Is greater then 9.5:1 good? Is between 9.6:1 and 9.8:1 ideal for pump gases and power?

I estimate between 9.6:1 and 9.8:1 compression ratio for my engine ( I haven't measure and cc'd the heads yet).

How much do good shops charge to angle mill heads usually?

This is for:
ZZ4 cam
TFS 23* heads
Accel intake/runners
free flow exhaust

James

 

Can run up to 11:1 compression with aluminum... More compression=more power

 

You can run a point higher compression with aluminum heads because of their thermal conductivity they run cooler. But it all comes down to combustion chamber design, a good combustion chamber allows less timing advance and more compression a poor chamber design means more ignition advance and less compression or you will get detonation. It depends on the heads, personally I wouldn't go over 10.5:1 just to be safe, unless you have some very good heads and polish the combustion chambers and blend the tops of the pistons.

 

I'm running 10.2 to 1 with TFS Twisted Wedge.
bsa

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"If they do not run, Then they will die." - Stonewall Jackson
#3
'87 IROC, 355 TPI, Converted to SD, 700R4, B&M Megashifter, 3.42, Trick Flow Twisted Wedge Heads, Edelbrock Intake, Accel Runners, Comp Cam, Crane Gold rockers, Lucas 23# injectors, Edelbrock headers, Flowmaster 3'' exhaust, Mallory Ignition, Transgo Performance Shift Kit, Corvette Servo, 2,000 Stall Torque Converter

 

James,

Compression ratio is a measure of mechanical compression, and can affect power and economy. Compression pressure is more important, because it is not a theoretical number but an actual measurement. An engine with a lower compression ratio and a well designed cam can actually achieve higher compression (pressure) than an 11:1 engine with a mismatched cam profile.

You need to do some more investigation before deciding what specs to build toward.

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Later,
Vader
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"What a Day..."
Adobe Acrobat Reader

 

OK, I know the difference bwtween the static/mechanical compression ratio and the dynamics and effiencies invloved in the real compression ratio. I don't think there is a practical way to measure the dynamic compression ratio. Using mass rates of air isn't going to get you what you want and I'm not going to drill a pressure sensor into my combustion chamber to find out. And I'm not going to buy/write the fluid dynamics software to determine the number. But as a general concensus, what is a good compression ratio for use with aluminum heads?

I see that the fastburn 385 (hp) has a CR of 9.6:1 and edelbrock 's engines have a CR of 9.5:1, while OEM aluminum headed engines are more like 10.0+:1. Being an ME I don't need to be reminded of the otto cycles efficiency and relationship with compression ratio or the carnot cycle. I'm just asking for a general number.


James

 

I wouldnt even think of running less than 10:1 with aluminum heads, thats like throwing power away. I have 10.3:1 on one car and it could easily run more than that, it will run on 87 and not detonate on most days.

 

I agree with max. In the 10's sounds good for pump gas and power...

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89 IROC-Z 350 TPI

-Flowmaster Catback
-Performance Resource Chip
-700R4 (Rebuilt) Too much done to actually list
-K&N Airfilters
-Ported Plenum
-2.77 Gears (not much to brag about but eh, its there)
-MSD 8.5 mm plug wires
-Gutted cat
-!AIR
-Gutted Air Boxes

 

What thermostat temp are you guys w/ aluminum heads running? I know from my boating friends that you won't get good results using aluminum heads and a 160 stat. They usually had to bump it up near 190~200+ depending on the water conditions.


James

 

My frineds Brodix stage II heads are alluminum and he runs 14 to 1 compression. Still runs fine till this day. He of course just races is weekends, not a daily driver.

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92' camaro
New 305 block TPI conversion, Flat top pistons,Bore over .30 Forged parts all around,Edelbrock intake,ported plennum,ported corvette alluminum heads, accel cam,52mm throttle bodie, SLP runners Home aid cold air induction, Air foil,ford SVO 19lb injectors,fuel regulator,cloys timing chain, comp alluminum roller rocker arms and pushrods MSD 8.5 mm wires, bosch plattinum plugs, hypertech cap & rotor and coil, Edelbrock TES headers, free flowing catalytic converter and a 3 inch force II flowmaster exhaust system, and a 3 inch cutout,Zoom multi friction clutch, T-5 tranny,billenstien shocks&struts.
Soon to come!!!
Procharger system 12lbs o boost.
New paint job(hawaiin orchid purple)Cast alluminum ZR1 rims w/ 275 tires.
Favorite quote: "where ever u go, there u are"

Other car;
1971 plymouth Duster
Mods:340,edelbrock victor jr. intake, 650 4 barrel holley, heddman headers,40 series dual flowmasters, cold air intake,4:10 gears, just got a new paint job and cragar rims with 315 tires in the back.
:Yeah its not a chevy but damn how many 71' dusters have u seen in the streets.

 

I run a 180, the car runs around 185-190 most of the time.

 

I run a 160º thermostat in mine, 10.3:1 compression, and the engine runs nice and cool.

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West Coast GM Shootout 2001!
1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.23 @ 107.62 MPH
Southern California
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