nick6444

Heres what Im gettn ready to buy. I have a h22a4 and for pistons I am looking at: http://cgi.ebay.com/ebaymotors/Honda...ht_3374wt_1352 And for rods im looking at: http://cgi.ebay.com/ebaymotors/Eagle...ht_3080wt_1184 Im just a little bit baffled to what size pistons bore wise to get, keeping in mind that i have stock bore. And also what cc dish to get.

Jas9848

iTrader: (2)

depends on what compression you want

nick6444

What compression is ideal?

LastGenEK

If you plan to build this engine yourself you better do your reading before you start to buy stuff...

With my build i went with as low comp as possible... because i knew i would be driving the car everyday and i wanted it to be reliable

I figured when im not boosting The low compression would be easy on the bearings and sleeves

92civiceg9gsr

10.0-1 is a little on the high side for a boosted motor. 9.0-1 to 9.5-1 would be more ideal imo.

nick6444

What is the disadvantage of lower compression? Loss of potential power?

blinx9900

I have 8.3 CR, off boost driving is a bit sluggish, fuel economy is kinda poor but its all minor imo, i have driven high CR boosted setups also, the difference is not as HUGE as people think...

srmofo

I had a 8.5 boosted LS and the thing was a dog when it wasnt in boost. After that though you couldnt tell a bit of difference.

HiProfile

I'm so surprised you guys use your *** dyno for something like that - the same guys who'll kick & shout when someone claims thier FMU/V-AFC tuned ebay turbo kit rips vtak harder than their bro's nawz kit. Granted its very uncommon to change just compression, you're still offering personal experience based on only one view point with proof being your buttdyno.

Jeff Evans proved that 10ish:1 vs 9:1 gives almost no difference in power (and zero difference concerning spool-up). They took a stock-block turbo setup, simply swapped out the bottom-end for a 1-point lower CR built shortblock, and the NA portion of the map had virtually zero change. Boost made a little more power per PSI with higher CR, but before full boost the lines touched.



To make a long story short, 10:1 will be less 'safe', and will limit your max boost level (due to higher peak cyl pressure) a bit more than 9:1 or 8:1. But if you don't plan on upgrading your MAP sensor to go over 10psi, its no problem unless you use a crazy turbo like a GT45. If you look around, most built motors people here have are ~9:1 CR.

TheShodan

iTrader: (14)

This is where Jeff Evans and I tend to agree on this aspect, but differ in our point of view. Of COURSE top end power is not going to change b/w 8.5, 9.1 and 10.0:1 compression, because of two reasons: 1) When one reaches a particular power level, the effective compression is going to stay the same regardless of static compression level. i.e. if the effective compression that an engine reaches in boost is over 18.0:1 (which surrounds the entire reason for going into "boost"), it wouldn't matter if the static compression was low or not, since given a particular turbocharger, it will reach that level of effective compression eventually, and 2)the effectiveness of the slightly higher compression has nothing to do with the car being in positive pressure, but how it operates OUTSIDE of that pressure level when the car is going in between shifts or generating enough exhaust energy to build boost. This is the reason why srmofo had such a dog time at 8.5:1 as a static compression, until the turbo helped the engine reach his maximum effective compression for a longer duration of time. He was so far off of his effective compression with the turbocharger used, that the car lagged like crazy.

It is important to understand the "higher static compression for boost" argument that myself.Tony the Tiger, and others have been advocating on the forum for years; it looks more at the quicker gain to the effective compression that a turbocharger reaches from one point to the other. (meaning, it takes longer to get to 17.0:1 as an effective compression w/ 8.5:1 static compression, then, say with 10.0:1 static compression.). the slightly higher static compression also helps with acceleration rate of the car since it is able to reach its effective compression more easily with a shorter duration of time. Just like in an N/A car, or one that is supercharged.

10.0:1 is no less safe than if it was 9.0:1. It depends upon the tuner, the tune, and the fuel grades available in your area.

blinx9900

HiProfile I never said there was a power difference in low compression vs high compression boosted setups, i simply stated off boost driving is a bit sluggish with the lower CR.

srmofo what tranny did you have? My b16 gearing helped the slugishness feel almost non existant and it only really became apparent if i had just driven someone elses car.

srmofo

I had an ls trans in at first, but later I switched to an 98 ITR and it helped tremendously

TheShodan

iTrader: (14)

In your case, srmofo, the change in final drive and 3rd gear also assisted in keeping the car in tighter powerband which helps your ultra-low compression honda gain a bit more acceleration.

blinx9900

yup, i always thought the same of my setup, my b16 gearing really helps make up for the low CR when im driving on the motor...

HiProfile

The easiest way to draw a conclusion is to break down how each 'method' makes more power.

*High Compression: forces the atoms closer, which burns them quicker. That enables a higher percentage of power nearer to TDC. Similar to how a higher rod/stroke ratio works.

*Increased Boost: forces the atoms closer by stuffing more in. It enables more power to be exerted at every crank angle, aka higher average cylinder pressure.


An example would be 2 bone-stock motors, exactly the same except one is a 13:1 CR all-motor, the other has a VERY BASIC turbo kit @6psi (13:1 effective CR). Will the extra low-end torque really matter? Only if you like to race from idle to 3k; know anyone who does that? This is an extreme example, but the main difference is average cylinder pressure due to extra burnable mass "force inducted".



How often will someone lug a 4-cyl? I don't know about your guys' daily drivers, but my 8:1CR D16Z6 is more than enough out of boost, even in a full-weight '95 EX with a DX trans. I rarely lug it by accident in town. FYI burning a fuel mixture quicker (higher CR) doesn't create more exhaust energy. You're still burning X amout of oxygen atoms, and exhausting the same Y amount of gasious mass.