Anyone running a Weiand 177? What kind of engine/compression/heads combos are you running? Also what kind of ignition system are you using, I was thinking about the MSD 6BTM.
It would be going on a 383, unsure of compression ratio, slightly dish pistons though. Not sure if cast or hypers either. Bottom end was built before I had the car. The heads I have on there are world products Sportsman 2's with 2.05/1.60's not sure if they are 64 or 72 cc combustion chambers. Cam is a 308/318 duration .488/510 lift 112 LSA
Would 5-8 lbs boost be too much for this set up? If so, would some aluminum AFR's be good? Also would be changing cam if changing heads.
Your thoughts?
Not, running one currently. Have run much larger ones though.
A 177 will need to be run aprox. 200% Over drive to make 10lbs. of boost on 383 with a 200cc. intake runner head and a blower specific cam.
Cast or hyperutetic pistons won't live long in a boosted application, especially if the engine ever detonates. A less expensive set of speed pro forged would be fine for 6-10 lbs. of boost.
You don't need to worry about dropping the top ring until you exceed 12-15lbs. of boost. The heat generated in the chamber at 15lbs. of boost will collapse the ring land on the top and second ring if the timing is not dead spot on.
A split dur. cam is a step in the right direction, because of the small blocks weak exhaust port. A 1.6 exhaust ratio rocker will improve power, slightly. Every blown engine I've ever built made more power with a larger exhaust valve compared to the intake. If a 2" exhaust valve would fit, it would be in there, even if the intake was a 1.94. You have to remember, the blower is forcing air/fuel into the chamber, but the piston has to push it out. The larger the exhaust valve and consequently the exhaust port, the less energy it takes to push the burnt gases out. Therefore, a large exhaust valve helps scavenge the cylinder and improves power.
All boosted engines will make more power with less compression and more boost, than more compression and less boost. Therefore, I would recommend no more than 8 or 8.5:1 compression and lower would be better. This almost always calls for a dished or inverted dome piston.
You don't need a forged crank or rods at street boost levels(6-8lbs.). Doing these things is just a waste of money. However, I feel that, increasing intake spring pressure by 30lbs. will keep the engine happy. How so?
Well, you say you have a 2.05 intake valve, which has a surface area of 2.56 inches and you are pushing 8 lbs. of boost on the back side of the valve which equates to 20.48lbs./ sq. in. of force( measured in boost) trying to open the valve when it is shut. Now consider you are running a valve spring with say 90lbs. of seat pressure, but you are loosing roughly 21lbs.of seat pressure due to boost. You should start to see why many builders will increase valve spring pressure.
What else? Perhaps, stronger pushrods. It is not uncommon to see bent push rods, in a boosted application. And, screw in studs.
The problem is most people just assume that bolting on a blower is a simple, bolt on. Many, do not realize that many other things need to be considered.
There is a book by SA design called, Street Supercharging. You can order it at Auto-zone. You should really pick it up. It covers most of the questions, you will have. And also points you in the right direction, for supercharging.
