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Old 01-01-2012, 03:02 PM
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Join Date: Apr 2011
Location: Florida USA
Posts: 1,870
Gender: Male
Vehicle: 1995 Dodge Ram B2500 Van
Trim Level: SLT - 2500
Color: Deep Molten Pearl Coat, Silver, Grey
Engine: 1994-2001 318ci (5.2L) Magnum V8 220hp
Rep Power: 4
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Originally Posted by Gen1dak View Post
So a turbo isn't practical. Well, let's look at that a minute. Take the 318. Figure 90% volumetric efficiency for the typical stocker. That equals approximately 286 cubic inches actual displacement in a naturally aspirated engine. Now, while up to around 9 psi IS SAFE FOR CAST ALUMINUM PISTONS (can you hear me now?), let's just figure on 7 psi. That's 1/2 atmosphere. So, with positive displacement under boost, you're looking at 150% displacement at 7 psi. In other words, at roughly 100% volumetric efficiency, a turbo 318 at 7 psi is displacing 476 cubic inches. Even if you weight that against less than ideal flow and the exhaust restiction imposed by the turbo, let's say you actually net 450 cubes under full boost. Are you seriously saying that going from natural aspiration of around 290 cubes to over 450 cubes isn't practical??? Even if the engine made 1/2hp per cubic inch that's an 80hp increase without touching anything else. In reality, it'd be closer to 3/4hp per cube on the typical stocker, meaning 120hp. Toss in a better cam and a couple tweaks and you have 1hp per cube. You've gone from 230 to 450. No way will your higher rpm + other mods approach come anywhere close. And how much higher could you go with that higher rpm scheme? Regular duty over 6,000 rpm's requires HD hardware (crank and rod bolts). Start pushing 7 grand and you need a forged "steel" crank and stronger rods. Now for the disclaimer. These numbers aren't cast in stone. Your mileage may vary, but the theory and reality are very close here, and it's basic physics at work. Your Dakota turbo fellow used too much boost or too much ignition timing, or both.
Regarding forged pistons. Umm, they're still aluminum, not iron. You think they'd cause too much drag? Tell that to EVERY 426 Gen II Hemi owner (and most other legendary engines ever built), EVERY race engine builder, every diesel ever made. They are designed to slightly greater tolerances so that when the FORGED ALUMINUM expands, it seals optimally. Confuse the PCM? There's this little thing called a timing chain. It keeps everything in correct time. The reciprocating system would need to be rebalanced for the heavier pistons, just like if a stroker kit were added, or you added all the guts I listed for high rpm's.
Finally, just because someone with more money than knowledge bolts something onto their engine and it blows up doesn't mean it won't work. It does mean they didn't know what they were doing.
I think you misunderstood what I meant by practical. By practical I meant that it isn't really common to slap a turbo on a dodge magnum. I didn't mean that it's a bad idea or anything like that. As for the 426 and diesel engines those engines are usually of higher compression and of well higher torque so steel would obviously be a choice among engine builders. You are correct about requiring a change of hardware when dealing with 6000 RPM, the stock cam and crank are only rated up to 4000 RPM. He might be able to use billet machined aluminum pistons. I personally don't like aluminum when it comes to things like the block and heads. I don't mind aluminum pistons. They can be made lighter and can operate under higher PSI, if made properly. Even if you adjust the timing chain to advance the timing the ECM will try to retard that advancement. The whole timing is controlled by the ECM and strictly the ECM, I have documentation from Chrysler for the Magnum engines and I wanted to get info on timing advance etc and well It said you can't adjust timing by chain or distributor. I figured so. Only thing messing with the timing chain will do on the magnum engines is pretty much nothing. You will be able to keep and exhaust or intake valve open longer but the ECM will pick up on that. The ECM in the Magnum is just like the ECM in the ford mustang engine from the early 90's it has to be tuned perfectly to function properly as far as timing is concerned. The magnum engine of course it's a precision engine it's not perfectly balanced but it still has it's stinkin requirements.

Turbo or not lets just wait until we hear back from the guy who wants to mod his truck.
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