Homepage Garage Wiki Register Members List Social Groups Calendar Search Today's Posts Mark Forums Read
#Camaro6
Go Back   CAMARO6 > Engine | Drivetrain | Powertrain Technical Discussions > Forced Induction Discussions


BeckyD @ James Martin Chevy


Post Reply
 
Thread Tools
Old 09-16-2018, 08:02 AM   #1
L78toLT1
 
L78toLT1's Avatar
 
Drives: Hyper Blue 2016 2SS 6M
Join Date: Sep 2017
Location: North Ga
Posts: 245
Optimum compression ratio

I'm adding lt4 fueling and a cam kit to my Maggie equipped SS this winter and I'm on the fence regarding swapping out the stock pistons. I'm working with Ted Jannetty on my build but thought I would post my question here rather than calling Ted direct to help out and get input from other members.
When swapping pistons on a FI motor, is it best to drop the compression a point or so? There appear to be pistons/piston rod combos available that will retain the stock compression ratio or drop it a point or so.
I expect that lower compression is advantageous at extremely high levels of boost. I'll probably be somewhere around 10 - 12 psi.
__________________
Baby Blue
2016 hyper blue 2SS/6m/MRC/NPP/Rotofab dry/Pray ported TB/Magnuson Heartbeat 95mm pulley JRE tuned/Kooks 1 7/8 Long tubes with high flow cats
L78toLT1 is offline   Reply With Quote
Old 09-16-2018, 08:10 AM   #2
Rlhay2
 
Rlhay2's Avatar
 
Drives: 2017 ZL1
Join Date: Mar 2014
Location: DFW, TX
Posts: 175
What fuel are you willing to run?

This question is more pertinent than your desired boost level.
Rlhay2 is offline   Reply With Quote
Old 09-16-2018, 08:20 AM   #3
L78toLT1
 
L78toLT1's Avatar
 
Drives: Hyper Blue 2016 2SS 6M
Join Date: Sep 2017
Location: North Ga
Posts: 245
Quote:
Originally Posted by Rlhay2 View Post
What fuel are you willing to run?

This question is more pertinent than your desired boost level.
As much e85 as I can get away with. I'd love to be able to run e85 exclusively but recognize that I will probably need to stay around 70%
__________________
Baby Blue
2016 hyper blue 2SS/6m/MRC/NPP/Rotofab dry/Pray ported TB/Magnuson Heartbeat 95mm pulley JRE tuned/Kooks 1 7/8 Long tubes with high flow cats
L78toLT1 is offline   Reply With Quote
Old 09-16-2018, 08:51 AM   #4
KingLT1

 
KingLT1's Avatar
 
Drives: 2016 1SS NFG A8
Join Date: Aug 2017
Location: 46804
Posts: 1,295
If running E85 don't touch the compression... pump gas only, drop it a point.
__________________
[2016 NFG 1SS A8][Leather/NPP][Pray Ported IM/TB/Rotofab/Flex Fuel/CA ORP]
KingLT1 is offline   Reply With Quote
Old 09-16-2018, 09:24 AM   #5
Rlhay2
 
Rlhay2's Avatar
 
Drives: 2017 ZL1
Join Date: Mar 2014
Location: DFW, TX
Posts: 175
I am not a tuner but generally, compression is your friend.
If your car is likely to never see 87 octane (or lower) with a good tune you can safely run higher than stock compression. Being DI, pre-ignition is even less likely.

All this said, consult the tuner you intend to use. Ultimately, it's between you two if you are not pleased with the end result.
Rlhay2 is offline   Reply With Quote
Old 09-16-2018, 09:56 AM   #6
wnta1ss
 
Drives: 2017 Camaro 1SS
Join Date: Aug 2016
Location: NH
Posts: 616
My opinion is, if you are only going to have LT4 fuel parts with a cam lobe, running E85, then you will not be able to run enough boost to justify lowering the compression ratio (due to limited fuel supply). Lowering the compression ratio actually makes the engine less efficient, and you'd need to then up the boost just to get back to where you are right now. So unless you are doing a setup to run quite a bit of boost, I think that lowering the CR would be a step backwards. Therefore, with the parts and fuel that you're listing, I think that the drop-in pistons from Vengeance Racing (stock CR) would be a better choice than the lowered-CR pistons.
wnta1ss is offline   Reply With Quote
Old 09-16-2018, 10:06 AM   #7
parish8

