Compression increase change!!!

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Apr 17, 2007 | 02:36 PM

Pearlwhite94

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Compression increase change!!!

ok i have a 94 f150 with the 300, i was talking to a friend who knows about compression and turboed engines. We both looked up te compression ration of the 300 motor and thought their was alot of room for improvement. our idea was to remove the heads and take them to a machine shop that can machine them a bit to increase the cylinder compression. i realised that i will have to use higher octane gas which is not a problem since i already use it. I need to know some numbers though, what would be the ideal compression ratio to shoot for? is this a good idea at all? what type of power increase can i hope to achieve? thanks for the help form all the 300 experts out there!!!

Apr 18, 2007 | 01:56 PM

Silver Streak

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From: Broken Arrow, OK

IIRC, you can usually expect about a 2% gain for every point of compression you add. To add a point of compression you have to remove about 15cc of compressed volume. Is it really worth it to gain 3 hp for a few hundred bucks? On the other hand, it might gain you a noticable amount of throttle response and should help the mileage a bit.

Compression is like boring or stroking, it just isn't worth it except in a few special cases.

Apr 19, 2007 | 09:01 AM

NavyMIDN08

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if you really wanted more compression, you'd probably be better off with new, flattop or slightly domed pistons (check clearance!!!) with new rings. if you bump the compression on old rings, you'll really risk blowing the rings, or you'll have excessive blowby. and, its going to be about the same price. figure the price of the headwork, plus gaskets and everything, and it'll be about the same price

i agree with silver streak however, if you're bumping just to bump, then its probably not going to give you the results you're looking for.

Apr 19, 2007 | 12:05 PM

srercrcr

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Higher gas mileage with higher compression? Not where I come from.

Apr 19, 2007 | 01:39 PM

Silver Streak

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From: Broken Arrow, OK

Where are you from? Mars? Anything you do that increases efficiency without drastically changing the rpm range the engine runs in will help mileage. The problem with adding mods is that the driver usually has his foot on the floor constantly after adding them and the mileage goes to hell. The ONLY variable in the thermal efficiency equation for an Otto cycle engine is the compression ratio. The higher it is, the higher the thermal efficiency.

Apr 19, 2007 | 09:55 PM

Pearlwhite94

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Well i guess it wouldnt really be worth it then. but u have to agree that the stock compression on that engine sux! and it kills me that i have a five liter six cylinder with 145 hp at best. and its true that mods help the mileage but what kills it is the driving habits of the owner. like mine! my engine is at full open throttle 70% of the time im driving it!! i wish it was faster though. im planning on getting a full exhaust and an intake, maybe megasquirt and nos! sumday!