IPD sale Volvo Parts
Did you know? 🤔
Logged in users can get email notification of topic replies Log in or register (free).
Amazon Link Buy your stuff using 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
callahanoffroad
Posts: 243
Joined: Mon Jun 30, 2014 5:25 pm
Year and Model: 1995 850
Location: St. Louis Missouri
Has thanked: 16 times
Been thanked: 21 times
United States of America
callahanoffroad

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 5):
Clemensjreedmatthew1Peevarinoerikv11


Author, Chef, and Shade Tree Mechanic

1995 Volvo 850, Non-Turbo, VVIS, LH FI, Green, 215,000 miles. Herman. https://www.matthewsvolvosite.com/forum ... =1&t=84393

1996 Volvo 850, died at 280,000

Founder of: CookingForChemo.Org

User avatar
erikv11
Posts: 9031
Joined: Sat Jul 25, 2009 2:03 pm
Year and Model: 850, S/V70, 06 S60R
Location: Iowa
Has thanked: 54 times
Been thanked: 178 times
United States of America
erikv11

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, 140k
'98 S70 NA, 210k (living out west)
'98 V70, T5 tune-injectors-turbo, LPT engine, 280k
'06 S60 R, 160k
gone: '96 NA 850 210k, '98 NA V70 182k

User avatar
bmdubya1198
Posts: 2958
Joined: Tue Dec 30, 2014 10:45 am
Year and Model: '98 V70 GLT
Location: Charlotte, NC
Has thanked: 27 times
Been thanked: 77 times
United States of America
bmdubya1198

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...


1998 V70 GLT Black/Beige 193k
2000 V70R Venetian Red/Charcoal M56 Swapped 188k
2001 S60 2.4T Black/Black 230k
2007 XC90 V8 AWD Sport Titanium Grey/Black 155k
1998 S90- Silver/Gray 207k
1995 850 collection of parts... crushed... still have parts, PM if interested!
1988 744 Turbo M46 Beige Metallic/Beige 188k- Still kicking myself for getting rid of this one

Post Reply