A couple of points to add. A typical 318 has no where near 85-90% volumetric
efficiency. The fuel injected engines might hit that, but to hit the 100%
mark you would have to use turbocharging or supercharging, or do some very
intense porting work with fuel injection.
My second point is the numbers Mopar performance quotes on they're crate
engines is a dyno proven number, but it is also achieved using many other
non emissions parts(1 7/.8" headers, 750cfm holley, MP M1 manifold, etc.)
Third point is the crate engines that mopar sells are not low tech compared
to the magnum engines in the trucks. They use the same swirl port heads, the
same roller type cam as the magnum truck engines. They have just taken a
magnum engine and engineered it without emissions in mind.
I definitely agree with using an engine setup out of a magnum truck, even
the magnum 318's run better than the early 80's smogger motors. You would
need to use the entire computer and wiring to do it, but it would be a
pretty trick Imp when you were done.
Brian
----- Original Message -----
From: "D. Dardalis" <dardal@xxxxxxxxxxxxxxx>
To: <mailing-list@xxxxxxxxxxxxxxxx>
Sent: Saturday, June 08, 2002 9:23 AM
Subject: Re: IML: Hot Rodded 81-83s?
> At 08:41 PM 6/7/2002 -0700, you wrote:
>
> >I'm sorry, but NO these ratings aren't SAE GROSS
> >numbers. They're SAE NET,
>
> Chad, I am not sure about that particular engine. I guess its
> possible. One of the things I learnt though is that these after-market
> manufacturers very-very often have over-boosted claims. Is this one of
> these "typical" cases? I do not know. I can tell you one thing
> though. In order to get so much power out of a relatively small engine
> (without supercharging or benefits of a modern tuned manifold) there is
> only one way: Bigger cam to increase the operating power range, at the
> expense of driveability, durability, and fuel economy. Also, a rule of
> thumb estimating the necessary increase in operating rpm is the
> following. Say the stock carb high compression 360 has a net peak power
of
> 220 hp at 4000 rpm. Given that the stock engine has fairly descent
> head/manifold design with a volumetric efficiency of 85-90% at its peak
> power, there is little improvement you can achieve on its peak torque.
So,
> by maintaining peak torque and raising the rpm range (bigger cam, bigger
> valves, etc), in order to raise the power from 220 to 380, the peak power
> rpm would have to increase roughly to (380/220)*4,000= 6900 rpm. Such an
> engine would be useless below 3500-4000 rpm. For a 300 hp rating, the
peak
> power rpm would be 5450 rpm. Such an engine would be worthless below, say
> 2500-3000 rpm. Again, this is based on rough estimates.
> > Another option might be to check into an engine out of a wrecked 5.9L
> >(360)R/T Dakota. That engine is rated at 250 hp,
> OK, there you go. Consider this. This fuel injected engine with
> volumetric efficiency of probably over 100% due to its modern intake
> manifold produces 250 hp net. I am sure this engine has a relatively
small
> cam, but its peak torque is potentially higher than a carb engine due to
> manifold tuning. Are you sure that 380 hp of the low-tech crate
> engine? Its possible, but I am not sure how likely... By the way, I
> agree, this will be an excellent engine for an 81-83. If you get the
stock
> Dakota computer (I think you will have to) you will beat the 83
> emissions. You will still benefit out of the lower gears, say 3.23.
> D^2
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