Re: AMC 4-cylinder in a Spirit (Revisited)

[adh@xxxxxxxxxxxxxxxxx (Sandwich Maker)]

" From: farna@xxxxxxx
" 
" 
" Stock 4.0Ls are rated as peaking at 3200-3500 rpm, and one site lists
" 4000 rpm as the peak. I don't know what happened here -- I've never
" driven a 4.0L vehicle that felt like it peaked torque at that high an
" rpm. Sounds like a marketing ploy or a change in the way torque is
" rated. I thought for a few moments that it might be the CAM causing the
" higher fuel consumption over 2500 rpm, not the computer system -- but
" then my 91 and 93 Jeeps did the same thing with stock 4.0L cams. This
" leaves everyone in a bit of a quandry. 
" 
" Prior to 1990 the peak torque is right at the rated capacity, at least
" for carbureted engines. The last 4.2L made in 1990 for the Jeep
" Wrangler was still rated at 210 lb/ft @ 2000 rpm. The carbureted
" version of the 2.5L four is rated max torque at 2800 rpm, which makes
" sense. The MPI version max torque rating at 3250 rpm sounds about right
" for a four, I don't know where the max at 4000 rpm for the 4.0L comes
" from. Again, I think it's just marketing knowing consumers compare
" numbers, not types of engines, so they move the rating up in rpm to
" compare with V-6 engines. The rpm at such a comparatively low number
" like 2000 rpm doesn't look good when new model V-6 engines have their
" ratings so much higher. I'm thinking marketing just publishes a nice
" number at a comparable rpm, but then I'm just guessing. I'm totally
" stumped at why the high numbers when I know the engine pulls so well at
" much lower rpm!! 

i don't think they can actually -fake- numbers - but they sure can
-shade- them.

i recall reading that the [L88?] corvette 427 was officially rated for
marketing purposes as 435hp@5300rpm, and it actually made these
numbers - but the real peak was more like 535hp@6200rpm, and engineers
saw 600+ on a tuned-but-stock engine on a dyno.

i would expect a four to be cammed and generally set up more radically
than a six, just to better haul the same mass around with less power.
it'll have to pull taller gears, so tune it accordingly.

i don't think there's anything inherently different between fours and
sixes, unless it's long straight-six intake manifolds, and that
doesn't apply to the injected 2.5 and 4.0.
________________________________________________________________________
Andrew Hay                                  the genius nature
internet rambler                            is to see what all have seen

adh@xxxxxxxxxxxxxxxxx                       and think what none thought