I'm thinking about getting high comp pistons.

Anyone know how high i can go on the stock rods?

 

compression from NA wont hurt rods at all, especially since a turbo can create over 25:1 elastic compression

rpms and overall power is what kills them

 

I believe the L15A7 engine is already 10.4:1, How much higher do you plan to go?

 

I'm curious what type of gains would be seen with a Stock Sized High Comp Piston (73mm, GE8)? Have you looked into what the gains maybe?

~11:1 is probably the highest you want to go. You will have to run premium from then on, something to consider. Race fuel will be required if you go any higher than 12ish. I would love to see someone do this. For a while I was throwing around the idea of a 75-85mm +/- high comp with a cam.

 

Good point! Noted.

At least 11:1.

 

In theory, about 7-8hp per point increase in CR. But, as you mentioned, better fuel is required (Suzuki's SX4 has a CR of 11:1, minimum is 95ron).

I'm thinking maybe 11 or 11.5:1. But i don't plan on changing the cam; car's got to stay a daily driver.

 

you cannot put a horsepower/torque increase related to compression.

Chamber design, ignition quality, and fuel quality are the 3 important players in whether you get measurable power increase or not.

However, I do think our motors would love 11.0-11.3 :1 even on the stock ecu.

 

^^ That can be said for any mod. Companies that sell hp related aftermarket parts do rate parts. What those companies don't tell you is they tuned the car or have supporting mods to make the max gains.

I understand what you are saying though, its more than the pistons making the power increase. It's the package. There is a lot to consider. That being said 1 point is usually a 3% gain with supporting mods. Obviously dependent on current setup. I see a cam being a must to pair with HCP.


I was curious if he saw someone do this mod and saw results.

 

Interesting mention the HPD L15A7 I believe is 115 whp with a 10.55 compression per SCCA.

 

increasing compression effectively makes your exhaust cam profile "appear" bigger to the motor, from the extra pressure and heat.

They probably bumped it up a bit to imrove the quench though.

Remember guys, Honda is pretty thorough with their motors. None of their motors really see much benefit from boltons without tuning being done.

Even on the K series, you are looking at around 25-30whp increased at most without digging into the ecu tuning. And those motors have turned out to be very efficient, regardless of their purpose for performance.

Then again, a high performance 4 cylinder is already a very efficient motor when you are breaking out crank power a mear tenth of the CC's (200hp for 2000ccs, example)

 

Have you found a set of pistons that interested you? If so where?

 

Yup. Wiseco.

 

Agreed! I think this is one of the parts where Honda held back, 'coz they wanted the Fit to run reliably on 87 octane. Like they did with the spark plugs.

 

I got a bad case of "compression-ratio-envy."

Imagine you're at the pumps filling up w/ premium.

A stranger walks up to you and says, "watcha doin fillin' up a fit with premium? Dontcha know itcha waste of $$'s?! Ya' stupid $#*!"

"See, I got me onna dem propa japnese $@&*! It got 11:1 kempressien!"

I'd feel useless, and empty, and life would lose all meaning.

(It could happen!)

 

You will not gain much from compression, especially such a small bump of <1pt static.

Add to that, diminishing returns the higher you go, assuming you were not fuel limited. If you aren't planning to run alcohol as a primary fuel, you should leave it. The $/HP is one of the worst you'll find.

What would you be tuning with anyways, a piggyback like Dastek? AEM? Greddy?

You'll wind up spending an easy $2k before getting on a dyno, spend several hundred more there and maybe pick up 3-5whp on an engine originally making ~95whp on its best day if you plan to stick with pump gas on a warm humid island that gets mediocre fuel.

Static Compression ratio means very little by its self anyways. Consider also, on 93oct (AKI, not RON) with 50*IATs our engines will see knock counts.

 

Ah, i see! Thanks professor! May i call you professor? For i learn much from your posts.

No wonder wiseco didn't have a product in their catalog that raised CR for the Fit.

Got a dastek piggyback last Christmas.

I will simply have to feel useless, and empty, and life would lose all meaning should that dreaded day come.

 

I have no doubt that Ron Shearer @ Wiseco (their Sport Compact piston guy) could have any style of slugs that will fit within the chamber geometry constraints of our little hamster mills made custom for you.

But really, unless you are running a setup intended to absolutely maximize power in NA form .. the results will be disappointing and prohibitively expensive.

If it makes you feel any better - we have variable dynamic compression ratio (VTEC) and it's kept quite high under all conditions.

 

Yes, that does make me feel better! Thanks again!

 

I already run 93, so why not push the envelope a little bit. I eventually want to see if this block can safely run 75mm pistons, and even if I keep the stock dish, Ill see a slight compression bump. Combine that with maybe flat valves, I wonder if 1.5 points is possible without slicing the head or changing the piston profile/design

EDIT I say 75mm because on my first attempt at an all motor d15, I punched it out to 77mm (stock 75mm) with custom set of Arias slugs, and the sleeve cracked after a few thousand miles of track abuse after the first 2500 miles of city driving to really break the motor in and get a really solid baseline on the motor. Pulling the head off that revealed a nice even carbon coat (ran it rich, leaned it out, ran it rich, leaned out, then final tune) and a few very small vertical fractures about a third the way down the cylinder. the pistons were fine, sold those for about 60% of their cost, so it wasnt a huge waste. PG6 pistons on fresh stock size sleeves ended up working awesome

 

It's your money. I think we are discussing a couple different things here though, the OP and myself are talking strictly about compression ratios.

With such a small engine in the first place (L15A1 - 73mm B x 89.4mm S) performing a 2mm overbore is only accomplishing a couple things:

1.) Ensuring you don't have enough cylinder wall/lining to perform a simple rebuild if you suffer FOD or a cracked ring land that could have otherwise just been punched out ~0.5mm and cleaned up.
2.) Reducing block rigidity
3.) Allowing more heat to escape to the oil and coolant circuits

2mm Overbore gets you ~80cc, doesn't feel worth it to me.

I also run 93, and have logged not just knock retard but actual knock counts at stock compression.

The L15A1/7 have pentroof chambers, so you have ways of getting greater static CR. I'll leave you with this:
Standards and Service Limits - 37