Originally Posted by MAG58 (Post 2537944)

Hmm....
V8's are still not light engines.

KA24DE = 368lbs (Source: Drifting.com)
Ford 5.0L Weight = just under 460lbs (source: gomog.com)

I'm not sure where you got that a 302 ford is anywhere near the weight of an I4.

V8's require a substantial amount of work to be a 'revvy' engine because by the nature of the design, they require heavy first and last counterweights. Unless it's a flat plane motor. Then they're very displacement limited and still vibrate. I've built both, and if they're both setup right, the I6 will still out turn a V8 unless it's a small displacement motor vs. a larger displacement under square I6. Again, perfect balance means a bunch of weight can be taken out of I6 bob weights. Unless you do like BMW and put heavy metals in the counterweights ($$$) you're dealing with big, ungangly counter weights lest you like vibrations.

And what are your statistics for highway mileage here? The LSx is the only engine that comes to mind that is close to the modern I6's in mileage relative to body weight. The Atlas I6 did very well against the 5.3 LSx despite having over a liter of displacement disadvantage. I'm not sure what ratio you're talking about here, but there are also surprisingly few V8's that have decent rod/stroke ratios and even fewer that have bore/stroke ratios near/above 1:1 any more. They keep trying to be more compact which means bore goes away in leiu of additional stroke, though unfortunately rod/stroke ratio suffers.


Yes, Iron I6's are heavy because they require a substantial amount of bracing within the engine to dampen NVH of a crank that long. But the aluminum I6's are not heavy at all. Have you weighed the current BMW N series Aluminum/Magnesium I6's? They compare VERY well to any OHC V8 save maybe the featherweight UZ engines.

Packaging is a relative issue. I can tell you right now that an I6 is much more friendly to work on in the long, narrow hood of my 240Z whilst a V8 accommodates much better to the short, wide engine bays of the current trends.

Originally Posted by MAG58 (Post 2538133)

I'm fully aware any configuration can reach a certain rpm. I was referring to 'revvy' as the ability to change rpm's rapidly and gain rpm's rapidly. If you were running the stock crank there was a ton of rotating mass there. Yes I've seen hemi's and built BBC's and BBF's, none of the cranks are light in the counter weights unless they've had a bunch of work done to them.

Originally Posted by 400Eric (Post 2538358)

And let's not forget how the 308ci Flathead straight six Hudson Hornets tore up bigger, overhead valve V8s on the NASCAR tracks in the 50s!

Seriously, it is really hard to do a proper A-B comparison between I6s and V8s because the I6s for some reason tend to have poorer rod length to stroke ratios and poorer bore to stroke ratios than the smaller V8s do. And yes, we do have to use smaller displacement V8s so we can have similar displacement engines in this comparison. For this comparison to be valid there can't be any other variables.

I'm no BMW guy but their little 3.0 V8 might work for such a comparison but the problem is we would still run into the problem of their sixes having poorer rod length to stroke ratios and poorer bore to stroke ratios than that little V8 does.

You guys are gonna hate this but I think one valid comparison is the Big Three's pick-up diesel engines. They are all similar sized, four valve turbo engines and they are all comparable in performance in both stock and modified form the only difference being that one of them is an inline 6 and the other 2 are V8s. Maybe it winds up being a moot point. (At least as far as trucks go anyway.)

I dunno, like I said a few pages back, I kike em both but Roncallo has me fantasizing about V12s too.

Hey Shoomakan, do you know board member Jay Rash? You guys should hang out!
Regards, Eric

Originally Posted by 400Eric (Post 2538706)

"Overhead valve will rev different then side valve.
Pushrod versus SOHC or DOHC
Chain driven, belt driven, gear driven cam..
Compression ratio...very important because it's what drives the crank."

Yes, All of these and more.....

For this comparison to be valid, both engines need to have the same head/combustion chamber design, the same induction/breathing/fuel delivery, the same bore to stroke ratio, the same rod length to stroke ratio, be the same displacement, be installed in the same chassis, preferably be from the same manufacturer. I don't think we can possibly meet all these criteria so I don't think this question will ever be properly answered.

In the meantime I'm working hard to spank that C36 on our next track day 9/18/10. Looking for a couple of tenths!

With all of this "I6 vs. V8" talk, this race is the only case of two guys actually putting it on the track to find out! Yes, it's less than ideal in that it's just straight line racing and doesn't meet hardly any of the above criteria but it's all we've got at this point unless some of the rest of you attempt to do better! Who's gonna come watch?
Regards, Eric

Originally Posted by MAG58 (Post 2537785)

I was thinking it was the 145mm rod too but if I calculated right, the CR on that is tiny. I checked EPC and while all other M104's either carry M104 or the M102 number (149 or 145), EPC listed the rod as an HWA part # (AMG Specific), though there are plenty of non HWA parts in the motor.

Just remember, BMW turns 8k on a 91mm stroke 139mm rod in a much more distended engine.... Hence my inquiry.