 
Drives: 17 SS a8
Join Date: Feb 2010
Location: omaha
Posts: 1,066
Quote:
Originally Posted by wnta1ss View Post
My opinion is, if you are only going to have LT4 fuel parts with a cam lobe, running E85, then you will not be able to run enough boost to justify lowering the compression ratio (due to limited fuel supply). Lowering the compression ratio actually makes the engine less efficient, and you'd need to then up the boost just to get back to where you are right now. So unless you are doing a setup to run quite a bit of boost, I think that lowering the CR would be a step backwards. Therefore, with the parts and fuel that you're listing, I think that the drop-in pistons from Vengeance Racing (stock CR) would be a better choice than the lowered-CR pistons.
What he said^^

If you have plenty of compressor and fuel and plan on turning it up then lowering the compression makes sense.
__________________
760 rwhp at 11psi, 6.48@113 1/8th mile, stock motor
1096 rwhp at 22psi, no new ET, drop in rods and pistons
Twins build http://www.camaro6.com/forums/showthread.php?t=465472
Adding port injection http://www.camaro6.com/forums/showth...ghlight=Ms3pro
parish8 is offline   Reply With Quote
Old 09-16-2018, 10:07 AM   #8
L78toLT1
 
L78toLT1's Avatar
 
Drives: Hyper Blue 2016 2SS 6M
Join Date: Sep 2017
Location: North Ga
Posts: 245
Quote:
Originally Posted by wnta1ss View Post
My opinion is, if you are only going to have LT4 fuel parts with a cam lobe, running E85, then you will not be able to run enough boost to justify lowering the compression ratio (due to limited fuel supply). Lowering the compression ratio actually makes the engine less efficient, and you'd need to then up the boost just to get back to where you are right now. So unless you are doing a setup to run quite a bit of boost, I think that lowering the CR would be a step backwards. Therefore, with the parts and fuel that you're listing, I think that the drop-in pistons from Vengeance Racing (stock CR) would be a better choice than the lowered-CR pistons.
Intuitively I agree. In most cases, compression is definitely a good thing, especially on DI motors. I just want to get inputs from others with more experience. I've done numerous NA builds over the past 40 years but am still a newbie regarding forced induction. I wonder why the lt4 has lower compression given it's modest amount of boost?
__________________
Baby Blue
2016 hyper blue 2SS/6m/MRC/NPP/Rotofab dry/Pray ported TB/Magnuson Heartbeat 95mm pulley JRE tuned/Kooks 1 7/8 Long tubes with high flow cats
L78toLT1 is offline   Reply With Quote
Old 09-16-2018, 11:31 AM   #9
KingLT1

 
KingLT1's Avatar
 
Drives: 2016 1SS NFG A8
Join Date: Aug 2017
Location: 46804
Posts: 1,295
The reason why I said what I did was for the simple fact that on stock compression the octane wall is around 700whp with 93 octane. So if you don't plan on supplementing with meth or c16, then dropping compression would be required if you plan on going over 700whp with pump fuel.

That being said I would run E85 at all costs and leave the compression alone unless you plan on building a 1k whp monster, then it might be a good idea to go ahead and lower the compression a point .
__________________
[2016 NFG 1SS A8][Leather/NPP][Pray Ported IM/TB/Rotofab/Flex Fuel/CA ORP]
KingLT1 is offline   Reply With Quote
Old 09-16-2018, 12:43 PM   #10
laynlo15
locrzn
 
