IPD sale XeMODeX - Experts in Volvo Electronics
Did you know? 🤔
Logged in users can get email notification of topic replies Log in or register (free).
Amazon Link Buy anything with this and it helps MVS!

Safe Boost Limits By Engine Chart

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70

User avatar
Posts: 372
Joined: Mon Jun 30, 2014 5:25 pm
Year and Model: 1995 850
Location: St. Louis Missouri
Has thanked: 16 times
Been thanked: 34 times
United States of America

Volvo Repair Database Safe Boost Limits By Engine Chart

Post by callahanoffroad » Mon Jul 08, 2019 7:26 am

Hello friends!

I was pondering what the safe turbo boost limits for each model were and it lead me to doing a little bit of math on everyone's behalf so that you can have an actual reference chart to go by.

I have calculated the Effective Compression Ratio (ECR) of the three available P80 Volvo Engines: 2.4L Naturally Aspirated, 2.4L Low Pressure Turbo, and 2.3L High Pressure Turbo. These numbers would be correct for any 5 cylinder Volvo engine.

This chart does not take into account tuning tricks like running lean to heat the mixture or running rich to cool the mixture. The optimum turbo efficiency or turbo heat output. It is just a general chart for quick reference.

If you'd like to do your own math here is the formula:

Square Root of: ((Boost Pressure in LBS + 14.7) / 14.7) * Compression Ratio = ECR

The Max Safe ECR for US Gas is as Follows:

91 Octane 12.1:1
93 Octane 12.5:1

2.4L Naturally Aspirated Turbo
Before I begin this one, I do want to say that it is mathematically possible to turbocharge a N/A car using a LPT setup.
Stock Piston Compression Ratio and ECR = 10.5:1

4lbs of Boost = 11.84 ECR
5lbs of Boost = 12.15 ECR
6lbs of Boost = 12.46 ECR
7lbs of Boost = 12.75 ECR (not safe without tuning)

2.4L Low Pressure Turbo
Stock Piston Compression Ratio = 9.0:1
Stock Boost = 6 psi
Stock ECR = 10.67
8lbs of Boost = 11.19 ECR
10lbs of Boost = 11.66 ECR
12lbs of Boost = 12.13 ECR
13lbs of Boost = 12.36 ECR
14lbs of Boost = 12.58 ECR (borderline unsafe/unsafe without tuning)

2.3L High Pressure Turbo/T5/R
Stock Piston Compression Ratio = 8.5:1
Stock Boost = 9.7lbs
Stock ECR = 11.33:1

12lbs = 11.45 ECR
13lbs = 11.67 ECR
14lbs = 11.87 ECR
15lbs = 12.09 ECR
16lbs = 12.29 ECR
17lbs = 12.48 ECR
18lbs = 12.68 ECR (not safe without tuning)

These are purely mathematical figures they assume a 14.7:1 air fuel ratio and as I stated before do not take into consideration temperature, altitude, superior intercooling, lower operating temperature, tuning for a rich environment to lower detonation temperatures, timing tricks, etc. Another interesting aspect that I have not calculated here is Effective Dynamic Compression Ratio, which can actually lower these numbers significantly. But again this is a really good back of the hand chart to go by. :D

What's most interesting is the definitive proof that lower compression ratio motors can handle extra boost and will inherently make more power at the higher boost levels as a result. Hope this helps anyone who is wondering how much boost they can safely run in their motor!
These users thanked the author callahanoffroad for the post (total 6):
Author, Chef, and Shade Tree Mechanic

1995 Volvo 850, Non-Turbo, VVIS, LH FI, Green, 215,000 miles. B5254FS engine. Herman. viewtopic.php?f=1&t=84393

1996 Volvo 850, died at 280,000

Founder of: CookingForChemo.Org

User avatar
Posts: 9677
Joined: Sat Jul 25, 2009 2:03 pm
Year and Model: 850, S/V70, 06 S60R
Location: Iowa
Has thanked: 95 times
Been thanked: 279 times
United States of America

Re: Safe Boost Limits By Engine Chart

Post by erikv11 » Thu Jul 18, 2019 9:34 am

This is why several years ago I dropped T5 tune-injectors-turbo into my V70 GLT (contains 2.4 LPT engine from the factory)!
'95 854 T5-R, Motronic 4.4, 185k
'96 855 NA, 145k
'98 S70 NA, 220k (living out west)
'98 V70, T5 tune-injectors-turbo, LPT engine, 286k
'06 S60 R, 167k
'99 Camry V6 :shock: 125k
gone: '96 NA 850 210k, '98 NA V70 182k

User avatar
Posts: 3966
Joined: Tue Dec 30, 2014 10:45 am
Year and Model: 2K V70R M56
Location: Charlotte, NC
Has thanked: 44 times
Been thanked: 154 times
United States of America

Re: Safe Boost Limits By Engine Chart

Post by bmdubya1198 » Thu Jul 18, 2019 4:37 pm

Great info here. I'm still thinking about boosting my S90. More so now that I know it runs and drive as well as it does...
2000 V70R Venetian Red/Charcoal M56 Swapped 195k
2003 S60 2.4T Silver/Black 112k
2007 XC90 V8 AWD Sport Titanium Grey/Black 166k
1991 944 Turbo Dark Green/Beige 173k
1992 245 Base White/Beige 249k
2006 BMW 330i
1999 BMW 528i
2000 S70 GLT Mystic Silver/Taupe 253k
1993 944 Base Beige/Beige 221k
1998 V70 GLT Black/Beige 199k
1998 S90- Silver/Gray 207k
1995 850 GLT Tropic Green... crushed
2001 S60 2.4T Black/Black 230k
1988 744 Turbo M46 Beige Metallic/Beige 188k

Post Reply
  • Similar Topics
    Last post