Small Question (Rebore)

niky · Jul 20th, 2002, 04:31 AM

I just recently totalled my engine, a GA16DE, on my 2 year-old automatic Sentra. I brought it to a machine shop, and they are charging me an arm and a leg for the thing. One good thing is, I'm getting my pistons re-sized and my exhaust ports polished off... (well, that's two, then...).

Here's the question, though... would any of you know how much of a displacement change it will be when we re-bore a 1595cc engine out around 0.50"? Would I need to have my ECU and/or fuel system re-worked to take advantage of this?

bahearn · Jul 22nd, 2002, 11:20 AM

Simple math will determine the capacity.

First find the bore and stroke of the stock GA16.

Capacity = ð [pi] r squared h * 4 where pi ~ 3.141592, r = radius [1/2 bore], h = stroke and 4 = number of cylinders.

To find the new capacity, add 0.5" (really? 0.5 inches?!) to the bore, divide by 2, square it, multiply by pi and multiply by the stroke, finally, multiply by four. Don't forget to use matching terms (don't mix metric and "standard" units).

pi*((bore+overbore)/2)squared*h*4

Be aware that the compression will change (probably go up) but that is quite a bit more complicated formula and requires knowing the combustion chamber volume in the head.

James · Jul 22nd, 2002, 11:37 AM

Dude you aren't gonna get a half inch out of there... I've read and been told 2 thou at most. Do some searching, you'll find some interesting reading.

SE-R Kid · Jul 22nd, 2002, 01:36 PM

If it's a rebuild rebore, with the stock pistons, a machine shop MIGHT make the stock pistons work in a .0050" overbore situation... which is almost nothing, just enough to get rid of the factory cross hatching.

You won't get any extra horsies from overboring... Sorry.

The tiny amount that an overbore adds to the displacement is negligable.

bahearn · Jul 22nd, 2002, 02:27 PM

I don't know the bore of a GA16, but the bore of an SR20 = 8.6 cm and its stroke is also 8.6 cm for a capacity of 1998 cc. 0.020 in is the maximum allowed overbore for an SR20. 0.020 in = .051 cm.

((8.6+.051)/2)^2 * 3.141592 * 8.6 * 4 = 2022 cc. This is a 1.2% gain in capacity. It should generate 1% more horsepower; 140 (stock hp) * 1.01 = 141.68 hp.

Or, 140 horsepower / 1.998 liter = 70.07 hp/l
70.07 * 2.022 = 141.68 hp.

I would hazard an equivalent gain in power for the GA16 at .020" over, that is, expect maybe 1% gain over stock, all else being equal.

ANYTHING that moves more air through an engine will cause a power output increase, including even incremental gains in capacity.

niky · Jul 27th, 2002, 02:25 AM

well, okay, so maybe it's 0.050. I'm not really much up on the technical bull, i just drive the thing...

...but it's really hard to find out. i just went back to the shop friday, and they'd finished my block. The rebore didn't look too radical, and there was lots of sleeve left. I'm vaguely disappointed.

But i know i'm not getting stock sized pistons. The machine shop i'm using is very particular about fit, and they're taking so damn long because they are rejecting almost good replacement parts left and right!

i'm going to check again, though. some dude on another site... (fergot the damn url!!!) ...claims he got his engine up to 1.635 out of a 0.040 rebore and is running it on an SR20 fuel system. Says he's kicking ass with it at rallycross, i think. I just wanted to know if the same would work for me.

Well, if anything, at least i'm getting an exhaust port job out of this, and if bahearns' calculations fit, i'm getting

2 more horses out of this thing... but the exhaust port work should give me another 2 to 3. Anyway, i'm having headers put in right after, and i'm going to find the most inocuous, innocent sounding, low-restriction muffler i can find.

Air filter will probably stay stock, with a different hose on the end to prevent the same thing from happening to my re-worked engine. Picture this: My sentra sucked water up through the bumper extension of the air filter! And that filter is completely stock! (bonehead me, i was driving the ONE car we had that DIDN'T have a custom filter...)

hopefully, ma won't kill me when i drive her to work the next week.

thanks for taking the time to do my math!

LexKyB13 · Jul 28th, 2002, 08:44 PM

FYI, the bore on the ga is 2.99, and the stroke is 3.46.

CarbonBlack200 · Jul 28th, 2002, 09:50 PM

niky lives in Phillipines right? I think 0.5" means 0.5mm oversized piston. We use metric system in Japan. I believe phillipine is the same way too. If the piston is 0.5mm wider, compression will go up a little bit. Not much though.. I don't think it will go that much higher, but you might wanna keep your eyes open for knocking/pinging. If possible to get high octane gas there (i don't know about octane rating in Phillipines), do so.

niky · Jul 30th, 2002, 01:13 AM

i am going back to the shop this week. I will probably know by tomorrow what the actual size is. The machine shop and mechanic both say that my gas bill is bound to go up quite a notch. Too bad i can't get a higher octane gas, as the unleaded here only goes up to 93oct... but then again, that's pretty high, isn't it?

