follow ft86club on our blog, twitter or facebook.
FT86CLUB
Ft86Club
Speed By Design
Register Garage Members List Calendar Search Today's Posts Mark Forums Read

Go Back   Scion FR-S Forum | Subaru BRZ Forum | Toyota 86 GT 86 Forum | AS1 Forum - FT86CLUB > Technical Topics > Forced Induction

Forced Induction Turbo, Supercharger, Methanol, Nitrous


User Tag List

Reply
 
Thread Tools Search this Thread
Old 03-13-2019, 02:32 PM   #1
elitegunslinger
Member
 
elitegunslinger's Avatar
 
Join Date: Oct 2016
Drives: 2014 BRZ Limited
Location: NJ
Posts: 82
Thanks: 5
Thanked 14 Times in 12 Posts
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Safe Boost Compression Options

This chart I made utilizing information I've found from previous safe boost levels on the stock motor of 12.5:1 it seems like these engines are good for a final compression of about 22 or less on 91/93 octane (green) and FCR of 35 or less for E85 (orange). I haven't been looking into E85 as it's not readily available in my area.

Compression Vertical and PSI Horizontal


Are there additional factors or limitations of the FA20 platform I should be taking into account before proceeding with building a boosted motor? Any reason there aren't more 13.5 CR boosted FA20 in the wild?

Note:
These are extremely loose numbers and proceed with caution and the guidance of your engine builder / tuner.

Last edited by elitegunslinger; 03-14-2019 at 02:42 PM.
elitegunslinger is offline   Reply With Quote
The Following 2 Users Say Thank You to elitegunslinger For This Useful Post:
Boris_Petrov (03-13-2019), Yobiwan (03-14-2019)
Old 03-13-2019, 02:50 PM   #2
DarkPira7e
New Member
 
DarkPira7e's Avatar
 
Join Date: Feb 2017
Drives: 13 Firestorm Red FRS
Location: Burlington Vermont
Posts: 680
Thanks: 301
Thanked 453 Times in 265 Posts
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
I think the reasoning is that people would rather have the flexibility to run a dynamic CR using boost, rather than fighting knock on a higher static CR engine before boost is added. That, and not many suppliers waste money building higher CR pistons when they know the aftermarket caters towards lowering it.
Very cool chart though
DarkPira7e is offline   Reply With Quote
Old 03-13-2019, 03:52 PM   #3
bfrank1972
Senior Member
 
Join Date: Jul 2013
Drives: 2013 FR-S Argento
Location: Westport,CT
Posts: 1,528
Thanks: 394
Thanked 798 Times in 478 Posts
Mentioned: 7 Post(s)
Tagged: 1 Thread(s)
It's a good rule of thumb reference, but I'd imagine a lot of things come into play, like rpm, cam timing, ignition advance, fuel, cooling etc.
bfrank1972 is offline   Reply With Quote
Old 03-13-2019, 04:53 PM   #4
Boris_Petrov
Member
 
Join Date: Dec 2018
Drives: 2013 GT 86
Location: BG
Posts: 23
Thanks: 21
Thanked 3 Times in 3 Posts
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quote:
Originally Posted by DarkPira7e View Post
I think the reasoning is that people would rather have the flexibility to run a dynamic CR using boost, rather than fighting knock on a higher static CR engine before boost is added. That, and not many suppliers waste money building higher CR pistons when they know the aftermarket caters towards lowering it.
Very cool chart though
What do you mean by dynamic compression?

Sent from my SM-A520F using Tapatalk
Boris_Petrov is offline   Reply With Quote
Old 03-13-2019, 04:54 PM   #5
Boris_Petrov
Member
 
Join Date: Dec 2018
Drives: 2013 GT 86
Location: BG
Posts: 23
Thanks: 21
Thanked 3 Times in 3 Posts
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Does that mean that I can run 20 psi on 12.5 CR safely on 93?

Update: nvm I understood the graph sorry

Sent from my SM-A520F using Tapatalk
Boris_Petrov is offline   Reply With Quote
Old 03-13-2019, 04:57 PM   #6
elitegunslinger
Member
 
elitegunslinger's Avatar
 
Join Date: Oct 2016
Drives: 2014 BRZ Limited
Location: NJ
Posts: 82
Thanks: 5
Thanked 14 Times in 12 Posts
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quote:
Originally Posted by Boris_Petrov View Post
Does that mean that I can run 20 psi on 12.5 CR safely on 93?

