piston compression ratio

[an orange crayon]

what is the difference bewteen 8.5 to 1 and 9 to 1 i know its higher compresion but what will the difference in the end result be?

 

[bryanwheat]

The difference is the dish in the top of the piston. The 9.0:1 will have less dish than the 8.5:1. This will make more pressure in the cylinder when the piston is at tdc. The result will be slightly better throttle response off boost, slightly better spool, and a little more power with less airflow. There are drawbacks to higher compression though. You will have to reduce your timing under a load to cut back the chance of detonation, and you will be able to make less power on lower octane fuel.

 

[97gst5887]

So it's more street able if your running a bigger turbo on a good tune right?

 

[bryanwheat]

Realistically you probably won't even notice the difference. You would probably see it on a dyno, but likely not notice that much of a difference.

 

[an orange crayon]

ok so really no big differance but on an everday car probably 8.5 to 1 would be the better choice?

 

[NHerron]

I choose 8.8:1. I sometimes wonder if I should have gone with 9:1 instead for better off boost performance. But I haven't gotten far in tuning yet so I can't say I wish I went with 9:1 yet. Bryan pretty much nailed it, per the usual.

But definitely search more before you make a choice

 

[My1GLaser]

ok so really no big differance but on an everday car probably 8.5 to 1 would be the better choice?

It depends on what you're tuning with. If you have timing control then I say go with 9:1. I ran that CR on pump for years with no tuning issues. I ran 18* timing and upwards of 26+ psi.

Keep your coolant & intake temps as low as possible. Run colder plugs. Try non-projected plugs if necessary. Make sure the combustion chamber is polished and there are no sharp edges. Try to get your piston to head measurement to be around .040" (quench area). The thickness HG you choose & where the pistons sit relative to the top of the block affect that measurement.

 

[an orange crayon]

It depends on what you're tuning with. If you have timing control then I say go with 9:1. I ran that CR on pump for years with no tuning issues. I ran 18* timing and upwards of 26+ psi. Keep your coolant & intake temps as low as possible. Run colder plugs. Try non-projected plugs if necessary. Make sure the combustion chamber is polished and there are no sharp edges.

what do you mean by timing control? i dont tune yet at all

 

[My1GLaser]

what do you mean by timing control? i dont tune yet at all

The 1G timing curve is VERY aggressive from 5500-6500 rpms. It shoots for 22* @ 5.5k & 24* at 6k. That's way too much timing for pump, 9:1 CR and/or high boost.

You are going to need DSMLink or something that will allow you to change the timing settings in the ECU if you are going to venture too far away from stock CR & boost levels.

 

[an orange crayon]

The 1G timing curve is VERY aggressive from 5500-6500 rpms. It shoots for 22* @ 5.5k & 24* at 6k. That's way too much timing for pump, 9:1 CR and/or high boost.

You are going to need DSMLink or something that will allow you to change the timing settings in the ECU if you are going to venture too far away from stock CR & boost levels.

so then if im not going to get a link anytime soon i should just go with the 8.5 to 1 then?

 

[My1GLaser]

I just saw your other thread about the pistons. What boost do you plan on running on the 14b?

 

[an orange crayon]

what turbo & boost?

ill be running a 14b i dont know how much boost dont have my car built yet just working on building my bottom end

 

[talonESturbo]

go with the 9.0.1 cr and run e85 an turn the boost uuupppp