Trading compression for CFM
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TECH Junkie
Joined: Jan 2002
Posts: 3,015
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From: At the office
Trading compression for CFM I need to drop the compression ratio down the road for the future turbo upgrade. I'm liking TEA's 6.0L heads that flow 330+cfm/280+cfm through a stack @600 lift....vs. 306/26xcfm for my 5.3L heads
They flow about 20-25cfm better than what my current heads flow across the board.
The tradeoff for the extra cfm would be a drop in my compression from 10.8:1 to 9.0:1.
The heads would be on the car for a while before the Turbo got slapped on.
Any reason not to run these heads on a N/A 346 before the turbo goes on? What kind of hp/tq increase or decrease should I expect?
I'm debating on doing these heads sooner than later.
They flow about 20-25cfm better than what my current heads flow across the board.
The tradeoff for the extra cfm would be a drop in my compression from 10.8:1 to 9.0:1.
The heads would be on the car for a while before the Turbo got slapped on.
Any reason not to run these heads on a N/A 346 before the turbo goes on? What kind of hp/tq increase or decrease should I expect?
I'm debating on doing these heads sooner than later.
Re: Trading compression for CFM You will definitely lose torque. Not only from the compression drop, but also from the increased port volume. The loss in torque will also be accompanied buy a raising of the rpm at which you see peak torque, and an overall narrowing of the power band.
Why the rush to switch? What is your time-line for the turbo swap? If it's something you're going to be doing in the very near future, then maybe the switch would be warranted, otherwise, I would wait until this next winter, and then sell your heads, buy the 6.0's, do your short-block and add the turbo and associated fuel system upgrades.
In the mean time, you could start purchasing all the assorted pieces you're going to be needing, so that when the time comes, you can make the move all at once.
Just my $.02
Why the rush to switch? What is your time-line for the turbo swap? If it's something you're going to be doing in the very near future, then maybe the switch would be warranted, otherwise, I would wait until this next winter, and then sell your heads, buy the 6.0's, do your short-block and add the turbo and associated fuel system upgrades.
In the mean time, you could start purchasing all the assorted pieces you're going to be needing, so that when the time comes, you can make the move all at once.
Just my $.02
TECH Fanatic
Joined: Aug 2002
Posts: 1,566
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From: Objects in mirror no longer matter.
Re: Trading compression for CFM You might as well wait and enjoy the current setup. Even if the topend power is there, the responsiveness and lowend power of a lower compression head will not be fun.
Re: Trading compression for CFM General rule of thumb is that each full point of compression is worth ~4% (up or down).
As Hitman mentioned, your car would be VERY sluggish with the drop in compression; the cylinder pressure that your cam was designed to work with would be off; additionally, expect a MUCH mushier throttle due to the compression drop.
As Hitman mentioned, your car would be VERY sluggish with the drop in compression; the cylinder pressure that your cam was designed to work with would be off; additionally, expect a MUCH mushier throttle due to the compression drop.
