Originally Posted by 14 apache

Good read.

Originally Posted by mike tkach

espically being wrote 10 years ago.

Originally Posted by mcollinstn

Did somebody say "automotive environment is more hostile than the performance marine environment"? Did somebody REALLY say that?

Did somebody say that the additional hours required of an automotive motor were one of the factors? Did somebody say that underhood temps of -30 degrees to 175 degrees were one of the factors?

Excuse me while I go drive my car to the market and back, never seeing over 2600 rpm, and never seeing more than 80 of its 320 available horsepower.

I guess I will touch on the temperature claims first...
If an automobile engine is started at -30 degrees, then it will obviously be in need of running a winter grade of oil, preferably a synthetic. It will be in need of a fuel control system that will take into account some pretty dense cold air, and adequately richen the mixture for such a cold stat in such dense air. Aside from that, and the proper antifreeze concentration and a good thermostat that doesn't leak, once she is spinning, it is a short time before the INSIDE of the motor is running in its familiar temperature envelope. Regardless of whether it is -30 or 175, the INSIDE of a car motor stabilizes at a specific range of temps. Maybe ten or fifteen minutes of cold weather warmup and it's all academic. Same thing goes on the high end. Closed cooling system temp is around 205 in modern computer motors. The OUTSIDE temp of the motor is not a significant factor.

Hours? I guess the average car with 100,000 miles has averaged 30 mph or so. That's 3,000 hours. 200,000 miles is like 6,000 hours.

But a car motor only has to put out around 45 horsepower to cruise at highway speeds on level ground.

The same 454 Chevy has been used in boats and cars for years. A pickup truck will usually have no problem getting 150k miles out of a 454.

A houseboat will go around 1500 hours of 2500 rpm cruising with a 454.

A performance boat that is run the way most are, will only give around 800 hours.

It's not hard to see why: The power requirements of a boat are a purely loaded curve. There is no "cruising" where you get to speed and the motor relaxes. This simply does not occur. For a given boat, X rpm = Y power. You can plot a graph, and then whenever you are spining the motor that rpm, you can rest assured tht it is being aked to put out that much power. Every time it is spinning that rate.

Performance boat application is HARD on a motor. It is asked to give a lot of its self in that duty.

Now to tunnel rams.
Straight is good. The less turns the intake charge has to make, the less fuel you "paint" onto the port or runner walls. In a "wet" intake (all carbs, plus TBI) any time you change the direction of the intake charge, the intertia of the fuel causes it to try to travel straight, thus taking out of suspension and slamming it against the outside wall of the intake. Textured surfaces encourage the air to pick the fuel back up, but you are going to have uneven distribution of the fuel in the air once it is slammed out and then pulled back into the stream. Best way to introduce fuel into the airstream is through an atomizer. A carb or injector does exactly that. It sprays tiny droplets into an accelerated stream of air, right into the middle of the stream. That's good. But once it slams out of suspension onto a port wall, it is now a puddle. Forced evaporation, and turbulence induced kinetic action is then required to pull it off the wall.

So straight is better. More fuel efficient for SURE, since you now don't have to overcompensate with extra fuel for the stuff you slam out of suspension and have to waste by adding more to get a decent amount in the final charge.

Port injected motors can make do with weird runner shapes because they have nothing in the air to get slammed out of suspension. The turns DO offer a more restrictive path than straight, but for packaging purposes you can give a little here and gain a lot there for dry intakes.

But there is STILL a good application for port FI with a tunnel ram. Gravity assists a small amount. Don't forget that air and fuel DO WEIGH something. They have mass. The gravity aspect is a minimal one, but it is still real nonetheless.

The long runners tend to focus the intake pulsing of a given cylinder more towards a particular venturi. You can tune for this and usually get an idle quality that is better than the shared plenum of a single plane intake.

You're gonna have some rpm ranges that benefit from the complimentary pulse tuning of the intake, and you are going to have some ranges that do NOT benefit from it. It is a matter of tuning and matching, just like anything else.

Carbs VS EFI?
You can tune EFI on the fly.
You can map EFI for a wide range of atmospheric/elevation deviations.
EFI will always be capable of better cold starts.

But if you run at a given elevation, and tune for a summer weather condition, then you can have great performance with known old school carb technology.

No need to argue about it.
mc

Originally Posted by SB

Reliability at extended higher rpm really hasn't changed, or gotten better enough. So...that's my guess why.

Originally Posted by bob

EFI driveability is super. Works super on the highway. When water/moisture come into the equation it becomes a different situation. You really need O2 sensors in the exhaust system and they don't mix with moisture. Played with a pair of the motors below for two years...went to blowers with carbs and life couldn't be better

Originally Posted by KAAMA

GLENNS just had Wesseldyk build him a pair of 565cid engines with hyraulic roller cams, 315cc AFR CNC ported heads, 9.3 comp ratio and 34* of timing. and tunnel rams that so far on WESCO's dyno have made 700hp on the nose @5400rpm.