Lower compression or run stock??

[bmxdad]

This should be fun ... for those boosting ...

So, do you drop the compression losing off boost power or maintain stock compression and keeping the torque and power while off boost power.

I ask this cause I've read a few topics were the users who have dropped compression are a little disappointed on the off boost power, even while in the boosted mode.

I myself, I'm going with the stock compression and 10psi, using the secondary injector setup.

So, compression or no compression????

[BLK02XD]

I've done both ways, and dropping the compression is the way to go. our cars are tourqey enough so they aren't gutless with lower compression (8.5:1)

[Keyan]

I've spiked 14psi on a 13g with stock compression and my car still runs like brand new; and with the normal compression i get BETTER than n/a gas milage.


10psi on a t3 turbo i dont know about though.

[mayollo072R]

unless you're going over 12 psi and over 250 whp you should stay OEM. There is no need to waste a lot of gas and money on bigger injectors to run 20 psi when the result your getting is the same with OEM compression. Remember that I have a DLD, at 5psi, with 205 whp, 133k miles on the engine, never opened or repaired, running at 14.7 A/F and still have from 200 to 210 compression in each piston.

Now I want 300whp and thats why Im tunning it and if the engine needs repairs the pistons will be 10.1.

Also don't forget that our engines are 2.0l on stroke not bore. Lowering the compression with new pistons will also lower the stroke.

[Cypher]

whoa whoa whoa, lowering the compression will not affect stroke.

[BLK02XD]

unless you're going over 12 psi and over 250 whp you should stay OEM. There is no need to waste a lot of gas and money on bigger injectors
true, but if you are looking at making more than that gas and big injectors shouldn't be an issue, I would much rather have a reliable engine, than one at it's limits all the time. seems to me like forged 9.5:1pistons like labmixz had are the best option

[mayollo072R]

So if I use a OEM 7.8:1 pistons with rods kit my car will stay 2.0l?

[BLK02XD]

you'll still have to same stroke, because it's still the 2.0 crank, just the rods will be much shorter, and pistons a little taller, lowering compression. and i beleive that would actually increase the air held in the combustion chamber increasing displacement

[mayollo072R]

you'll still have to same stroke, because it's still the 2.0 crank, just the rods will be much shorter, and pistons a little taller, lowering compression. and i beleive that would actually increase the air held in the combustion chamber increasing displacement


Thanks for the clarification. Always thought that the rods have a lot to do with this.:redface:

[Cypher]

displacement will not change since displacement is a function of bore and stroke. Just the amount that you are compressing the mixture will change.

[BLK02XD]

^thats why i said i beleive, i wasn't 100% on that thanks
i don't really think the 1.8 kit is the right way to lower compression, it's cheap, but not right. forged pistons with a dish to them is the way to go.

[KeWLKaT]

Yep actually tghe formula to know the displacement is area_of_cyl*nb_of_cyls*stroke

and since the stroke is remaining the same with different rods/pistons, displacement is the same.

Now, if you have a custom CRANK, then your displacement changes.

[slow 2K2GT]

Since you arent looking for huge power then I would say remain at stock compression. If you were going to shoot for some higher numbers then maybe a set of CP pistons (8.5:1) on stock rods would be the way to go.

From personal experience the 1.8s are a reliable method of lowering compression while maintaining 'decent' DD habits, you deal with slightly lower power gains but if you want to go for those big numbers then the option is there as well. I made 205whp at 14psi from my 15t, but I am willing to bet my clutch and failed tranny had a little play in those numbers.

In the end, it costs a lot less to replace internals then it does to rebuild or replace a bottom end, take that how you will.

[BestRedRide]

If I were to lower my compression again (and I will), I'll be going with some forged 8.5:1 pistons, and a fresh cylinder rebore. I run a decompression plate right now up to 17-18 psi'ish' daily driven, 4 years, no issues with it.

-BRR

[cclngthr]

On my spare engine, which I finally built, I used 9.5:1 CR forged pistons with forged rods. Right now, the engine is n/a, but it is built for a turbo setup which I'm planning on doing. I would not go lower than 9:1 CR.

[dmdicks]

You can run the 1.8L setup but I'd recommending decking the block to gain a few precious CR points.

[Keyan]

i'm going to be the EXD guinea pig and see how much boost a stock block can run (with a correct tune mind you; i am not just going to "turn up the dial")

[KeWLKaT]

i'm going to be the EXD guinea pig and see how much boost a stock block can run (with a correct tune mind you; i am not just going to "turn up the dial")

Take care of your debt first, Keyan.

[jalmir]

didn't a guy on RDT got around 425hp before shoting a rod through the block???

[Keyan]

didn't a guy on RDT got around 425hp before shoting a rod through the block???

news to me?

[Cypher]

tim got to 408whp with just low comp pistons on the 1.8. Hes the only one that really comes to mind. Jongtr got up to 300whp with a stock motor.

[Denisst99]

dayly about 15 psi on a stock bottom end 2.0
ran a winter with crazy boost spikes (over 25 psi)
ended up with one broken piston,but i was abusing it plenty ;-)

[cclngthr]

For my engine, which will be on boost, I chose a lower CR, but not too low. I think 8.5:1 is a bit low especially at lower rpm (low boost/no boost conditions) where you want enough power to get moving. I chose 9.5:1 CR.

[jalmir]

news to me?

Can't remember the detail and I'm too lazy to search but I think that was actually stock rods, and not stock engine! sorry for the confusion!


ended up with one broken piston,but i was abusing it plenty ;-)

lol yeah I remember seeing it, missing chunk and a big crak on one side! lol