondering what kind of performance benetits I would get from raising the compression to the 10.5 -10.7 :1 region. Will the stock computer adapt to this configuration??? Since I am changing the pistons should I have the sleeves bored, and if so how much. Thanks for any advice offered.
Tristan

 

[treynor]

Since you're in Florida, are planning on opening up the engine and changing pistons anyway, and clearly want more power, why don't you bring the car over to Doug Levin and have him discuss *ahem* your performance requirements with you. You'll get fairly marginal gains from just bumping compression, and you'll risk detonation (Vipers have no knock sensor). *Lowering* compression and pushing more air in might be a much better solution

 

[Marv S]

good luck running 92 ron/mon. You don't have a knock sensor to back off the timing and some of the snakes are borderline at stock gen2 9.6 when running hot. You can get by with a bit of mill, but 10.7 may not be all that durable.

CA lowered to top octane to 91 at sea level now. (except for $$$ unleaded race gas at some places)

 

[TOOOFST]

$ for $ Nitrous will give the feel and when the challenge comes,you'll agree its the best spent 2-3g's yet on the car!It'll clean your motor and loves low compression.

 

[ntmatter]

So, can I expose my ignorance here and ask for a brief tutorial on engine compression as it relates to Vipers? How does adjusting compression get done, and why is it good / bad. What do we mean by lowering compression and adding more air? What does the compression ratio mean? A few paragraphs on the fundamentals would be appreciated.

 

[TOOOFST]

Fred,If you live in warm weather and don't have a warranty,and wanna run 11's,with $20g lying around,turbo's,superchargers are the answer.Most guys can't keep the stock car on the ground.Do you think adding 100-150hp to the motor(all the time) might shorten the life of stock motor?There's a sacrifice for every situaion.For cars that are stock with warranty there's no better way.I can go to the track and pop in a ******(Nitrous jet,same diff.)and kick a$$,purge at the line and have the crowd cheering.Using $1000.+- of nitrous is enough to keep respect,make a show all year,without beating up your gas tank.A few extra plug,oil changes, whatever.

 

[ntmatter]

Thanks for the reply, I understood everything up to the last sentence. If we shave material off of the head of the top of the block, wouldn't we be creating more space, and thus lower compression? I understand that a domed cylinder would take up space in the compression chamber ordinarily occupied by air, but how does removing material create less space? (I assume this is what a "ported head" is?).

Also, is there a "best-known-good" mod for Viper compression that optimizes the car's use on street gas (91-92 Octane)? I'd expect that this would be the default setting, and I rarely hear about a piston swap that would boost power, compared to adding N2O or a turbo, so I assume not.

Thanks,

A.

 

[Marv S]

Andy, Glad to read that they caught the guy who stole your rims. Porting increases the cfm (volume) of air that will travel through the head and milling-decking etc. raises the compression. As for milling the head, picture this: Turn the head upside down and measure how much water will fill one chamber, valves closed of course. Let's use 67cc as an arbitrary number. now mill, deck, shave, etc the head and the chamber will be shallower. This will result in the chamber holding less water because the volume of has been decreased. Less volume results in more "net squish" or compression of the air. This is a bit simplified as there are several other issues to consider when milling-decking, especially depending on if the motor is ohv or ohc when valve timing is effected but another time.. Also, I think it's "domed piston" rather than domed cylinder. <BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by ntmatter:
If we shave material off of the head of the top of the block, wouldn't we be creating more space, and thus lower compression? I understand that a domed cylinder would take up space in the compression chamber ordinarily occupied by air, but how does removing material create less space? <HR></BLOCKQUOTE>

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by ntmatter:
(I assume this is what a "ported head" is?). <HR></BLOCKQUOTE>

Ported is when you open up the area between the valve and where the intake or exhaust manifolds connect to the head to get more volume (CFM) of air into the cylinder.

 

[tristan rizzi]

Thanks for all the replies,
There is certainly a lot to consider.

Tristan