Other than the rpm difference, why would a V8 sound different than an I6? What if I downshift my I6 so that if the V8 were running 2100 rpm my I6 would be running 2800 rpm? Now we are both firing cylinders at the same rate and should sound about the same.

V8, 2100 rpm * 4 firings per revolution = 8400 firings per minute.

I6, 2800 rpm * 3 firings per revolution = 8400 firings per minute.

But then even that should not matter because each vehicle may have different rear end ratios. Therefore, there must be something else, some subtle variation in the sound. What is it?

 

The exhaust of two extra cylinders.

 

Im not sure what the actuall bore and stroke numbers are for the I6, but the I6 has a larger combustion chamber per cyclinder than a 302. You would think that the I6 would have a deeper sound. Kindof like the difference between a 1000cc inline 4 motorcycle engine and a 1000cc V-Twin motorcycle engine (the v-twin will have a deeper sound). There are other things that will affect the exhaust note though, like mufflers, headers, manifolds, and more importantly the camshaft geometery. I do know that most 302 motors produce an nice rumble with the right exhaust system, and have never personally heard an I6 300 with a free flowing exhaust. If anyone has some sound clips of their exhaust system, id like to hear them. As soon as i get my video camera im going to take some clips of my Bronco. It sounds pretty too

 

its all in the beat. Different firing order and different crankpin/puls angle. Most v8 have 90degree cranks and they sound great, but some (TVR and Ferrari and some drag motors) have 180 degree cranks that make them sound like 4 cylinders

cheers

-Griz

 

I have heard of the 180 degree (or single plane) crank for V8s. My understanding it's only advantage is to produces better exhaust flow by allowing a more balanced condition on each manifold.

Given the "beat" thing, I would suspect the v6 and I6 sound different, and perhaps a v6 would be easier to fake a v8 sound.

 

OK. Maybe this is nothing, but it dawned on me last night as I was lying there to go to sleep and contemplating the cycles of the four-stroke internal combustion engine. I thought (ignoring valve overlap and other technicalities), each each power stroke is 180 degrees of crank. So, a four cylinder engine is like a bicycle in that every 180 degree turn of the crank has one power stroke. Then as I thought about the six, and the overlapping power strokes, the exhaust sound thing popped into my head. The answer must be largely in how much the power strokes overlap--no overlap on a four, some on a six, much more on an eight, etc. as you keep adding cylinders. That and the balance/configuration of the engine (v or I or flat) must be the main factors in basic sound prior to the exhaust system/ muffler variations.

 

Hey Tall Paul,

I'm not a huge engine geru by any means but to me I kind of gotta disagree even though chances are you're more correct than me. See...to me if we're saying that on an I4 ever complete 360 degree turn is two power strokes (got that from you saying every 180 degree is a power stroke). Now from what I remember of small engine's class there we're actually 4 strokes, Power, Intake, Exhaust, and Combustion I think but don't really remember for sure so we'll just stick with calling them power strokes for now. So with what you're saying, every complete rotation of the crank on a I4 is 2 power strokes. And with the 6 cylinder, not sure if you were talking the I6 or V6 though, you said for every 180 degree turn, lets say its about 1.25 power stroke instead of just 1 because of the over lapping you say. So by this, for every 2 full 360 degree turn of the crank there is 5 power strokes. And you're saying with a V8 that it over laps ever more? This is the part that I disagree with because the way I see it is with a V8, each side is nothing but an I4. Granted, all 8 cylinders may be on a different timing and everything but I believe that each one is only going to power stroke 1 time for every 180 degree turn of the crank. Sorry if I'm totally wrong here but just sharing how I would view it. Have a good day.

James

 

As I understand it the four strokes (intake, compression, power, and exhaust) are completed in two complete revolutions of the crankshaft. A one cylinder then gets one power stroke for every two revolutions. A two cylinder gets one power stroke for every revolution. So you would divide the number of cylinders by two to know how many power strokes per revolution. Since each stroke is one half a revolution, a four cylinder would have a power stroke for each half revolution--or two per revolution. However probably the bulk of the work is done in the first 120 degrees of the 180 degree crank turn (near the bottom of the stroke there is nowhere to push the crank but sideways). Therefore in actual operation, a six cylinder probably dosen't have much overlap of power impulses with one power stroke starting every 120 degrees of crank turn (six cyl=3 power strokes per revolution, so 360 degrees/3=120), but an eight cylinder sure would with a power stroke starting every 90 degrees of crank turn (eight cyl=4 power strokes per revolution, so 360/4=90 degrees). Now look at the new Ford V10. It has a power stroke starting every 72 degrees (360/5). A v-12 every 60 degrees and a v16 every 45 degrees--pretty smooth, eh!

Not sure if I answered your question or just rambled a lot.

 

Hehe, definately took me back a good 7 years thats for sure. Yeah, you're right with the strokes, I remember that much. But I still don't know a whole lot about the degrees and all that stuff. I'm sure if I studied more on the engines then I'd understand more and would actually get more out of what you're saying. But I do understand to an exstent of what you're saying. Guess you could say thats why when I am ready to do my 2.3L (I4, EFI) I'll take it to a professional and have them do it for me. Hate to pay out that much money but rather not screw up my engine. As far as my engine goes, going to get a reworked head and ported, new cam kit, cylinders bored about .030 (or whatever the measurement is) over stock, new pistons, new reworked rods, a stroker crank that'll take it up to 2.85. Gotta save up and do it all at once though so it don't cost me too much and don't take apart and put back together over and over. Don't really like that idea at all.

Hey, now there is a question for you. With a different crank, is it still going to be two power strokes per revolution? Or would it change at all with the stroker crank compared to a stock crank? Just kind of curious since we got on the subject. Thanks for the info and setting me straight TallPaul. Have a great day.

James

 

A 2.85 liter four is (2.85x61) 174 cubic inch. You are going to have a nice Ranger motor there. I always felt Ford should have gone with a big four in the ranger. Now for a SuperDuty style hood and grille!

>Hey, now there is a question for you. With a different
>crank, is it still going to be two power strokes per
>revolution? Or would it change at all with the stroker
>crank compared to a stock crank? Just kind of curious since
>we got on the subject. Thanks for the info and setting
>me straight TallPaul. Have a great day.

No matter what the crank, all cylinders will fire in two revolutions and normally the firings will be evenly spaced (notable exception being the Harley Davidson V-twin). Now a two stroke engine is different (all cylinders fire in one revolution), but not normally found in passenger cars and light trucks.