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Author
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Topic: How Much HP increase going from 8 1/2.1 to 10.1 comp ratio?
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Glenn
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Member # 520
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posted
 
 
My car is at 8 1/2.1 I am thinking about milling my heads, how much HP increase would I see?
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S-Trim,331,H/C/I
"JohnB groupie train"
My Car
DragGuam
Posts: 2009 | From: Stationed on a Pacific Island, Guam | Registered: Oct 2001
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JohnB
Tech Moderator
Member # 969
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posted
You won't be able to mill them enough to make 10...MAYBE 9.
Keep in mind, when you mill the heads, you also bring the valves closer to the pistons..and you're on the edge right now what your current camshaft.
No need to tear the engine down...just add a supercharger!! ![[Big Grin]](biggrin.gif)
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1965 Shelby Cobra
1993 Cobra
2012 F150 Raptor
2020 GT500
Posts: 6523 | From: Orlando FL/Redding CA | Registered: Mar 2002
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JoeT
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Member # 298
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posted
I thought the rule of thumb was ~ 10 HP for every full point at aroud our level (300) some cams really love compression though, so it could be a little more. I'd say as much as 20, in your case for another 1.5 full points.
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1984 Ford Tempo AOD--- RIP
Posts: 6785 | From: San Jose | Registered: Jun 2001
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66 AC COBRA
Nitrous King
Member # 904
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posted
u mill the heads then u have to screw with intake alignment, have to get the heads milled some where, take the heads off ur car, spend money on gaskets, etc etc
or u can either toss a charger, turbo, or nitrous on, turbo being expensive, nitrous cheap from me , or the middle priced charger, either way is taken ur heads off to gave 15hp worth it, while there off my as well port them to, and port the intake
the car runs great right now i assume, so leave it alone and either behappy with it or a power adder is one or a few paychecks away ![[patriot]](graemlins/patriot.gif)
[ September 24, 2003, 12:59 PM: Message edited by: 66 AC COBRA of CA PERFORMANCE ]
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FFR AC Cobra
72 Vega - WCHRA Extreme 10.5
Posts: 6280 | From: Winters | Registered: Feb 2002
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Jeff S
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Member # 371
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posted
Why did you build an 8.5:1 motor? Were you planning on a blower?
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'90 Mustang LX: 8.53 @ 157.92 w/ 1.33 60' on DR's
'10 ZR1: FOR SALE
'14 E63 S: RENNtech ECU
'04 Gallardo: UGR TTG
Posts: 2121 | From: San Jose, CA | Registered: Aug 2001
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Glenn
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Member # 520
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posted
quote:
Originally posted by Jeff S:
Why did you build an 8.5:1 motor? Were you planning on a blower?
yeah, but also heard that I can add bout 8psi to a 10:1, just trying to make as much HP as I can.
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S-Trim,331,H/C/I
"JohnB groupie train"
My Car
DragGuam
Posts: 2009 | From: Stationed on a Pacific Island, Guam | Registered: Oct 2001
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Glenn
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Member # 520
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posted
quote:
Originally posted by JohnB:
You won't be able to mill them enough to make 10...MAYBE 9.
Keep in mind, when you mill the heads, you also bring the valves closer to the pistons..and you're on the edge right now what your current camshaft.
No need to tear the engine down...just add a supercharger!!
might be swapping out the cam.
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S-Trim,331,H/C/I
"JohnB groupie train"
My Car
DragGuam
Posts: 2009 | From: Stationed on a Pacific Island, Guam | Registered: Oct 2001
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Saint
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Member # 2746
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posted
im running 8 psi on my motor with stock compession
Posts: 239 | From: Antioch | Registered: Apr 2003
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Jeff S
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Member # 371
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posted
quote:
Originally posted by Glenn:
quote:
Originally posted by Jeff S:
Why did you build an 8.5:1 motor? Were you planning on a blower?
yeah, but also heard that I can add bout 8psi to a 10:1, just trying to make as much HP as I can.
I'd guess you will make more power with 8psi and 8.5:1 compression then you will with 8psi and 10:1 compression on 91 octane. It will also be much less prone to detonation.
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'90 Mustang LX: 8.53 @ 157.92 w/ 1.33 60' on DR's
'10 ZR1: FOR SALE
'14 E63 S: RENNtech ECU
'04 Gallardo: UGR TTG
Posts: 2121 | From: San Jose, CA | Registered: Aug 2001
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93PONY
Mr. Valve Events
Member # 60
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posted
How much power did this thing put out?
With higher compression comes more power accross the board & more throttle response. With lower compression motors I use more overlap to compensate for the lack of compression. But it seems you're limited in cam due to the pistons. That puts a damper on things....
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www.advancedenginedevelopment.com
SCT dealer
Dynotuning
(916)715-7569
Posts: 4265 | From: Fair Oaks, CA | Registered: Nov 2000
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91 5.0
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Member # 1527
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posted
quote:
Originally posted by Glenn:
quote:
Originally posted by Jeff S:
Why did you build an 8.5:1 motor? Were you planning on a blower?
yeah, but also heard that I can add bout 8psi to a 10:1, just trying to make as much HP as I can.
Yeah, but now you can run more boost. You'll get way more power with the lower compression and increased boost. Stick with the lower compression. Just my .02 cents.
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02 GT - Zinc Yellow
91 5.0 LX - Red
Posts: 1316 | From: Fairfield | Registered: Jul 2002
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93PONY
Mr. Valve Events
Member # 60
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posted
quote:
Originally posted by 91 5.0:
quote:
Originally posted by Glenn:
quote:
Originally posted by Jeff S:
Why did you build an 8.5:1 motor? Were you planning on a blower?
yeah, but also heard that I can add bout 8psi to a 10:1, just trying to make as much HP as I can.
