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#1
12-05-2004, 03:06 AM
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Pros and Cons on lowering C/R in 4g63-T
I was just thinkin about this and just needed answers.
-the C/R in a stock 4g63-T, GSX,GS-T, is about 8.5:1, rite? well, i wanna lower my c/r to 8.0:1, and is it possible? What is the lowest C/R in any DSM? And when i do this, what are the pros and cons to lowering the c/r in a 4g63-T motor? thanks...Silver_GTR34
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"i told you it was third, I lengthen the injector pulse another millisec and tuned the NOS timer, and you'll run nines" --2OF9-- (DSM team specialist) ;D #808/1000 
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#2
12-05-2004, 02:17 PM
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Re: Pros and Cons on lowering C/R in 4g63-T
less compression makes it so you can run more boost. but it makes the response worse before your turbo kicks in. i think hks sells a thich headgasket to use to lower the CR. other people just stack 2 oem gaskets
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-1stGenRocks- 95 Tsi AWD: 6 bolt, DSMLink, 880's, ACT 2600, lightweight flywheel, AGX's, Dropzone springs, poly motor mounts and suspension bushings, 3 inch turboback, gus modded 1g BOV, hardpipes, drilled & slotted rotors, 17's plans: bastard 20g, water/meth injection NO FMIC
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#3
12-05-2004, 03:50 PM
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are you going to run Nos?
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#4
12-05-2004, 05:13 PM
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Re: Pros and Cons on lowering C/R in 4g63-T
^^^
 (saw the oppturnity to use this pic and i am ging to use it)
__________________
 1998 Eagle Talon TSi AWD 6 Bolt Swap \ DSMLink V2.5 \ ACT 2100 clutch \ PTE SCM 61 \ Forge MBC@28psi \ VPE O2 Housing \ MR Downpipe \ Thermal R&D Cat-Back \ Tial 38mm WG dumping off O2 \ FMIC w\ in short route \ AFPR setup/walbro 255hp \ PTE 880cc injectors \ Crower Ti retianers \ Crower Springs \ Crower 64414 (stage 3 race) cams \ Ferrea valves \ 3.5 bar MAP \ PLX M-300 Wideband
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#5
12-05-2004, 05:36 PM
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Re: Pros and Cons on lowering C/R in 4g63-T
nah, no nos, hate nos. butta, im jus wondering because i thought with less c/r i can put like a 18g turbo in with the "back-up" mods with the lower c/r. Do you guys know whats the lowsest c/r a dsm can handle.
__________________
"i told you it was third, I lengthen the injector pulse another millisec and tuned the NOS timer, and you'll run nines" --2OF9-- (DSM team specialist) ;D #808/1000
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#6
12-05-2004, 07:43 PM
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Re: Pros and Cons on lowering C/R in 4g63-T
low compression is good...to a point...when you start getting lower than 7.5:1 or even 8:1 is as low as you should go ...yes you can run more boost ...but inturn you losing alot of throttle responce and bottom end power....when you start getting to be like Kevin where your car is setup for racing and you have reinforced internals then you up the compression and the boost to get the best of both worlds...what are you running Kevin? 9:1? 9.5:1? 10:1?
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1998 Eagle Talon TSi AWD 6 Bolt Swap \ DSMLink V2.5 \ ACT 2100 clutch \ PTE SCM 61 \ Forge MBC@28psi \ VPE O2 Housing \ MR Downpipe \ Thermal R&D Cat-Back \ Tial 38mm WG dumping off O2 \ FMIC w\ in short route \ AFPR setup/walbro 255hp \ PTE 880cc injectors \ Crower Ti retianers \ Crower Springs \ Crower 64414 (stage 3 race) cams \ Ferrea valves \ 3.5 bar MAP \ PLX M-300 Wideband
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#7
12-05-2004, 08:51 PM
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Re: Pros and Cons on lowering C/R in 4g63-T
Kevin's compression is a special case. If you read some of his latest lengthy threads about why his last motor blew, it says he was running too high compression, not something that it recommended for most people. Personally I don't know what is best, I would go for 8.5 pistons.
