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PostPosted: Sat Jun 17, 2006 1:29 am 
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I have a set of vitara pistons here with the part number 71C50 stamped on top. What is the difference between this and 71C51 and 71820 ???

The label says 71C50 Swift 1.6. I have also found some confusing information on the web regarding the difference betweeen G16A/B and 71C50/51/71820. From various manufacturers, they seem to be the same piston, but why the different labeling ?

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Last edited by Caaarlo on Tue Jun 20, 2006 1:34 pm, edited 4 times in total.

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PostPosted: Sat Jun 17, 2006 8:26 pm 
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Caaarlo,

The Vitara pistons are offered in 2v and 4v designs. Grab the later 4v ones.

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PostPosted: Sun Jun 18, 2006 3:04 am 
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Liam,

You really think I am that dumb ? :D Both the 71C50 and 71C51 are 4V pistons and look like the same.

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PostPosted: Sun Jun 18, 2006 8:53 am 
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Caaarlo wrote:
Liam,

You really think I am that dumb ? :D Both the 71C50 and 71C51 are 4V pistons and look like the same.

thats interesting

I wonder if i can find the pics of what i had put in my engine

Caaarlo where do you see these numbers at the top of the piston?

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PostPosted: Sun Jun 18, 2006 12:05 pm 
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Yeah, my taiwanese pistons have that number at the top, but it is actually a SGP part number.

So, there are two SGP part numbers:

12111-71C50 (the ones I have)
12111-71C51

Here are some specs:

71C50: http://www.arcomotor.com/products/produ ... &twoId=510

71C51: http://www.arcomotor.com/products/produ ... &twoId=510

So far, I can only see a slightly different compression height, one is 28.3-6.1 and the other is 28.3-6.0, which is 0.1mm difference in dish depth.

GtiT, here is your piston, it's the same piston I have with 71C50 on top:

Image

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Last edited by Caaarlo on Sun Jun 18, 2006 6:58 pm, edited 2 times in total.

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PostPosted: Sun Jun 18, 2006 5:40 pm 
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Well, I have found a different piston, even though it is also a vitara one. This piston has a less deep dish than mine. See the valve cuts ? In my piston, the dish goes deeper than the cuts (6 millimeters), but in the other piston, the dish is leveled right with the valve cuts (arounr 4 millimeters), so similar pistons will lead to different compression ratios. I have calculated mines to give 7.5:1, while many people say the vitara's are 8.5:1

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Last edited by Caaarlo on Sun Jun 18, 2006 6:57 pm, edited 2 times in total.

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PostPosted: Sun Jun 18, 2006 6:38 pm 
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If the pics are accurate then it looks like the valve cut outs are in different places,
and maybe even different dishes? :roll:
Image Image


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PostPosted: Sun Jun 18, 2006 6:50 pm 
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Looks like the valve cuts are in the same place (Drawings might be a bit off). The dish looks certainly different.

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PostPosted: Mon Jun 19, 2006 8:44 am 
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whoa so thats how low my CR is ....!

thanks for the calculation caarlo
this is really an interesting topic .... this can really affect people using the vitara pistons.

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PostPosted: Mon Jun 19, 2006 10:04 am 
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No problem.
I kept searching and also found that Sebaszz has two pictures of the block with the two types of Vitara pistons :shock: , so I bet he later swapped them due to the low CR. Still, I don't know why the difference and how to order the correct ones (smaller dish).

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PostPosted: Mon Jun 19, 2006 11:09 am 
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Ok, I found the correct ones:

http://www.arcomotor.com/products/produ ... &twoId=510

Part No. 12111-71820 for the set of piston+pin

It has a 4mm deep dish vs. 6mm for the others. Either way, it lowers compression ratio a lot. still around 7.9:1 for the 71820 and 7.3:1 for the 71C50/51

Here is a drawing of the piston:

Image

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PostPosted: Mon Jun 19, 2006 11:24 am 
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So the one type of vitara pistons that I seem to see on a lot of setups are lowering compression to 7.5:1 not 8.5:1?
I'm sure the pistons I have are the lower dish ones which I had from Suzisport a couple of years ago or more. I asked them what compression ratio they would give and they said around 8.5:1.

