is 10.5:1 compression too high for a supercharger?

94' Cobra 351 · January 2nd, 2007, 05:13 PM

My mustang currently has 10.5 compression with 24lb injectors and i was wondering if that would work with a supercharger only running 8psi?

Darrell · January 2nd, 2007, 07:52 PM

Yes it is too much. How do you know it is 10.5:1? Are the pistons dished? If so what is the volume? What is the valve relief volume? Bore and stroke? Head gasket compressed thickness?

sleepinggt · January 26th, 2007, 08:08 PM

anything over about 9.5 is really too much to work well and ~8.5 or so is ideal

StangAddiction · January 26th, 2007, 09:02 PM

8.5:1 is considered ideal when running 91 octane fuel.

mdvaldosta · January 26th, 2007, 09:05 PM

With aluminum heads it's not the end of the world, though you'd have to pull alot of timing to run 8psi.

drgnracin72 · January 27th, 2007, 12:12 AM

9.5 is good for centrifugl blowers and and 8.5 is good for trin screw and turbos

94' Cobra 351 · January 27th, 2007, 09:58 AM

what if i just run really low boost? 4-5lbs? would that work or would it be a waste of the money to put on a turbo and run it so low. i am also considering stroking it to a 408 and starting off there. any advice with that?

Darrell · January 27th, 2007, 03:54 PM

Originally Posted by 94' Cobra 351

what if i just run really low boost? 4-5lbs? would that work or would it be a waste of the money to put on a turbo and run it so low. i am also considering stroking it to a 408 and starting off there. any advice with that?

You still haven't answered this:

Originally Posted by Darrell

Yes it is too much. How do you know it is 10.5:1? Are the pistons dished? If so what is the volume? What is the valve relief volume? Bore and stroke? Head gasket compressed thickness?

You might not have anywhere near 10.5:1. How do you know it is 10.5:1? What it says on the piston box doesn't mean anything. It is a general guestimate that is never correct.

94' Cobra 351 · January 28th, 2007, 06:01 PM

i never checked the compression myself, the guy i bought it from told me it was 10.5:1 so i took his word for it, he was VERY knowledgeable and knew his stuff. you can check it by getting a gauge that goes in the spark plug insert and hand cranking the engine right? right now i have the engine out because i am changing the rear main seal and the front seal and this thing is giving me hell,

Darrell · January 28th, 2007, 08:20 PM

Originally Posted by 94' Cobra 351

i never checked the compression myself, the guy i bought it from told me it was 10.5:1 so i took his word for it, he was VERY knowledgeable and knew his stuff. you can check it by getting a gauge that goes in the spark plug insert and hand cranking the engine right? right now i have the engine out because i am changing the rear main seal and the front seal and this thing is giving me hell,

The only way you can check it is by mathmatical calculation. There is no gauge that will tell you what the compression ratio is. My advice would be if you didn't physically check it yourself then don't assume it is what the guy told you no matter how knowledgeable he seems to be. I see alot of "knowledgeable people" that don't know how to accurately calculate compression ratios.

Trick Tuners · January 30th, 2007, 01:30 PM

It can work if you want to run 100+ octane.

Justincredible · January 30th, 2007, 02:16 PM

Originally Posted by Darrell

The only way you can check it is by mathmatical calculation. There is no gauge that will tell you what the compression ratio is. My advice would be if you didn't physically check it yourself then don't assume it is what the guy told you no matter how knowledgeable he seems to be. I see alot of "knowledgeable people" that don't know how to accurately calculate compression ratios.

+1

sleepinggt · February 3rd, 2007, 07:29 AM

Originally Posted by Jgorm

It can work if you want to run 100+ octane.

yea if you want to pay $10 a gallon go for the s/c lol

Darrell · February 3rd, 2007, 12:33 PM

Originally Posted by sleepinggt

Originally Posted by Jgorm

It can work if you want to run 100+ octane.

yea if you want to pay $10 a gallon go for the s/c lol

If you pay $10 a gallon for 100 octane I have a bridge to sell you....

I pay that for C16. 110 out of the pump goes for $3.50 to $4.00 every where I've seen it.

McMillin · February 4th, 2007, 12:53 PM

I built a new engine for my drag bike a couple years ago, I ordered all the parts new with 14 to 1 comp pistons. When I got done putting everything together I cc'd the combustion chamber. And the math told me I was at 11.55 to 1 so you just never know until your done. JM

sleepinggt · February 6th, 2007, 10:59 PM

down here in birmingham 100 out of the pump is 6.50 a gallon

93 is 2.30-2.50

drgnracin72 · February 7th, 2007, 03:10 PM

we have 101 out of the pump for 4.98 a gallon. 93 is about a .25 cents more than 91

94' Cobra 351 · February 7th, 2007, 04:12 PM

We just have 87, 89, and 93, each level up is 10 cents more.