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#8
12-06-2004, 08:03 PM
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Re: Pros and Cons on lowering C/R in 4g63-T
yeah, i thought higher compression ratio was not such a good idea for turbo cars...
__________________
"i told you it was third, I lengthen the injector pulse another millisec and tuned the NOS timer, and you'll run nines" --2OF9-- (DSM team specialist) ;D #808/1000
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#9
12-06-2004, 08:36 PM
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Re: Pros and Cons on lowering C/R in 4g63-T
^^you do get more hp but only for a short time, untill somthing breaks
__________________
1998 Eagle Talon TSi AWD 6 Bolt Swap \ DSMLink V2.5 \ ACT 2100 clutch \ PTE SCM 61 \ Forge MBC@28psi \ VPE O2 Housing \ MR Downpipe \ Thermal R&D Cat-Back \ Tial 38mm WG dumping off O2 \ FMIC w\ in short route \ AFPR setup/walbro 255hp \ PTE 880cc injectors \ Crower Ti retianers \ Crower Springs \ Crower 64414 (stage 3 race) cams \ Ferrea valves \ 3.5 bar MAP \ PLX M-300 Wideband
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#10
12-10-2004, 11:18 PM
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Re: Pros and Cons on lowering C/R in 4g63-T
yep^^^^^
butta, how is lower C/R good for NOS? i still dont really get the C/R things yet. Can some one tell me. Well, what i've studied is that with higher c/r, you'll produce lots of power fast, but with turbo its bad because of all the "pressure" turbo puts into a high c/r...but thats not the point of c/r, i know theres alot more, can some1 help me? thanks!
__________________
"i told you it was third, I lengthen the injector pulse another millisec and tuned the NOS timer, and you'll run nines" --2OF9-- (DSM team specialist) ;D #808/1000
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#11
12-11-2004, 12:14 AM
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Re: Pros and Cons on lowering C/R in 4g63-T
It's not about pressure on the turbo. There are all of these factors that develop power, but get you closer to knock.
Do you want an 11:1 motor that runs 5psi and knocks, a 7:1 motor that can run 35psi before it knocks, or do it like everyone else and have a balance of compression, boost and timing? Are you ready to be purchasing these items? Call SBR, RRE, magnus, etc and ask them what kind of pistons to get. They will ask you a few questions and give you an answer. I don't know what kind of DSM you are building, if you are even going to get pistons at all.
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#12
12-11-2004, 12:27 AM
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Re: Pros and Cons on lowering C/R in 4g63-T
Alrite man, thanks bro. thats all i needed to kno. thanks JoeWagon.
i dunno wut i want yet, prolly high boost or just a totally balance engine. but thanks for the info!
__________________
"i told you it was third, I lengthen the injector pulse another millisec and tuned the NOS timer, and you'll run nines" --2OF9-- (DSM team specialist) ;D #808/1000
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#13
12-22-2004, 02:26 PM
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Re: Pros and Cons on lowering C/R in 4g63-T
Most pistons are only available in 8.5 to 9:1 for our cars. Its what works best. Stock 1g was 7.8:1, and when I went from the 2g 8.5:1 to that 6 bolt, I could really feel the loss of off boost power. I'm inclined to believe that what most people call lag from the 1g head, is really loss of off boost power from the lower CR
 In my case CR was supposed to end up at 8.8:1. For whatever reason (cam timing is the primary suspect) it was closer to 10:1. Now, I still ran well at this level. But one little mistake and you could be in big trouble. Using a thicker gasket is a bad idea. It will increase quench height reducing the squish effect. That will often make you more likely to knock, despite the lower CR! Keep quench height to 030-040 whenever possible. Make sure cams are timed correctly (degreed). 8.5:1 will work fine, as will 1g 7.8:1. Look at all the poeple making shitloads of power, even on pump gas, on stock compression. Hope that helps.
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Kevin Jewer RWD Talon - 7.92 at 180 Mightymax - 10.7 at 125
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