best compression for twin turbo
03-28-2005, 09:47 PM
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best compression for twin turbo have 03 c5 received my ptk kit with twin te44. here is my dilama, i have a forged short block built assuming that i would use my patriot 59cc heads. well i pulled heads off my current set up and engine guy now says that i should look at a head thats has thicker deck! so i am looking at afr 205 but 66 cc is small as they get. that equates to 8.37 is that to low.
whats the best compression to run? ill wanna max effort but not some drag only setup. what happens if comp. is too low?
whats the best compression to run? ill wanna max effort but not some drag only setup. what happens if comp. is too low?
03-28-2005, 09:54 PM
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Originally Posted by eviltwins
8.37:1 will run great, you won't notice a difference from 9:1 on the street but you'll be able to run a crapload more boost on pump gas.
cannot i bump up timing to elevate any lazyness off boost?
how much boost do think i can run on 94?
03-28-2005, 09:58 PM
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Yes you can compensate some with adding timing down low. Alot of people on other boards are still clueless when it comes to building a turbo setup.
Jose
Jose
03-28-2005, 10:08 PM
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Originally Posted by JZ 97 SS 1500
Yes you can compensate some with adding timing down low. Alot of people on other boards are still clueless when it comes to building a turbo setup.
Jose
Jose
jose, i posted over there and tell me ill have a dog off boost w/that low compression
whats the difference in compression on ls1 versus ls6? so if i drove stock c5 and then drove z06 i would notice big difference in torque at low part throttle? i dont think so. ls1 has about .5 poiunt less compression?
03-29-2005, 06:28 AM
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nick- i read that thread on corvette forum and if i felt like logging in i would've given some opinion in that thread.
i think what you are doing is PERFECT!. higher compression and fi is very difficult to tune, you run into way more problems getting it right. your car is stalled so i wouldn't worry about the lag too much, it is goiing to be there on any setup regardless of the compression ratio.
another thing is you would NOT want to increace timing off-boost unless you are damn sure it will pull it back during spool, this is a problem some people have (not sure if f-bodies run into this though) and they get alot of kr right during spool/ the beginning of the pull, slowly damaging the enging and killing their power from the lack of timing because of kr. i think you will be allright with this because of the hptuners speed density setup you plan on but it is something to think about/ make sure it is tuned correctly to avoid this.
like said above, lower comp. = safer for the engine and able to run more boost on pumpgas. if you have to run higher boost than an higher comp. motor to make the same power- SO WHAT???! if it is tuned right there is no difference. something i did not see mentioned is the efficiency range of the turbos could help decide on what boost you want to run which could help decide on your comp. ratio delimma.
i think what you are doing is PERFECT!. higher compression and fi is very difficult to tune, you run into way more problems getting it right. your car is stalled so i wouldn't worry about the lag too much, it is goiing to be there on any setup regardless of the compression ratio.
another thing is you would NOT want to increace timing off-boost unless you are damn sure it will pull it back during spool, this is a problem some people have (not sure if f-bodies run into this though) and they get alot of kr right during spool/ the beginning of the pull, slowly damaging the enging and killing their power from the lack of timing because of kr. i think you will be allright with this because of the hptuners speed density setup you plan on but it is something to think about/ make sure it is tuned correctly to avoid this.
like said above, lower comp. = safer for the engine and able to run more boost on pumpgas. if you have to run higher boost than an higher comp. motor to make the same power- SO WHAT???! if it is tuned right there is no difference. something i did not see mentioned is the efficiency range of the turbos could help decide on what boost you want to run which could help decide on your comp. ratio delimma.
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03-29-2005, 02:54 PM
#8
If you want the car to have more low range power and spool the turbo quicker bump the compression to 9:1. Higher compression however will limit overall ultimate boost on 94 octane... but make the low end power much more pleasant to drive as it will have more torque without being under pressure (boost). Always tradeoffs.
If you are at a higher altitude you want to have the compression even higher 9:5:1 etc. Many race teams do this with forced induction setups. NHRA top fuel supercharged guys run 7:1 at low altitude tracks and 8:1+ at mile high in CO.
If it is an all out race motor 8:1 will allow tons of boost... but until you make boost the car will be a little doggy of the line and not spool as quickly.
I'd say leave it alone and see what happens. Your motor is together.... 8:37:1 is a good compression for forced induction, and 347ci flows plenty of air to spool your turbos.
If you don't plan on dumping in 116 octane, bumping the timing, and seeing how much power it'll make set on kill at the track.... I doubt you'll ever start lifting heads due to a thin deck.
Run what you have... and if you think it is a little laggy.... you could always make changes later. Different gear ratio out back, smaller turbine housings spool quicker, or thinner head gaskets to bump compression, different heads (AFR 225's).
A little lag may be a good thing on the street... or you will be blowing the tires off all over the place. Been there.... done that. Not fun.
I think your car with some methanol/alcohol injection in conjunction with the 94 octane allowing you to up the boost even higher once you break the motor in will make it a serious beast. Remember... every 13-14lbs of boost effectively doubles the size of your engine.... at least that was the number that was used when I was heavily into Buick GN's (turbo V6).
Good luck... I think your car will be beast as it is and have good driveability. Hardcore GN guys run around on the street with 8:1 compression 231ci engines, TE-63 or larger turbos, and the driveability is good. Hardest thing on the street is traction.
If you want to spool quickly off the line when racing get a 2 step from Harlan
.
Good luck,
Mark
If you are at a higher altitude you want to have the compression even higher 9:5:1 etc. Many race teams do this with forced induction setups. NHRA top fuel supercharged guys run 7:1 at low altitude tracks and 8:1+ at mile high in CO.
