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| bottom end advice https://slantsix.org/forum/viewtopic.php?t=48468 |
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| Author: | Gclyne [ Mon Apr 09, 2012 7:09 pm ] |
| Post subject: | bottom end advice |
I am building my bottom end, its a 72 plymouth 225 slanter and am gonna put 198 rods try to spare and work with the crank but i need new piston and am going to upgrade the cam and valvetrain. Any suggestion on piston choice, cam, and valvetrain would be apprecitaied! Its going to be a performance daily driver! thanks and help or advice would be appreciated! |
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| Author: | slantfin [ Mon Apr 09, 2012 7:41 pm ] |
| Post subject: | |
There is a lot of useful info here: http://www.slantsix.org/forum/viewtopic.php?t=23314 . It's the Rosetta stone of everyone's engine builds. |
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| Author: | ceej [ Tue Apr 10, 2012 8:05 pm ] |
| Post subject: | |
Hmmm. OK, I've done a long rod build, though it was a stroker on top of everything else. There is some work to do if you aren't going with a stock stroke. This is where compression height comes in. I think Doc listed some pistons that can be used for this build. The problem with 198 rods is finding some. They pop up from time to time though. I have one spare set. They aren't for sale, just in case I need to rebuild the hooptie after something catastrophic. I run Toyota pistons from a four banger. There is a Toyota v6 that uses a taller compression height than the hooptie can tolerate of similar build. I'll have to look that one up again. With a more moderate stroker crank, they would clearance, though valve reliefs and mock up would be needed. They also run metric rings, which nets lower friction loss. Due to the long stroke, there can be flutter, which, with the relatively small bore and the lower oil ring wiping capability can result it oil smoke and plug fouling. This is generally at high engine speeds, so won't be a problem with a street driver. The Toyota pistons use a smaller pin, so the rods will have to be bushed. Gears: Anything taller than 3.55 gears is good out on the highway. 3.23's are pretty good all around gears for a driver. Shorter will tend toward uncomfortable engine speeds, and taller will not give the snap for town driving. The tradeoffs are obvious. Tall gears can deliver out on the freeway in terms of economy. Short gears can be more fun around town, and for short trips, driven sanely, short gears can help with city economy. If The K1 build ever gets cooking again, it is an excellent package. Based on the machine work required for using the metric pistons, the price is pretty attactive compared to a 198 rod. If the K1 had been available when I built my long rod stroker, I would have gone that way. Many of the top cars running at the strip today use K1 builds. Cam is another matter. Gears, converter, car weight, distances driven and so forth need to be taken into account, along with expectations. Performance and economy can be had, but high levels of either can be elusive, and become somewhat exclusive at a certain point. Much like an uncertainty principle, the better one gets at a certain point, the worse the other. When you start thinking about stall, the engine should run a few hundred rpm faster at cruise than the stall speed of the converter. If cruise is in the stall, the transmission will heat up. What specifically are your goals? 300 HP is not going to give you 20 mpg unless your going with a turbo build. A turbo build with long rods isn't going to be running pump gas in most cases. I get right at 20 mpg, driving at 55 mph. My E.T. coupled with car weight allows for around 275 HP at the crank. Depends on what flavor of calculator you use. A dyno would tell more. I have an idea the actual number is lower than that. The Slant makes great low end torque, right up until too much cam is applied. Top end is rarely useful on the street. I ran an Erson RV15M RDP deep into the 15's. Best of 15.03 Seconds. More cam killed 60', but got me into the 14's out on the high end. Your car is lighter than mine. A well thought out Stock rod, 9.5:1 build, with a moderate four barrel, better flowing exhaust, a bit better stall, the right gears, with Sure-Grip or some sort of locker, and perhaps a better ignition system will net you a lot. Brakes, undercarriage, and transmission will need to be addressed. Not sure if your budget will carry all that. When I decided to build power, my first stop was the brakes and suspension. I highly recommend you look into what you have, and what you can do to make it safer. Any car running into the 15's that is heavier than an early A-Body should have upgraded brakes and a sound suspension if it's running on the street. Check those things first. Build power later. Have you looked into what you have for brakes, rear axle, ratio and so forth? CJ |
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