laynlo15's Avatar
 
Drives: 2016 1ss A8, Npp
Join Date: Nov 2015
Location: clark, mo
Posts: 3,810
I'm rebuilding my motor right now and I'll be running 10.5 compression. Should have less issues with running higher boost and hopefully less detonation with the lower compression ratio. I run VP Ms 109 and 2-1000 cc nozzles of meth/water. We pushed it pretty hard at 16.5 lbs of boost with the higher compression on the stock Lt1 and turning it a little higher then stock rpm.
__________________
Team Magnuson Heartbeat Driver/Employee, AEM, Lingenfelter BBHP, Lt4 injectors, NW TB. Rpm RB, Hoosier/Racestar, Phastech, Its real Fast. Tuned by Mike(toohighpsi) 713 rwhp/669rwtq
10.03@138 (139.50 best) 1/4 and 6.46@110 1/8 mile
GC Racing Team
laynlo15 is offline   Reply With Quote
Old 09-16-2018, 12:55 PM   #11
laynlo15
locrzn
 
laynlo15's Avatar
 
Drives: 2016 1ss A8, Npp
Join Date: Nov 2015
Location: clark, mo
Posts: 3,810
The drop in piston is still the stock CR. With your 95mm pulley you are probably at about 7 lbs of boost, so your on pretty low boost right now. Stock compression will work best if you plan on running about 10-11 lbs. I plan on running about 17-18 lbs with the new motor.
__________________
Team Magnuson Heartbeat Driver/Employee, AEM, Lingenfelter BBHP, Lt4 injectors, NW TB. Rpm RB, Hoosier/Racestar, Phastech, Its real Fast. Tuned by Mike(toohighpsi) 713 rwhp/669rwtq
10.03@138 (139.50 best) 1/4 and 6.46@110 1/8 mile
GC Racing Team
laynlo15 is offline   Reply With Quote
Old 09-16-2018, 04:33 PM   #12
Drsagacity

 
Drsagacity's Avatar
 
Drives: 2017 Camaro 2SS Nightfall Gray vert
Join Date: Jan 2018
Location: Swansea, IL
Posts: 773
FYI - I did add the forged pistons with the stock compression ratios. I can run full pump e85 which is between e70-80 (apparently the gas stations in Illinois have additional environmental additives that cause the percent e to be reduced).

I have two e gas stations right by my house. The first station's pump has e80 and the other is closer to e70. Once I up to 10psi, I expect that we will be kind of topped out around e70 so I will generally fill-up at the station with e70. At the same time, when I go other places, I will use HP tuner to check my mixture... That should allow me to skip mixing. If I am further away from home and use 93, then I will simply add from the station with higher e until numbers are where I want them.

My intent is to keep the car setup so I don't really have to mix fuels which means staying with about 10psi.

I have started a couple Jannetty Super Street Brawler threads, check those out and see what you think. I worked with Magnuson and Laynlo at first and then went with Ted for the second stage of my setup...couldn't be happier. I am going to have them overnight the pulley to up boost tomorrow
__________________
2017 Camaro 2SS - Nightfall Gray
GC Racing - Magnuson Heartbeat Supercharger w/ Rotofab, 95mm pulley
570rwhp/565 rwtq (7psi)

Jannetty Racing - ZL1 fuel system, BAP, E85, Rough idle cam, Kooks Headers, Forged pistons, front crank seal, Mishimoto CC, 85mm pulley. (80 and 75mm pulleys on way)
705whp/698wtq (8psi)

Appearance: MRR 017’s (PK Designs), Stainlessworks axleback exhaust (RDP Store), Eibach lowering kit (PK Design), chin splitter and side skirts (C7 Carbon), Blackout kit (Big Wormz), LT1 emblems (Emblem Pros)

Last edited by Drsagacity; 09-16-2018 at 06:31 PM.
Drsagacity is online now   Reply With Quote
Old 09-16-2018, 05:56 PM   #13
wnta1ss
 
Drives: 2017 Camaro 1SS
Join Date: Aug 2016
Location: NH
Posts: 616
Quote:
Originally Posted by L78toLT1 View Post
I wonder why the lt4 has lower compression given it's modest amount of boost?
My guess on this one is, because it has a warranty, GM is being extra cautious.
wnta1ss is offline   Reply With Quote
 
Post Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 06:44 PM.


Powered by vBulletin® Version 3.8.9 Beta 4
Copyright ©2000 - 2018, vBulletin Solutions, Inc.