V8 is 9.8:1

V10 is 9.2:1

Why do you think Ford made the V8 with a higher compression ratio (CR) as the V10?

How did they get a higher CR out of the V8 and do you think the V10 would benefit from the same?

 

Interesting, since higher compression motors are often higher performance. Maybe the V10 is lower comrpession in the interests of longevity? Or maybe it has something to do with the balance of vibrations of ten cylenders instead of the very familiar V8 configuration.

 

Ken

First, the diff between 9.8 and 9.2 is not very much in terms of power generation.

I have incrementaly increased the CR of racing motorcycle motors 0.3 to 0.5 in stages with dyno runs inbetween and you have to make large changes before much is gained

My stock 80-CI Motor was 8.2:1 and there was no measurable increase in any measurment until I got over 9.5:1 CR I was able to get all the way to 10.3:1 before pump regular 87 octane was pinging and ignition retard was not the answer

I suspect the slightly lower V10 ratio has more to do with mechanical leverage for the starting cycle then any performance (or lack of performance) concerns or engineering

Another thing to consider is that rated or listed compression ratios are all bogus any way and really mean nothing other then as a comparison or advertising gimmick (usually in high performance motors)

The ratios they cite are "static" ratios that are "calculated" based on CC of combustion chamber and bore and stroke volumes....

The real CR can be much higher or lower based on valve timing and is usually referred to as "Dynamic" Compression Ratio

Since Ford does not have any literature of specs that I can find on the Dynamic CR there is no way for us to make a relative comparison to the V8 static spec vs. the V10 static spec...could be they are really the same once valve dynamics are evaluated..

Seriously I have looked and I just can not find any reason for the discrepancy

I sort of lean to the idea the slightly lower static CR is offset by the two extra cylinders to arrive at the same mechanical leverage needed by the starter to flip the beast over.... that is purely a hunch and has zero basis or evidence for me to claim it as true

 

Not really sure why the V-10 has lower compression, but it would have NOTHING to do with engine balance.

V-10 engine balance has been discussed a few times, and there are differing opinions on it. I hope others read this and chime in. I have spoken with 3 different engine shops, all known for their high performance modular motors, and all have said that a lighter rod & piston combination DO NOT require anything special to be done with the counter balance shaft on the left side head. Some still do not belive this and I have spoken to one of the top engineers at SVT last week about this and he also said that the counter balance shaft does NOT need have anything done to it when going with lighter rods and pistons.

I know this is a little off topic here, but as you mentioned the vibrations in a V-10, I thought I'd throw this out there.

 

So many folks think that the V10 is simply a V8 with two more cylinders. Although true, in a sense, obviously Ford thinks a bit different. Something had to be done to lower it (or raise it in the V8). I was just curious if anyone knew what they did.

If the performance gain isn't that large for the .6 difference, then I kinda doubt the power required to start it would be also, right?

 

Ward's says that VCT and 3V allowed Ford to increase the CR and still run on 87 octane gas. They didn't say how the CR was raised... maybe they just shaved the head?

 

or they may have used a thinner head gasket!

 

The REASON it's different is because of the variable cam timing on the V8 which the V10 doesn't have.

The WAY they did it? Dunno... I just checked, and even back in 99-2003, the 5.4 and the V10 pistons were different. Not sure about part #'s, but one of the Ford dealer-parts web sites shows different prices for them.

Not sure why.

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As to the balancing thing, I still don't buy it - the whole point of the balance shaft is to counteract the 72-degree even-firing engine built with a 90-degree block. Not all the pistons are moving in completely opposite directions so as to cancel each other out. The balance shaft covers that up - and not all that well, based on the bellhousing cover/engine-seperator-plate buzz I get

I wonder if the effect of changing piston weights isn't even noticable, but there is a long-term problem later on down the road? Not enough to stop from racing them, but enough to keep it from hitting 200K+ miles ...

Just like the guys who raced them removed the balance shaft... eh?

 

Well, were to go on this one then. I understand the theory on it, and when I do my upcoming V-10 build I'm not going to worry about it.

When I talked to an SVT tech last week he couldn't answer me and refered me to another guy. I'm not sure exactly who I talked to but he was someone higher up in the engineering department at Ford SVT and was very intregued by my questions. After several calls and going up the ladder at SVT the last guy I talked to did not have to do any thinking on it at all and told me straight away that there was NO changes required to that counter balance shaft. He went into all kinds of theory on the V-10 72* crank and firing order, and spoke with high degree of confidence. We spoke in depth (20-30 minutes)on what I was bulding this motor for, he was very informative. So who do I listen to? Everyone is entitled to their own opinion, but I'm going to put up the bucks to build one and time will tell.

 

Time will certainly tell

If I tilt my head a certain way, stare out the window a certain way, and think really really hard, I can maybe see that the inertia of all those pistons moving in different directions, even on a power stroke, will be the same even if the pistons are different weights than original. Which means the balance shaft doesn't have to change.

But seriously, if the balance shaft will not be effected by changing piston weights, what is it really doing? The rotating assembly is 0 balance. WE THINK.

The pistons themselves, we know are moving in directions and at speeds that don't totally cancel each other out. Which is why we have the balance shaft.

I think the key might be that "don't worry about it". It's not as much of an issue as you think, and if you're pushing the engine to the limits anyway, you'll never notice a slight imbalance.

But, I'd be afraid of harmonics or something else - stretching head bolts, or some other effect to that head.

Otherwise, why did Ford even go through engineering that balance shaft? It has to be for something. And it can't just be the power stroke, because depending on where your foot is, that power stroke will be weaker or stronger, and the balance shaft is not changing in any way.

Whatever the balance shaft is for, it's a static imbalance. And everything I know about engineering screams at me that it's for the odd piston accelerations.

And if it's for that, then why wouldn't changing the piston weights effect that?

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Not arguing DD of D, just speaking out loud.

I certainly don't think I can argue with an SVT engineer, but ... you never know.

 

I appreciate all the comments, as I don't know everything either.
The counter balance shaft, as it was explained to me by the SVT engineer is to counter harmonics created when one cylinder fires and it does not have a running mate exactly 180* opposite. It comes back to that 72* thing, but is not affected by the weight of the piston/rod combo.

The head bolts won't be an issue, it'll get studs, heads, and mains.


And I can confirm the PSD intercooler is a direct bolt in. I just put mine in this afternoon. Took me all of about 20 minutes.

 

Lower compression is so you can add more boost..

 

Good point