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| 2G pistons in 4g61 http://www.4g61t.org/forum/viewtopic.php?f=6&t=11352 |
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| Author: | Boostin [ Mon Oct 25, 2004 11:48 am ] |
| Post subject: | 2G pistons in 4g61 |
Not sure if I want to invest in 4g63 right now, so I was thinking about rebuilding a 4g61t that I have sitting on the shop floor. Then I got the thinking how can I make a few more ponies out of it. Bang it hit me. 2g pistons in a 4g61. Raise the compression, better turbo spool and off boost driveability. Do any of you guys know if those pistons fit in the 4g61. I t is great cause You can buy some used stock ones and they will be oversized for our engie. |
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| Author: | PatrickB [ Mon Oct 25, 2004 11:55 am ] |
| Post subject: | Re: 2G pistons in 4g61 |
Quote: Not sure if I want to invest in 4g63 right now, so I was thinking about rebuilding a 4g61t that I have sitting on the shop floor. Then I got the thinking how can I make a few more ponies out of it. Bang it hit me. 2g pistons in a 4g61. Raise the compression, better turbo spool and off boost driveability. Do any of you guys know if those pistons fit in the 4g61. I t is great cause You can buy some used stock ones and they will be oversized for our engie.
i think for the investment in taking out the motor having a machine shop fit the 2g pistons in. all the work on the block and rods u could just find a decent 4g63 and have a lot more powerful motor.
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| Author: | Boostin [ Mon Oct 25, 2004 11:58 am ] |
| Post subject: | |
Have spare motor on fn the shop floor. I work at a shop and get a deal on parts and machine work. If I go with 63, I need ecu fuel pump for sure, and the list goes on. The spare engine allready has a rebuilt head. Mike |
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| Author: | FatBastard [ Mon Oct 25, 2004 12:55 pm ] |
| Post subject: | |
It'll work, but the compression wioll actually go down. The dish of the 2G piston is meant to compress 2.0L of displacement, not the 1.7x that boring out a 4G61 to would give you. The compression ratio would drop approx a full point, to around 7.5-7.7:1. Perfect for running lots of boost! I'm doing the exact thing, except for a using a set of 9:1 forged pistons. I'm using the stock 4G61T for now, just to see how well I like it with the big turbo. |
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| Author: | Boostin [ Mon Oct 25, 2004 6:08 pm ] |
| Post subject: | |
I do not undestand how the compresseion would drop? |
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| Author: | Imon Fyre [ Mon Oct 25, 2004 8:04 pm ] |
| Post subject: | |
think of it this way.... in the g63, you have 500cc of air/fuel in the cylinder at the bottom of the stroke. when at the top of the stroke, the a/f will be compressed down to a fraction of what it was at the bottom of the stroke. this is where the compression ratio comes in. if you have the 2g 9.0 pistons that are for 2000cc of displacement, and you put them in a block that is aprox 1700cc, then the amount of a/f at the top of the stroke that is squished is going to be less. |
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| Author: | VWDSMGUY [ Mon Oct 25, 2004 9:01 pm ] |
| Post subject: | 2G pistons |
Just some thoughts-- Isn't there like 1/8'" difference in bore size. If so, that makes for a pretty thin cylinder wall. You'll notice most only go .020" over, .040" at the most. Also since the 2.0L has a longer stroke did they change the piston pin location or did they use a longer rod? You need to know the pin to piston top length to make a comparison. |
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| Author: | Skrenos [ Mon Oct 25, 2004 9:09 pm ] |
| Post subject: | |
isnt the deck height of the block like 4mm higher in the 63 compared to the 61? |
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| Author: | dragstr4g61t [ Mon Oct 25, 2004 10:02 pm ] |
| Post subject: | |
This has been covered but the rods are Identical and the block is 4 mm shorter on the 4g61t. You can bore a 4g61t beyond a 4g63t if you like, the super short stroke nets for much less force against the side walls. Also since the block is the same you could use a .040 over 4g63t piston and gain that much more displacement. You can not use a 4g63t crank...don't even think it will work, it won't. |
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| Author: | Boostin [ Mon Oct 25, 2004 10:18 pm ] |
| Post subject: | |
question is can I use 2g pistons in the block and will it raise compression? |
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| Author: | xlr8 [ Mon Oct 25, 2004 10:21 pm ] |
| Post subject: | |
That's 2 questions: 1. Yes you can use them 2. No, compression will go down not up. |
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| Author: | Boostin [ Mon Oct 25, 2004 10:26 pm ] |
| Post subject: | |
So there is no way to bump compression in a 61. So if I put 1g pistons in the engine compression would be ultra low. I still do not understand how compression will be lower. Is the wrist pin in a different location? Does the piston have less dish? |
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| Author: | BlueBullet [ Tue Oct 26, 2004 1:45 am ] |
| Post subject: | |
actually....the funny part is that a 61t has 1st gen rods and pistons. Its the crank that sets them apart. The crank has a shorter throw, which makes up for the short deck hight. The displacement between the 61, 63 and 64 is only deck hight difference. That and I think the 64 might use a longer rod but i could be wrong. I have spec sheets somewhere around the house with all that on it. I have to find it... |
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| Author: | xlr8 [ Tue Oct 26, 2004 3:08 am ] |
| Post subject: | |
Static CR is calculated as such: CR = Volume of 1 Cylinder / Compressed volume of 1 cylinder When you change from a 4G63 2.0L with a 88mm crank to a 4G61 with a 75mm crank (and a 6.5mm shorter deck height) the swept volume of 1 cylinder goes down from ~500cc to ~400cc. Given your using pistons with the same shaped crowns the compressed volume remains the same in either motor which means that the static CR must go down because your now compressing less gas to start with! For example consider 2G pistons in a 4G63 block: Piston OD = 85.0mm = 0.850m Stroke = 88.0mm = 0.880m Swept volume = 499cc = 0.499L (4G63 2.0L = 1996cc) Combustion Chamber Volume = 43cc Piston Dish Volume = 17cc (std 4G63 Wiseco 8.3:1 piston) Combustion Volume = 43 + 17 = 60cc CR = 499/60 = 8.3:1 CR Now the example of the 4G61 block with 4G63 pistons: Piston OD = 85.0mm = 0.850m Stroke = 75.0mm = 0.750m Swept volume = 425.6cc = 0.4256L (4G61w/85mm pistons 1.702L = 1702cc) Combustion Chamber Volume = 43cc Piston Dish Volume = 17cc (std 4G63 Wiseco 8.3:1 piston) Combustion Volume = 43 + 17 = 60cc CR = 425.6/60 = 7.09:1 CR If you wanted to maintain CR in this instance at 8.3:1 with the 4G61 you would need to use the same pistons except with a ~8cc dish instead of a 17cc dish. The maths doesn't lie. |
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| Author: | PatrickB [ Tue Oct 26, 2004 7:13 am ] |
| Post subject: | |
u want to bump compression up some ? deck the head and block. if u want turbo to spool faster switch over to 63 cams on the exhuast side and port the exhuast ports and manifold. if had a machine shop at my disposel I would just port everything. i can't say i know a lot about the 4g61. can u use the 1g intake manifold w/ the big throttle body? that would help some if you could. |
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