TeamSwift

Home of the Suzuki mini-compacts ! Your Home for all things Suzuki Swift, Geo Metro, Holden Barina, Chevy Sprint, Pontiac Firefly, and Suzuki Cultus. TeamSwift is a technical performance oriented community!
It is currently Wed Nov 22, 2017 4:45 pm

Underbody braces, turbos and more!

All times are UTC - 5 hours




Post new topic Reply to topic  [ 43 posts ]  Go to page 1, 2  Next
Author Message
 Post subject:
PostPosted: Mon Jun 19, 2006 12:07 pm 
Offline
User avatar

Joined: Mon May 27, 2002 11:47 pm
Posts: 1974
Location: San Juan, Argentina
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.

_________________
Megasquirt tutorial --- http://caaarlo.50megs.com


Top
 Profile  
 
 Post subject:
PostPosted: Tue Jun 20, 2006 2:30 am 
Offline
User avatar

Joined: Wed Oct 22, 2003 7:35 am
Posts: 477
Location: West Midlands, UK
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


Top
 Profile  
 
 Post subject:
PostPosted: Tue Jun 20, 2006 8:23 am 
Offline
User avatar

Joined: Mon May 27, 2002 11:47 pm
Posts: 1974
Location: San Juan, Argentina
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 ?

_________________
Megasquirt tutorial --- http://caaarlo.50megs.com


Top
 Profile  
 
 Post subject:
PostPosted: Tue Jun 20, 2006 9:11 pm 
Offline
User avatar

Joined: Sun Oct 24, 2004 3:31 pm
Posts: 466
Location: Wahoo, Nebraska
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.

_________________
93' Suzuki Swift Gt Turbo


Top
 Profile  
 
 Post subject:
PostPosted: Tue Jun 20, 2006 9:58 pm 
Offline
User avatar

Joined: Mon May 27, 2002 11:47 pm
Posts: 1974
Location: San Juan, Argentina
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.

_________________
Megasquirt tutorial --- http://caaarlo.50megs.com


Top
 Profile  
 
 Post subject:
PostPosted: Tue Jun 20, 2006 10:24 pm 
Offline
The mad quebecer
The mad quebecer
User avatar

Joined: Thu Nov 07, 2002 10:06 pm
Posts: 4569
Location: Chicoutimi, Québec
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.


Top
 Profile  
 
 Post subject:
PostPosted: Tue Jun 20, 2006 10:30 pm 
Offline
User avatar

Joined: Mon May 27, 2002 11:47 pm
Posts: 1974
Location: San Juan, Argentina
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.

_________________
Megasquirt tutorial --- http://caaarlo.50megs.com


Top
 Profile  
 
 Post subject:
PostPosted: Tue Jun 20, 2006 11:08 pm 
Offline
User avatar

Joined: Thu Aug 28, 2003 6:34 am
Posts: 383
Location: Jamaica W.I.
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 !!!

_________________
Keep it real
GTi Turbo [Microtech LT-8 Stand Alone ECU]
17psi Water Injected
203whp & 182 torque


Top
 Profile  
 
 Post subject:
PostPosted: Tue Jun 20, 2006 11:11 pm 
Offline
User avatar

Joined: Thu Aug 28, 2003 6:34 am
Posts: 383
Location: Jamaica W.I.
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 !!!

_________________
Keep it real
GTi Turbo [Microtech LT-8 Stand Alone ECU]
17psi Water Injected
203whp & 182 torque


Top
 Profile  
 
 Post subject:
PostPosted: Tue Jun 27, 2006 9:39 am 
Offline

Joined: Mon Sep 10, 2001 5:07 pm
Posts: 553
Location: Ontario, Canada
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


Top
 Profile  
 
 Post subject:
PostPosted: Tue Jun 27, 2006 10:30 am 
Offline
User avatar

Joined: Thu Aug 28, 2003 6:34 am
Posts: 383
Location: Jamaica W.I.
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

_________________
Keep it real
GTi Turbo [Microtech LT-8 Stand Alone ECU]
17psi Water Injected
203whp & 182 torque


Top
 Profile  
 
 Post subject:
PostPosted: Thu Jun 29, 2006 1:34 am 
Offline
User avatar

Joined: Thu Jul 03, 2003 11:40 pm
Posts: 174
Location: Jamaica, Kingston
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....


Top
 Profile  
 
 Post subject:
PostPosted: Thu Jun 29, 2006 6:10 am 
Offline

Joined: Sat Aug 07, 2004 11:14 pm
Posts: 46
Location: Australia
i think there is a difference between static compresion ratio ans what yours on about badboyscyari. :?:


Top
 Profile  
 
 Post subject:
PostPosted: Thu Jun 29, 2006 8:40 am 
Offline
User avatar

Joined: Mon May 27, 2002 11:47 pm
Posts: 1974
Location: San Juan, Argentina
Yes, one thing is Compression, and another thing is Compression Ratio.

Anyway, did you get those values on the smaller dish pistons or the deeper ones ?

_________________
Megasquirt tutorial --- http://caaarlo.50megs.com


Top
 Profile  
 
 Post subject:
PostPosted: Thu Jun 29, 2006 8:42 am 
Offline
User avatar

Joined: Thu Aug 28, 2003 6:34 am
Posts: 383
Location: Jamaica W.I.
Caaarlo wrote:
Yes, one thing is Compression, and another thing is Compression Ratio.

