The 3.8 engine.

[lee-type]

Good evening guys


Im sure this question has been asked a lot of times but i am interested in your thoughts.

I am under the impression that the 3.8 engine like to rev more than the 4.2 but why is this as both engines have the same con rods and the same length stroke.?

Have you owned both engine sizes?

What is the 4.2 engine like with a aluminium flywheel?

Cheers

[christopher storey]

I have had both engines and have never really noticed the difference , although it is fair to say that I am not one for thrashing the guts out of an engine . However, the detail design differences undoubtedly can make a difference in theory

1. The pistons in the 4.2 are that much heavier

2. The flywheel in the 4.2 is about 40% heavier

3. There are the offset combustion chambers on the 4.2

What I can say from personal experience is that static and dynamic balancing of a 4.2 as it is built up makes a colossal difference both to its smoothness and its throttle response . It cost me from recollection about £150 in 2009 and was some of the best money I ever spent

[Heuer]

The 3.8 was a more free revving and sweeter engine than the 4.2 but with modern rebuild technology you would be hard pressed to spot the difference on the road. But yes the 3.8 is nicer to drive quickly, the 4.2 more effortless. Whilst lightening the flywheel on the 4.2 can improve throttle response it makes the car more tiring to drive especially in modern traffic conditions

Avoid the ali flywheel like the plague as it will screw up the entire driving experience unless you are on a track day. Even then I doubt an ali flywheel would make the car any quicker.

[abowie]

The essential difference between the two engines is that the 4.2 has noticeably more low down torque. This equates to the "effortless" feeling David refers to. You can drive a 4.2 in 3rd gear all day and no matter where you are in the rev range it will respond when you touch the throttle.

It's not that the 3.8 really revs better, but more that you need more revs to achieve the same effect.

I fitted a Fidanza aluminium flywheel to my first 4.2. I don't think it made the car quicker, but it certainly made the engine less smooth at idle and harder to get off smoothly at the lights. I would not do this again.

[Tony W]

If you have a reliable method to time acceleration in gear, youll find with the lightweight flywheel a measurable difference in the time it takes to accelerate the heavy flywheel up to a particular rpm vs the lightweight one.
The effect is more noticable in 1st gear due to the mechanical advantage of running in that gear and it gets less pronounced as you select longer gears (boo!).
What this results in is an engine that can climb up the rev range faster although it gives no extra power at all.
Read up on Newtons 1st law (object at rest stays at rest unless acted upon by a force) and a rather grandiose term "Radius of Gyration" which explains far more eloquently than I ever could. :)