Would you be able to explain your calculations further Caaarlo? I'm interested to find out about these different pistons.

Thanks
Phil


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PostPosted: Mon Jun 19, 2006 12:07 pm 
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It is an approximate calculation.

Here we go:

I assume the valve cut-outs to have the same volume for std G13B piston and Vitara ones. This is not true, the vitara's are larger, but let's keep things simple. Their difference is not significant in the final result. It even might be compensated by the cutout/dish overlap.


1-Stock G13B chamber volume:

CR = 10 = ( Cyl volume + Vc)/Vc

10 x Vc = 324.7 + Vc

(10 x Vc) - Vc = 324.7

9 x Vc = 324.7

Vc = 324.7 / 9 = 36.077 cc = G13B CHAMBER VOLUME

When fitting the deeper 71C50/51 piston, there is more chamber volume, because a)compression height is lower ... b) the dish.


2-Volume added by the lower compression height:

Stock compression height: 29.1mm
71C50/51 compression height: 28.4mm
Difference : 29.1-28.4 = 0.7mm = 0.07cm

Radius of piston = 75mm/2 = 37.5mm = 3.75cm

Volume = Area of piston x difference in compression height

Volume = PI x (3.75) ^ 2 x 0.07

Volume = 3.1416 x 14.062 x 0.07 = 3,09 cc


3-Volume added by dish:

The dish is 6mm deep with truncated cone shape. (. The larger diameter is 58mm and the smaller one is 45mm)

R=58/2 = 29mm = 2.9cm
r =45/2 = 22.5mm = 2.25cm
h=6mm = 0.6cm

V=h x PI/3 x (R^2 + Rxr + r^2) this is the volume of a truncated cone.

V= 12.56 cc


4-New chamber volume

So, the new chamber has:

NCV = Stock Volume + Dish volume + Top volume (compression height)

NCV = 36.07cc + 12.56cc + 3.09cc = 51.72cc


5-New cylinder volume:

The piston has now 75mm diameter, so, the new volume is:

r= 75mm/2 = 37.5mm = 3.75cm
h= stroke = 75.5mm = 7.55cm

Cyl vol = PI x (3.75^2) x 7.55 = 333.55 cc


6- New compression ratio:

CR = (Cyl vol + NCV)/(NCV) = 7.44


If we consider the valve cut-outs and , which are a bit larger for the vitara pistons, The CR gets slightly lower, around 7.3 for a 1cc difference in valve cut-outs, but it's still an assumption. So, CR is around 7.3~7.5

For the other pistons, with smaller dish, doing the same calculation, CR is 7.7~7.9

Deshrouding the valves and polishing the chamber leads to even lower CR depending on the job.

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PostPosted: Tue Jun 20, 2006 2:30 am 
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Thank you very much for the calculations Caaarlo, I understand a lot better now.
Have you made your final decision on choice of pistons yet then? and are you considering skiming the block and head to higher the compression ratio slightly?

These are the ones I put into my engine...
http://www.turboproject.pwp.blueyonder. ... coated.jpg

Phil


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PostPosted: Tue Jun 20, 2006 8:23 am 
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Well, 7 is quite low for the boost level I intend to use (below 15psi). I don't know yet. If I can get the other ones with smaller dish, then I will install those to have at least 7.7. Otherwise, I will probably stay with stock compression and lower boost.

Another option would be to install G13BB pistons for Suzuki Jimny which lower the CR to around 9 on a stock head and maybe mid eights for a worked chamber. I am talking about this piston (left):

Image

So far, theoretical and approximate CRs with stock G13B head would be

G13BB = ~8.8
Vitara 4mm = 7.9~7.7
Vitara 6mm = 7.5~7.3


Could someone please measure these values on an actual engine ?

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PostPosted: Tue Jun 20, 2006 9:11 pm 
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I don't think you would dip below 8:1 compression ratio with either set of Vitaras. From my understanding, with a completely stock head, it's more like 8.5:1.

