I was watching that Trucks show on Spike television and the host said that puting a turbo or super charger on a high compression engine sorta defeats the purpose. So it'd be a bad idea to put either on a 302 with a compression ratio of 10.7:1, 10.2:1 or 9.8:1?

 

with gasoline, it does defeat the purpose to some degree.

You can do it, and run a few lbs of boost, and you will feel some increase in power. Ford lightenings with the supercharger, a lot of FWD buicks, etc, are 9:1 or higher with a blower of some kind.

But for what you will spend on supercharging, what you will get out of it I don't think is worth the effort and cash involved, for an engine with that high compression.

Thats why I'm building my 500cid stroker to 7:1 or thereabouts, what power I lose with compression is made up with significantly higher boost.

Couple years ago I (and several friends) did some Buick 4.1 V6 experiments. Different c/r's, different amounts of boost, sitting on an engine dyno. We ran all the engines until they blew up, on purpose.

The concensus after the "event" was running a 6:1 c/r with 36-38lbs of boost produced the most power in the mid-range RPM, which is what you generally use on the highway. You're not at 900 RPM at 70mph, nor should you be at 8000 RPM at that speed, unless you forget to shift

But what you build depends on what your purpose is. The way you'd build a 1/4 strip engine is very different from a daily driver, a tow vehicle, a mud-play truck, or a puller for competition.

And that actually is the hard part, deciding what you're building for. Unfortunately all engines are about tradeoffs... rarely can you have ridiculous low-end torque and tremendous high-RPM performance. You can balance to the two, yes, but like everything else its a huge list of tradeoffs.

 

Sure you can boost a high compression engine. The trick is to keep it from pinging and destroying your engine, which if your compression ratio is high enough, will be next to impossible.

 

Boost friendly compression ratio for a street driven vehicle is around 8.4 - 9.0:1. Lightnings run 8.4:1 and can take about 15 psi on pump gas. My truck is 9.1:1 and I'm seeing around 10 psi max before the shift with no pinging at all. Compression ratio is important as well as intake charge temperatures....i.e. intercoolers will allow the use of more boost before running into problems.

 

Intercoolers will also provide much more power, and greater duralbility. Its a win-win.
I don't agree that putting a turbo/super charger on a vehicle with a high comp. ratio defeats the purpose, yes you may not be able to run quite as high boost, therefore ultimate power will probably be reduced, so your top speed at Nardo may suffer However, drivability will be increased you will get reduced turbo lag like frederic said it is up to how you are setting the truck up. Personally I would still run reasonably high compression so throttle response is far quicker, and sacrifice my quarter mile time, but thats just my opinion...

 

If you want throttle response... you can also run a smaller turbo, which will spool up a little faster than a bigger turbo. Again, it depends what RPM range you're building for. If your high torque 500cid turbo motor is going to hit 8000 RPM, then thats a different turbo selection than if your 500cid turbo motor maxes out around 4500 RPM.

For my crewcab, based on how its geared, 8000 RPM would just cost more in hard parts, make a lot of noise, and not provide any fun at the lower RPMs which one uses on the street.

Intercooling is an interesting subject to debate.

Air to air intercooling is generally better for vehicles that have tremendous airflow, such as high speed, long distance type of cars. For short bursts of power, its not necessary the best option because the aluminum intercoolers often get heat-soaked, and turn into an "interheater". Size of the turbos, its location, and its size determines how useful it can be as well.

Water to air intercooling is probably the best choice for 1/4 mile times... replace the cold water after every run, as water takes in more heat than air alone.

My favorite for 1/4 runs is the dry ice method. The airbox is replaced with an igloo cooler with two 3" or 4" holes, one either side, and you toss in a chunk of dry ice

There is probably 20 other ways of doing this too. Run some A/C lines through an insulated box, that contains water. Run the A/C compressor and the water cools down fairly quickly. Then for your quick 1/4 or light to light run, shut off the AC and boil the water over on the run. Then turn on the AC and the water is recooled.

Another fun option is to skip the intercooler completely, and drill a pinhole or two in one of the post-turbo pipes on the fresh air side, and weld on a bung(s). To this bung(s) you inject distilled water.

Water? Gasp!

Yes, water. Because the air post turbo can easily reach 250-400 degrees, the water will instantly evaporate into steam. The evaporation process absorbs a fair amount of heat, and you can lower your post-turbo air temps significantly. The steam also keeps the piston tops crystal clean (assuming its distilled water). Of course one has to be careful, as if you're idling, you don't want the water jet to start slinging water into the engine... just under higher amounts of boost.

If injecting water makes one paranoid, you can make a 50/50 mix of distilled water and isopropol. Alcohol also will flash to steam at the upper range of those temperature, and even if it doesn't, it burns so no harm done. The droplet particles will be comparable to gasoline droplets from the injectors anyway.

You can even inject "zep" cleaning products if you like. I tried it on a single turbo 305 experimental motor, and it worked fairly well much to my suprise. And no, the exhaust didn't smell like oranges. It was rather disgusting, actually

Again, there are many, many variables to this and one can't really say what the best option is, because the answer always is "it depends"