If it is an all out race motor 8:1 will allow tons of boost... but until you make boost the car will be a little doggy of the line and not spool as quickly.
I'd say leave it alone and see what happens. Your motor is together.... 8:37:1 is a good compression for forced induction, and 347ci flows plenty of air to spool your turbos.
If you don't plan on dumping in 116 octane, bumping the timing, and seeing how much power it'll make set on kill at the track.... I doubt you'll ever start lifting heads due to a thin deck.
Run what you have... and if you think it is a little laggy.... you could always make changes later. Different gear ratio out back, smaller turbine housings spool quicker, or thinner head gaskets to bump compression, different heads (AFR 225's).
A little lag may be a good thing on the street... or you will be blowing the tires off all over the place. Been there.... done that. Not fun.
I think your car with some methanol/alcohol injection in conjunction with the 94 octane allowing you to up the boost even higher once you break the motor in will make it a serious beast. Remember... every 13-14lbs of boost effectively doubles the size of your engine.... at least that was the number that was used when I was heavily into Buick GN's (turbo V6).
Good luck... I think your car will be beast as it is and have good driveability. Hardcore GN guys run around on the street with 8:1 compression 231ci engines, TE-63 or larger turbos, and the driveability is good. Hardest thing on the street is traction.
If you want to spool quickly off the line when racing get a 2 step from Harlan
.Good luck,
Mark
03-29-2005, 03:21 PM
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every 13-14lbs of boost effectively doubles the size of your engine.... at least that was the number that was used when I was heavily into Buick GN's (turbo V6).
03-29-2005, 03:39 PM
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is there any difference in the compression needed between twin turbo or single? or does it only matter how much air is flowing?
say, you have single turbo setup that flows 800 cfm(i dont know what they really flow, but lets just use it for example) and you have a twin turbo setup that also flows 800 cfm. will that decide the comprssion needed, or is there something im missing?
say, you have single turbo setup that flows 800 cfm(i dont know what they really flow, but lets just use it for example) and you have a twin turbo setup that also flows 800 cfm. will that decide the comprssion needed, or is there something im missing?
03-29-2005, 07:06 PM
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Originally Posted by JZ 97 SS 1500
Yes you can compensate some with adding timing down low. Alot of people on other boards are still clueless when it comes to building a turbo setup.
Jose
Jose
How can anyone make a bold face recommendation with out asking the particulars and preferences. Even the most basic questions like fuel and boost level were not asked before people started flappin.
Long live the internet.
Dave
... 
03-29-2005, 11:19 PM
#14
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Lower compression means:
-more room for more rwhp on pump gas
-will need more boost to hit same rwhp number as higher compression engine (8:1 vs 9:1 for example)
-lowend lag is a ridiculous concept when you have a turbo setup that makes peak torque at 4000rpms. don't listen to those guys.
I run a 8-8.3:1 348ci right now. I make over 700rwhp at 5700 rpms. I have a 4500 stall.
-more room for more rwhp on pump gas
-will need more boost to hit same rwhp number as higher compression engine (8:1 vs 9:1 for example)
-lowend lag is a ridiculous concept when you have a turbo setup that makes peak torque at 4000rpms. don't listen to those guys.
I run a 8-8.3:1 348ci right now. I make over 700rwhp at 5700 rpms. I have a 4500 stall.
03-30-2005, 08:45 AM
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" -lowend lag is a ridiculous concept when you have a turbo setup that makes peak torque at 4000rpms. don't listen to those guys."
Yes, but off-idle or tip-in performance can suffer when you remove too much compression. You might not notice it depending on how car is driven and depending on transmission/gearing but you do lose some, likely small amounts of low end torque. If you drive pretty aggresively you probably won't notice anything. On larger cube engines any loss would likely be negated.
But given the way most of y'all drive your cars no one cares about slow takeoffs from a stoplight
Yes, but off-idle or tip-in performance can suffer when you remove too much compression. You might not notice it depending on how car is driven and depending on transmission/gearing but you do lose some, likely small amounts of low end torque. If you drive pretty aggresively you probably won't notice anything. On larger cube engines any loss would likely be negated.
But given the way most of y'all drive your cars no one cares about slow takeoffs from a stoplight
03-30-2005, 10:12 AM
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Dave... I think you are splitting hairs.
I have had a stock engine, a 12:1 422ci iron block na setup, a 9:1 motor and now a 8:1 motor. They all drive the same down low. My butt-o-meter can't tell the difference. The only difference frankly has been the crappier driveability of my old n/a 244/244//112 vs the cams I have had with FI.
When you are playing the 600-800rwhp game you have to decide beforehand what gas you will use, what power level you are shooting for, and how streetable you want the combo.
FYI when I went from 9:1 to 8:1 the expectation was that I would need to make 1 more lb of boost just to hit the same old numbers... to make up for the compression drop.
I have had a stock engine, a 12:1 422ci iron block na setup, a 9:1 motor and now a 8:1 motor. They all drive the same down low. My butt-o-meter can't tell the difference. The only difference frankly has been the crappier driveability of my old n/a 244/244//112 vs the cams I have had with FI.
When you are playing the 600-800rwhp game you have to decide beforehand what gas you will use, what power level you are shooting for, and how streetable you want the combo.
FYI when I went from 9:1 to 8:1 the expectation was that I would need to make 1 more lb of boost just to hit the same old numbers... to make up for the compression drop.
06-10-2016, 01:34 PM
#18
Twin turbo Ok I am thinking of doing an ls2 with ls3 heads. And twin turbos. What's a good cam recommendation?
With the head ls2 seat up should be 10.4 should I do thicker gaskets to get less compression
With the head ls2 seat up should be 10.4 should I do thicker gaskets to get less compression
06-10-2016, 02:11 PM
#19
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