Street Engine Compression Ratio??

-
B

Blucuda413

Well-Known Member
Joined
May 20, 2012
Messages
194
Reaction score
154
Location
Alexandria, Louisiana
Planning on building a 360 street engine with a Procharger. Heads will be ported stock units with a blower cam which is probably bigger than I need. Probably will go with either a blo-thru carb or might even try a Holley FI unit. Basically I'm looking for a recommended compression ratio so I can buy pistons and rods. Thanks, Max
 
I would get the static compression as low as I could and spin hell out of the blower. Never made any sense to me why guys build a high static compression blower motor and then under drive the blower. Work that puppy. That's why you bought it.
 
RustyRatRod said:
I would get the static compression as low as I could and spin hell out of the blower. Never made any sense to me why guys build a high static compression blower motor and then under drive the blower. Work that puppy. That's why you bought it.
Click to expand...

Because you can build a 10-1 or a 11-1 engine, work the blower to death and still run pump gas in many cases. Ignition timing comes into play and fixes everything except exceeding pump gas limits inside the engine. If that happens, back off the blower pressure.
 
RustyRatRod said:
I would get the static compression as low as I could and spin hell out of the blower. Never made any sense to me why guys build a high static compression blower motor and then under drive the blower. Work that puppy. That's why you bought it.
Click to expand...
X2 as low as you can, this one I put together has 7.5 compression, I went out of my way to keep is low, did everything I could to dump the compression.

pknkdU.jpg
 
rumblefish360 said:
Because you can build a 10-1 or a 11-1 engine, work the blower to death and still run pump gas in many cases. Ignition timing comes into play and fixes everything except exceeding pump gas limits inside the engine. If that happens, back off the blower pressure.
Click to expand...

I prefer to build them the way I stated, because then there's no need to back off timing and lose power. A boost retard is advised anyway, so the higher the static compression, the more timing retard would come into play. I've always thought about some kind of variable belt drive or some such that could vary the speed of the blower in live operation. There are some turbochargers out now for instance that vary the pitch of the vanes on the compressor side of the turbo to get them to spool up very quickly.
 
RustyRatRod said:
I prefer to build them the way I stated, because then there's no need to back off timing and lose power. A boost retard is advised anyway, so the higher the static compression, the more timing retard would come into play. I've always thought about some kind of variable belt drive or some such that could vary the speed of the blower in live operation. There are some turbochargers out now for instance that vary the pitch of the vanes on the compressor side of the turbo to get them to spool up very quickly.
Click to expand...
In the end, pressure is pressure in the engine. If you start with a low compression 7.0-1 engine, your just spinning the blower harder to get the same pressure as the 10-1 engine. Timing will have to be retarded the same for both engines at the same cylinder pressure.
 
Sorry slow getting back still cleaning up storm debris. To add additional info I have everything to build this engine except pistons/rods and blow thru carb. I do not plan on using an intercooler, going to be simple easy build. Cam: unknown brand believed to be old Comp but they cannot verify. Believe it to be 300/300 advertised, lift .585/.585 on a 114LSA, it may have 6 degrees ground in. The pump gas here is either 91 or 93, nothing else available except aviation fuel which I've never used.
Lots of info here[/QUOTE]
 
This is a loaded question really. We need the intended use of the car. The reason to keep some compression in the engine and not run as much boost is to keep the charge temp cooler. “Pressure is not just pressure” in the combustion chamber. There are many factors at play. Spinning the blower harder and harder has a rate of diminishing returns. The harder you spin the blower the more heat it makes and and power goes away quickly. So, for a street car the best choice is always a compromise. Run a nice static compression of around 9:1 and keep the engine snappy when out of boost, and not terribly high to run into problems with chamber temp and detonation when in boost on pump gas. As said timing is always super critical. So is fuel selection. The fuel selection dictates timing and the amount of power you can potentially make.
 
With a blow through you don’t always need an intercooler with moderate boost levels but when you start turning up the boost (you will trust me) on pump gas you’re shooting yourself in the foot by not using one. It’s one of the simplest parts to install on a car and it’s free horsepower. I ALWAYS recommend an air to air intercooler on a street car on pump gas.
 
Car will not be a daily driver Probably periodically driven and to local shows when possible. I decided to go with the Procharger to keep it stock looking as much as possible. I have a 6-71 setup but I wouldn't feel comfortable with that bulk sticking thru the hood.
 
Prochargers are great and capable of lots of power. I have a friend with a 363 small block ford procharged and he’s making near 1400 hp.
11E35E3D-4239-4032-8D56-2B80A3B2FBC3.jpeg
 
Yea the car runs hard. He’s been in the 5.60s and is building a bigger inch small block shooting for 1600.
 
You must log in or register to reply here.
-

Back
Top