Sent from my SM-A520F using Tapatalk
11 PSI is considered the upper of safe for stock CR.
elitegunslinger is offline   Reply With Quote
The Following User Says Thank You to elitegunslinger For This Useful Post:
Boris_Petrov (03-13-2019)
Old 03-13-2019, 04:59 PM   #7
Boris_Petrov
Member
 
Join Date: Dec 2018
Drives: 2013 GT 86
Location: BG
Posts: 23
Thanks: 21
Thanked 3 Times in 3 Posts
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quote:
Originally Posted by elitegunslinger View Post
11 PSI is considered the upper of safe for stock CR.
Yeah and that's about 93. What about 100 octane for example? Or water meth?

Sent from my SM-A520F using Tapatalk
Boris_Petrov is offline   Reply With Quote
Old 03-13-2019, 05:18 PM   #8
DarkPira7e
New Member
 
DarkPira7e's Avatar
 
Join Date: Feb 2017
Drives: 13 Firestorm Red FRS
Location: Burlington Vermont
Posts: 680
Thanks: 301
Thanked 453 Times in 265 Posts
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quote:
Originally Posted by Boris_Petrov View Post
What do you mean by dynamic compression?

Sent from my SM-A520F using Tapatalk
My use of it was essentially saying raising the compression with forced induction selectively, given the medium, chosen amount of boost, and tuning. So you could be a linear, or throw on a huge turbo, stuff all your torque into the final 2,000 rpm. The tuning of the engine with a higher static compression will limit this ability and essentially will just be raising power all over while you fight knock because of it.

Not that it can't be worked around, but it's easier to just go 10.0:1 CR with boost. If I wasn't using ' dynamic compression" accurately, I'm sorry.
DarkPira7e is offline   Reply With Quote
The Following User Says Thank You to DarkPira7e For This Useful Post:
Boris_Petrov (03-14-2019)
Old 03-14-2019, 11:39 AM   #9
gtengr
Senior Member
 
Join Date: Nov 2016
Drives: -
Location: USA
Posts: 602
Thanks: 303
Thanked 233 Times in 163 Posts
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quote:
Originally Posted by DarkPira7e View Post
My use of it was essentially saying raising the compression with forced induction selectively, given the medium, chosen amount of boost, and tuning. So you could be a linear, or throw on a huge turbo, stuff all your torque into the final 2,000 rpm. The tuning of the engine with a higher static compression will limit this ability and essentially will just be raising power all over while you fight knock because of it.

Not that it can't be worked around, but it's easier to just go 10.0:1 CR with boost. If I wasn't using ' dynamic compression" accurately, I'm sorry.
FI raises cylinder pressure rather than the compression ratio. The static and dynamic compression ratios are mechanical characteristics of the engine. Static compression assumes the cylinder is sealed for the entire compression stroke. But in reality, the cylinder isn't sealed until the intake valve is closed, and the dynamic compression ratio takes that intake valve closure timing into account.

Before variable cam timing became commonplace, static and dynamic compression had a direct correlation because cam timing was a fixed variable. But with variable intake cam timing, the dynamic ratio can be varied while keeping static compression constant. This is advantageous for engine building and tuning since you can use a higher static compression than you normally would, and then use cam timing to reduce the resulting dynamic compression in parts of the rev range where that high static compression would normally be problematic.
gtengr is offline   Reply With Quote
The Following 3 Users Say Thank You to gtengr For This Useful Post:
Boris_Petrov (03-14-2019), DarkPira7e (03-14-2019), tomm.brz (03-14-2019)
 
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

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

Similar Threads
Thread Thread Starter Forum Replies Last Post
Safe amount of boost on stock engine? Octane Forced Induction 51 12-06-2017 08:25 PM
Low compression build or boost sosick Engine, Exhaust, Transmission 3 02-17-2016 11:16 AM
compression+boost? subatoy Forced Induction 74 01-30-2015 05:32 PM
SOLD AEM Wideband Fail Safe AFR and Boost Gauge rb6freak Audio/Visual, Electronics, Infotainment, NAV 1 06-25-2014 10:59 AM
Gauges for Turbo, boost controller options? gdrider77 Forced Induction 27 05-13-2013 06:57 PM


All times are GMT -4. The time now is 02:15 PM.


Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Garage vBulletin Plugins by Drive Thru Online, Inc.