We actually DO use the metric system (officially), but since this country was a former American colony, most people still use the English values.

CarbonBlack200 · Jul 30th, 2002, 01:16 AM

We get crappy gas here in United States too. Our High Octane means 91. (some lucky people get 93). That's like regular gas in Japan. In Japan, high octane means 100.

Yeah, if you can get 93 octane gas, you should have no problem.

bahearn · Jul 30th, 2002, 10:57 AM

niky, why does your mechanic think your gas bill will increase? The (slightly) higher compression ratio will (slightly) increase engine efficiency while the (slightly) larger capacity will make (slightly) more power for a given throttle setting, allowing you to use (slightly) less throttle to maintain a given speed, ergo your gasoline bill should remain approximately the same.

LexKyB13 · Jul 30th, 2002, 03:51 PM

thats (slightly) confusing!

niky · Aug 2nd, 2002, 01:52 AM

Actually, the gas bill WILL go up slightly, as you WILL be burning more gas in idle (as long as it is not reset). Besides, the economy gained from lower revs at speed won't matter as much, since i'm running a 4speed automatic that chews up gas like hell in any event.

The rebore is the supposed maximum, at 0.5 mm. But I've found out that info i've seen elsewhere is also correct, because you can go hardcore and do a 1 mm rebore, and the pistons are commercially available! The bore doesn't sound correct in LexKyB13's message, as it makes it around 79mm, whereas I'm already using 84.5mm pistons, so by formula:

Quote:

Capacity = ð [pi] r squared h * 4 where pi ~ 3.141592, r = radius [1/2 bore], h = stroke and 4 = number of cylinders.

(thanks, dude!)

Stock:
3.1416 (42sq) 72 * 4 = 1596.03332 cc

(i'm guessing 72 as the stroke in mm, as it makes the calculations fit factory specs exactly!)

0.5 mm Rebore:
3.1416 (42.25sq) 72 * 4 = 1615.09028 cc

1 mm Rebore:
3.1416 (42.5sq) 72 * 4 = 1634.26032 cc

Now, the factory quoted bhp of the ECCS Equipped GA16DE is 116, while the SR20DE is around 145. If you go by HP per liter, the GA gets 72.5 HP (approx- 72.727272 to be exact) per liter, while the SR gets 72.5 HP also. Hoping this applies evenly across the range:

0.5 mm Rebore:
1.615 * 72.7272... = 117.5 hp (my car)

1 mm Rebore:
1.634 * 72.7272... = 118.8 hp (maximum)

But I am also getting an exhaust port polishing as part of the package, so that should ideally give me about 3hp or so more beyond that, maybe 5 or so after I change my headers. I am going to do some exhaust work after we get the car shaken in, maybe get crank HP up to 125 or more, but for the meantime, I will be happy just to get it back!

If this machine shop got my engine right, I'm going to have them do my other Sentra, a 1.3 liter manual. It's a GA13, but the block is exactly the same size and weight as the GA16, and the equipment (dual cam, 16 valve, chain timing) is almost exactly the same, except it's carbuerated. This probably means I can get away with reboring it to 85mm. And it'll cost me 272$, or 13600php. Woohoo! That's a gain of 24hp (from 95 to 118) for less than 300$!

niky · Aug 2nd, 2002, 02:07 AM

the other car is a 2000 B15 or B14, GA13, air-conditioned, no radio, and the only thing powered on it is the steering. It cost us 7000$ brand new. Basically bought it off a raffle winner who didn't really want the car. Their loss. When I get it fixed up, it is going to be pretty....

niky · Aug 18th, 2002, 11:29 AM

i finally checked the manual, and it DOES say that the bore is 2.99 or around 76 mm. I don't know why they are telling me the pistons are around 84! The revised calculations show:

3.1416 (38 sq) 87.884 * 4 = 1594.73cc
quoted as 116hp: 72.74 per liter

rebored at 0.5mm:

3.1416 (38.25sq) 87.884 * 4 = 1615.79cc
should be 117.53

sorry for being an ass and taking up column space and posting 3 in a row, but i don't want to be known as a TOTAL boob.

car's out of the shop and running fine. Haven't been able to max it out yet, still getting rid of the little niggles and odd noises that a car accumulates after being garaged and in pieces for two weeks. Engine seems noisier up front, and pulls pretty well... (if it isn't stronger, at least it's still as powerful as it was!) Had intake changed, because i put in a new battery that mashes the old filter tube. Getting headers this week. Still trying to finance that torque converter, though!

bit of good news: raced a 2.0 mazda 626 the other night. Musta pissed the guy off because he couldn't build up a lead over my little auto...