Bottom End

[ryd0rz]

Engine: 420a
Trans: Aut.

I plan on building my bottom end soon. (in approx 2 weeks). I have been running through my mind as to what I should get my compression ratio set at.

So you know my goals, I wish to be running approx 150 shot of nitrous oxide, with a turbo charger. That being said, I was wondering what you guys thought i should set my compression ratio at?

I was thinking 8.6- 8.9. Maybe you more experiance 420a builders will be able to help me make up my mind on what would be best for a turbo/nitro combo.

I plan on boring it out probably 20, because my engine is in decent shape, tell me if I'm wrong about the bore size. I would like to know if it's better to bore it out as much as possible or to leave it as close to stock as possible... I have heard that it is better to leave it as close to stock as possible (from my competition... , so i'm not sure).

and, if anyone knows a good machine shop close to indianapolis... LET ME KNOW! , i'm willing to drive... far if it's a really god-like shop

 

[VelocitàPaola]

Try posting in the 420A Bolt-On Tech forum for all of your 420A related questions; you'll get more directed and knowledgeable answers here.

8.6:1 or 8.8:1 pistons are definitely the way to go if you're boosting. It'll be extremely difficult to tune your engine for higher boost (or nitrous) using pistons with a higher compression ratio than that.

If your engine is in decent shape, you'll probably want to get 0.020" overbore pistons. How far you actually bore the cylinders out, however, depends on the piston manufacturer's recommendations. For instance, I bought 0.020" overbore pistons from JE, but they suggested that I bore my cylinders out to 0.040". Don't think about that too much though; if you just give the instructions that came with the pistons to the machinist, they'll take care of the rest...

Generally, you won't see any advantages/disadvantages by boring out the cylinders. A 0.050" overbore is generally accepted as the upper limit to cylinder boring, before structural integrity begins to be compromised. As long as you don't bore the cylinders out more than that, you'll be fine.

 

[cc8balla]

There really is no set bore to bore the block out to. Any competent shop will determine the bore.

If I were going to run your setup, I would personally run an 8:8.1 CR. Lower for ease of tuning. Stock CR is 9:6.1, so 8:8 is just fine. Most people run this CR.

 

[DSMcrazy3]

I would suggest going with the 8.6:1 pistons if you plan on boosting and spraying, but that's just me.

 

[BigRand]

If your planning on boosting and spraying, a 150 shout sounds nice, Do you know what kind of nitrous system ie a fogger system?

I think hahn used a 150shot on their 10 sec beast, so good luck.

Pick out your engine managment system carefully.