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PostPosted: Tue Jun 20, 2006 9:58 pm 
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Yes, I wanted to dismitify the legend. Everybody thinks it is 8.5, but nobody actually measured it, or the ones who did it, haven't posted their results. Even me, I bought the pistons thinking they were around 8.5 because everyone was repeating "Vitaras lower CR to 8.5" in unison. But once I had them here... surprise !!!

I have found some posts where people is surprised to get around 7 CR with vitaras, and they ask themselves where did they screw up, thinking they should get 8.5.

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PostPosted: Tue Jun 20, 2006 10:24 pm 
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The eight of the pistons acount for the lower compression ratio you're getting Caarlo. I noticed some pistons manufacturer aren't paying much attention about how close their parts are to the OEM ones. I've seen similar things hapenning to the DSM guys. You should get a set of OEM pistons and see how they compare.


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PostPosted: Tue Jun 20, 2006 10:30 pm 
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I have made the calculations according to piston specifications found in several manufacturers like TOTO (japanese, probably the manufacturer of OEM pistons), JCC, YCP, CKT, ARCO and TIK (all have the same, maybe 0.1mm difference in compression height), and not my actual piston dimensions.

Measured the piston with a caliper, and they are quite accurate compared to the specifications. Compression height, dish depth, piston lengh, diameter, they are ok. So, If I wanted to calculate the actual CR for my pistons, the numbers should be pretty close.

I have returned the pistons, and requested some G13BB ones if available.

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PostPosted: Tue Jun 20, 2006 11:08 pm 
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Caaarlo wrote:
Yes, I wanted to dismitify the legend. Everybody thinks it is 8.5, but nobody actually measured it, or the ones who did it, haven't posted their results. Even me, I bought the pistons thinking they were around 8.5 because everyone was repeating "Vitaras lower CR to 8.5" in unison. But once I had them here... surprise !!!

I have found some posts where people is surprised to get around 7 CR with vitaras, and they ask themselves where did they screw up, thinking they should get 8.5.


here here, i second this move ... i too would really love to know what CR i'm running...

From reading teamswift forums i was made to believe that vitara pistons on a stock head would be about 8.5-9.0:1 CR

if its really 7.6:1 well that would be something ...time to bump my timing further !!!

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PostPosted: Tue Jun 20, 2006 11:11 pm 
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Jardamuth wrote:
The eight of the pistons acount for the lower compression ratio you're getting Caarlo. I noticed some pistons manufacturer aren't paying much attention about how close their parts are to the OEM ones. I've seen similar things hapenning to the DSM guys. You should get a set of OEM pistons and see how they compare.


This is a big jump in CR from 8.5-9.0:1 to 7.6:1 don't ya think ....

the ones that caaarlo had the "6mm dish" are the same ones i got my my suzuki dealers, and those are SGP !!!

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PostPosted: Tue Jun 27, 2006 9:39 am 
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But does it matter that the cr is less then what was excpected? I mean look at all the guys using these pistons with good results in there turbo projects.
If it works then why not use it?
Ryan


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PostPosted: Tue Jun 27, 2006 10:30 am 
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FiveZigen wrote:
But does it matter that the cr is less then what was excpected? I mean look at all the guys using these pistons with good results in there turbo projects.
If it works then why not use it?
Ryan


off boost performance ...
even thou i don't have a problem i just adjust timing , but you can go so far with timing and now more.

also efficiency is another prob

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PostPosted: Thu Jun 29, 2006 1:34 am 
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i'm not much of a genius but listen to this............

lets say a stock gti has 210psi cylinder pressure along with the fact that we all know that the compression ratio is 10:1.

could we then say........... 210/10 = 21 ------- call this alpha

then lets say the new cylinder psi = 170psi....... with the low compression pistons after installation.

we could then say that 170/21 (alpha) = 8.1.......... which would be the new compression ratio.

i mean this eliminates a lot of confusion and accomodates all the variations in piston height, dish, chamber volume, groove depth etc....


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PostPosted: Thu Jun 29, 2006 6:10 am 
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i think there is a difference between static compresion ratio ans what yours on about badboyscyari. :?:


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