87StangLX · November 3rd, 2007, 11:59 AM

Originally Posted by drgnracin72

9.5 is good for centrifugl blowers and and 8.5 is good for trin screw and turbos

how can i lower the compression on a stock engine? cuz i'm lookin into a KB 2.2 L kit for my 5.0

TurboLX · November 3rd, 2007, 05:25 PM

the compression on a stock 5.0 is about 9:1

you'll be fine

January 2nd, 2007, 05:13 PM	#1
94' Cobra 351 Regular Join Date: Dec 2006 Posts: 345	is 10.5:1 compression too high for a supercharger? My mustang currently has 10.5 compression with 24lb injectors and i was wondering if that would work with a supercharger only running 8psi?

January 2nd, 2007, 07:52 PM	#2
Darrell MM Ninjas! 1990 Mustang LX 9.36@143 mph Join Date: Jan 2006 Location: Fond du Lac, Wisconsin Posts: 5,789	Yes it is too much. How do you know it is 10.5:1? Are the pistons dished? If so what is the volume? What is the valve relief volume? Bore and stroke? Head gasket compressed thickness? __________________ Racing in memory of Dave Bandt 11/19/69 - 3/23/08 "he's traded his wheels for wings" Professor of Natural Aspiration Thanks to: Artie at Trick Flow and Harold at Furo Racecraft http://www.myspace.com/odarrellrules

January 30th, 2007, 01:30 PM	#11
Trick Tuners Authorized Vendor KB'd GT Join Date: Nov 2006 Location: San Diego Posts: 820	It can work if you want to run 100+ octane. __________________ SCT Custom Tuning, JLT intakes, Aeroforce Interceptor OBDII gauges and PLX wideband products @ Trick Tuners email joe@tricktuners.com PM for super MM member deals!

November 3rd, 2007, 05:25 PM	#20
TurboLX Site Moderator 1990 Mustang LX Turbo 8.67@165.91 mph Join Date: Oct 2006 Location: New York Posts: 8,221	the compression on a stock 5.0 is about 9:1 you'll be fine __________________ Wiring Diagrams, TSB's, OBD Service Codes and Engine Diagrams Available. PM For Info Myspace

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January 26th, 2007, 08:08 PM	#3
sleepinggt Regular Join Date: Dec 2006 Posts: 96	anything over about 9.5 is really too much to work well and ~8.5 or so is ideal

January 26th, 2007, 09:02 PM	#4
StangAddiction Enthusiast 2000 Mustang GT Join Date: Jan 2007 Location: Virginia Beach Posts: 869	8.5:1 is considered ideal when running 91 octane fuel.

January 26th, 2007, 09:05 PM	#5
mdvaldosta Maintenance Man 2002 Mustang GT 11.47@120.58 Join Date: Aug 2005 Location: Valdosta, GA Posts: 3,928	With aluminum heads it's not the end of the world, though you'd have to pull alot of timing to run 8psi.

January 27th, 2007, 09:58 AM	#7
94' Cobra 351 Regular Join Date: Dec 2006 Posts: 345	what if i just run really low boost? 4-5lbs? would that work or would it be a waste of the money to put on a turbo and run it so low. i am also considering stroking it to a 408 and starting off there. any advice with that?

January 28th, 2007, 06:01 PM	#9
94' Cobra 351 Regular Join Date: Dec 2006 Posts: 345	i never checked the compression myself, the guy i bought it from told me it was 10.5:1 so i took his word for it, he was VERY knowledgeable and knew his stuff. you can check it by getting a gauge that goes in the spark plug insert and hand cranking the engine right? right now i have the engine out because i am changing the rear main seal and the front seal and this thing is giving me hell,

February 4th, 2007, 12:53 PM	#15
McMillin Regular Join Date: Jan 2007 Location: oregon Posts: 96	I built a new engine for my drag bike a couple years ago, I ordered all the parts new with 14 to 1 comp pistons. When I got done putting everything together I cc'd the combustion chamber. And the math told me I was at 11.55 to 1 so you just never know until your done. JM

February 6th, 2007, 10:59 PM	#16
sleepinggt Regular Join Date: Dec 2006 Posts: 96	down here in birmingham 100 out of the pump is 6.50 a gallon 93 is 2.30-2.50

February 7th, 2007, 04:12 PM	#18
94' Cobra 351 Regular Join Date: Dec 2006 Posts: 345	We just have 87, 89, and 93, each level up is 10 cents more.

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