Yeah, but now you can run more boost. You'll get way more power with the lower compression and increased boost. Stick with the lower compression. Just my .02 cents.
To expand a little on this.....
The larger your combustion chamber, the more air you can pack in. If you plan on running a total of say 16 to 1 compression (calculated WITH boost), you'll get more power out of a larger chamber. A larger chamber volume at 8psi will make more power then a smaller chamber volume at 8psi....more then what upping the compression ratio will add.
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www.advancedenginedevelopment.com
SCT dealer
Dynotuning
(916)715-7569
Posts: 4265 | From: Fair Oaks, CA | Registered: Nov 2000
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Gear Head
JARED
Member # 779
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posted
quote:
Originally posted by 93PONY:
quote:
Originally posted by 91 5.0:
quote:
Originally posted by Glenn:
quote:
Originally posted by Jeff S:
Why did you build an 8.5:1 motor? Were you planning on a blower?
yeah, but also heard that I can add bout 8psi to a 10:1, just trying to make as much HP as I can.
Yeah, but now you can run more boost. You'll get way more power with the lower compression and increased boost. Stick with the lower compression. Just my .02 cents.
To expand a little on this.....
The larger your combustion chamber, the more air you can pack in. If you plan on running a total of say 16 to 1 compression (calculated WITH boost), you'll get more power out of a larger chamber. A larger chamber volume at 8psi will make more power then a smaller chamber volume at 8psi....more then what upping the compression ratio will add.
So your saying a car with lower compression with the same amount of boost will make more than a car with higher compression at the same exact psi?
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Support our troops!
Posts: 5685 | From: EASTBAY | Registered: Jan 2002
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93PONY
Mr. Valve Events
Member # 60
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posted
Depends on the application....
Glen is looking at a 15-20RWHP increase N/A from going from 8.5 to 10.0 to one compression. First off he'd have to take out 14cc's somewhere to get this...this would mean milling off .084 inches off the heads...which isn't gonna happen. LOL
But, if he were to take out 14cc's from the combustion chamber this would give him 10 to 1 compression.
There is roughly 7cc's in the head gasket itself. Total chamber volume for 10 to 1 compression on a 306 is ~68cc's. With 8.5 to 1 compression it's 82cc's. That's a 17% difference.
Total compression being the same on both applications (total meaning with boost) you're looking at an increase in power of basically 17%.
But...it would take more boost to get the 8.5 to one compression motor to make the same 'effective compression' as the 10 to one motor.
By how much you say???
Well...lets see....
A 10 to 1 compression motor with 8psi has an effective compression of 15.5. Anything under ~16 is okay for use with pump gas.
An 8.5 to 1 compression motor needs 12psi boost to make the same 15.5 effective compression.
Now...that's 4psi more...to make the same 'effective compression' & due to the larger chamber volume this will make ~17% more power then the 10 to 1 compression motor.
But you may say that more boost = more heat! Ah yes...it does. But think of it this way..... Typically blowers will have intercoolers to cool the air before entering the motor. So, on one motor the air is compressed to 8psi, cooled a little, then compressed again to 10 to 1 by the pistons, which creates a LOT of heat & gives us 15.5 effective compression. The other motor is pushing 12psi that is cooled off before being compressed 8.5 to 1. This will also give 15.5 to one effective compression...but the air-charge will be a few degrees cooler due to more air being cooled by the intercooler & not being compressed by the pistons so much.
Ah...but what about 2 motor pushing the same boost one with 8.5 compression & one with 10. Well...it's a toss up. One is making 15.5 effective compression with a 68cc chamber, the other 13.2 effective compression (15% less) with an 82cc chamber (17% more). Basically it comes down to heat in the aircharge & compressor effeciency as to which combo would make more power. For sure, the higher compression motor would have snappier throttle response & rev faster when not in boost. But peak power output....it's a toss up IMO. But, I'd go for the cooler aircharge.
[ September 24, 2003, 05:17 PM: Message edited by: 93PONY ]
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www.advancedenginedevelopment.com
SCT dealer
Dynotuning
(916)715-7569
Posts: 4265 | From: Fair Oaks, CA | Registered: Nov 2000
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166 Merlo
FELONY
MOTORSPORTS
Member # 1549
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posted
Baaaahhhhhhhhhhh! Put it on the dyno. ![[Cool]](cool.gif)
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'89 - Boss Coupe
'70 - Drop Cutthang
'68 - Cougnut
'87 - 0166, Its real
Posts: 3953 | From: Thebay | Registered: Jul 2002
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Glenn
¯
Member # 520
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posted
BOOST IT IS!!!
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S-Trim,331,H/C/I
"JohnB groupie train"
My Car
DragGuam
Posts: 2009 | From: Stationed on a Pacific Island, Guam | Registered: Oct 2001
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91 5.0
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Member # 1527
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posted
quote:
Originally posted by Glenn:
BOOST IT IS!!!
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02 GT - Zinc Yellow
91 5.0 LX - Red
Posts: 1316 | From: Fairfield | Registered: Jul 2002
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Red97SVT
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Member # 2811
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posted
Less compression will allow you to run more timing with a given amount of boost or more boost with the same timing with out detonation. More timing or more boost = more power. Take your pick!
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Engine: HCI forged 0.30' over N/A.
Suspension: Full Griggs by Apex.
Drive train: T-56, Auburn pro, 31 spline axles, 3.73s.
Posts: 246 | From: Manteca | Registered: May 2003
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