Anyway, did you get those values on the smaller dish pistons or the deeper ones ?


ian is that 170psi from the pistons caarlo posted above?

I think i'll try and get the compression test from my car today and post it ...

...

_________________
Keep it real
GTi Turbo [Microtech LT-8 Stand Alone ECU]
17psi Water Injected
203whp & 182 torque


Top
 Profile  
 
 Post subject:
PostPosted: Thu Jun 29, 2006 9:54 am 
Offline
User avatar

Joined: Thu Jul 03, 2003 11:40 pm
Posts: 174
Location: Jamaica, Kingston
i have seen this done on a honda before

jus the same.......... one of my friends bought pistons for his honda that were to raise his compression to 12.5:1 from 11:1 and we did the same static compression test and the maths i did worked out right.........

to me (my opinion) if you have a higher compression ratio, u must have a linear increase in static compression because they are both related to the same cylinder. makes sense to me and numbers dont lie.

is as if you finding the area and volume of a cup of water..... more surface area = more volume, in one way or another


Top
 Profile  
 
 Post subject:
PostPosted: Thu Jun 29, 2006 10:38 am 
Offline
User avatar

Joined: Thu Aug 28, 2003 6:34 am
Posts: 383
Location: Jamaica W.I.
Ok sounds good but was the 170 from a swift with the low compression pistons?

_________________
Keep it real
GTi Turbo [Microtech LT-8 Stand Alone ECU]
17psi Water Injected
203whp & 182 torque


Top
 Profile  
 
 Post subject:
PostPosted: Thu Jun 29, 2006 11:16 am 
Offline
User avatar

Joined: Mon May 27, 2002 11:47 pm
Posts: 1974
Location: San Juan, Argentina
Absolutely right. Number don't lie... only if you take everything into account. As far as I know, compression is not linearly related to compression ratio.

Either way, what kind of pistons do you have ?? because I have calculated one piston to have around 7.4 and the other one to have around 7.9. Which is pretty close to my calculations. Did you shave your head or something ? Maybe this explains why you're having such a good compression while most people is getting ~150 psi from the deep dish vitara pistons.

_________________
Megasquirt tutorial --- http://caaarlo.50megs.com


Top
 Profile  
 
 Post subject:
PostPosted: Fri Jun 30, 2006 6:39 am 
Offline
User avatar

Joined: Wed Oct 22, 2003 7:35 am
Posts: 477
Location: West Midlands, UK
I was getting 165 - 170psi compression with the deeper dish pistons, but the block looked like it had been skimmed quite a bit in its life compared to another block I have.
Phil


Top
 Profile  
 
 Post subject:
PostPosted: Mon Jul 03, 2006 4:54 pm 
Offline
User avatar

Joined: Thu Jan 09, 2003 4:14 pm
Posts: 796
Location: Reykjavik
7.4:1 is absolutely perfect for a turbo engine, run 30psi boost and shut the hell up :razz:


Top
 Profile  
 
PostPosted: Wed Jan 28, 2009 8:19 pm 
Offline

Joined: Wed Jul 12, 2006 5:44 am
Posts: 246
These are some interesting calculations, I just bought myself a set of 75,5mm Deep Dish Vitaras. The motor is going to be machined soon and ill measure when its assembled in the negine the actually findings.


Top
 Profile  
 
PostPosted: Fri Apr 10, 2009 1:05 pm 
Offline
User avatar

Joined: Mon May 27, 2002 11:47 pm
Posts: 1974
Location: San Juan, Argentina
Ricardo, can you post your findings ? Did you measure the actual compression ratio ?

_________________
Megasquirt tutorial --- http://caaarlo.50megs.com


Top
 Profile  
 
PostPosted: Sat Apr 11, 2009 11:13 pm 
Offline

Joined: Wed Nov 19, 2003 12:33 am
Posts: 410
Location: Atlanta,GA Havana,Cuba
please! :wink:

_________________
Bong,Bong,Bong....zuki's


Top
 Profile  
 
PostPosted: Mon Apr 13, 2009 2:50 am 
Offline

Joined: Wed May 17, 2006 1:53 am
Posts: 237
Location: london
i just done a compression test the other day on a different motor[2.0] which was just rebuild and this is with supposedly 8.3-1 compression ratio and we got 125psi however it hadent even ben started yet so runing in will make a difference and that was cold and dry

steve

_________________
N/A THE EXPENSIVE WAY TO GO SLOW
www.uk-ssgti.com


Top
 Profile  
 
PostPosted: Tue Apr 14, 2009 6:29 pm 
Offline
User avatar

Joined: Mon May 27, 2002 11:47 pm
Posts: 1974
Location: San Juan, Argentina
stevegti2 wrote:
i just done a compression test the other day on a different motor[2.0] which was just rebuild and this is with supposedly 8.3-1 compression ratio and we got 125psi however it hadent even ben started yet so runing in will make a difference and that was cold and dry

steve


Well, but this has nothing to do with a 1.3 + Vitara pistons. Furthermore, cylinder compression depends on the cam profile and health of the engine internals. Therefore Compression Ratio is a more descriptive parameter than cylinder compression.

_________________
Megasquirt tutorial --- http://caaarlo.50megs.com


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 43 posts ]  Go to page 1, 2  Next

All times are UTC - 5 hours


Who is online

Users browsing this forum: No registered users and 4 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group