33IMP
Well-Known Member
The law of diminishing returns.
Compression
- Thread starter F21
- Start date
-
I know first hand going from 7.5 to 10.2 makes a huge difference. I drive it around all the time. lol
thesiren74
Well-Known Member
I remember a magazine article years ago where they did a compression comparison on a 440 using super thick gaskets but can't remember the exact ratio they compared but I think it was around 60hp from lowest to highest.
Talking about CR I wondering your thoughts on this, a point I made in post #31, that keeps come back to me when I see conversations about cams cr and low end torque and it's hard to find a lot of dyno evidence in the 1500-2500 rpm range, but something doesn't add up to me.
I'm not really seeing the lack of torque in what dyno evidence I can find.
Like obviously bigger cams give up low end torque and lower cr gives up torque everywhere, but engines only seem like they can only go so low in torque (per cid) even at lower rpms like 1500-2500 rpms.
Guess question is there a minimal and or a non functional torque level around 1500-2500 rpm? guess it would be higher rpms for real big race cams. It just seem like were talking more about a cam with overlap not like operating at X rpm not necessarily the torque amount.
Eg. Cause even a 440 with very weak low end cause of big cam and low cr probably gonna have more torque than a /6 still. A stock /6 don't need a lot of gear and stall to function normallyand a big cammed 440 even with enough cr still gonna require a stall.
On the low end torque production, what you’re seeing in the videos and articles is the inability of the dyno to properly load and give an accurate reading. That is also coupled with the know perameters of the engine, which is more than likely a camshaft and etc…. That doesn’t make good power or at least not the point of focus under a certain rpm.
A good example of this is you have a cam that is 260@050, what’s the concern of how much torque you’re making at 1500?
If you’re concerned, there’s a problem and it’s not the engine or dyno.
If your cam is 200, 208, 218@050, the dyno will read it. The more radical the cam, the more the dyno has a problem loading at a low rpm.
Cam and compression are one think that is linked together in the package. Cylinder head flow is t really part of it in the basic question asked by the OP. But as 99% of the threads here, topic drift.
What does cylinder head flow have to do with compression outside of chamber size, IDK. You just keep on chasing that rabbit down its hole. Why? IDK. Not that it doesn’t lead to interesting thoughts and discussions…..
IDK (Again) if the OP is finding this curve Beneficial or not.
I hope he is.
Yup
Why do you think the dyno can't load properly and measure accurately at low rpm?
Newbomb Turk
Well-Known Member
The biggest source for those numbers is DV. And if you read all of what he said, he says that is the MINIMUM you can expect by a certain increase in compression ratio.
Making a blanket statement like Bewy did is not what DV said at all.
Newbomb Turk
Well-Known Member
You can load them down pretty low. You just have to have a reason to do it.
If you look at the video on post #54 there about 50 hp difference at peak hp, 700 vs 650 hp about 7% for 1.5 cr difference, there is a slight difference between the two engines, forget what they are.
At lower rpms the gap does get somewhat smaller hp wise might keep a similar percentage.
At lower rpms the gap does get somewhat smaller hp wise might keep a similar percentage.
Phreakish
Well-Known Member
Every dyno show I see where they start at 3 or 5k because 'lower doesn't matter' seems to stem from a lack of desire to tune down there. They just throw more converter at it as it's dripping fuel from the pipes.
OK. IDK a whole lot about these machines. A lot of times and even in here once in a blue moon, someone asks the question, and I don’t see much of a reason to be concerned with power output at 1,00-1,500 when your cam is something like 250/260+@050. No one is putting a cam like that in there car with 2/76 gears riding on 28” tires looking for street manors in the city. Unless you’re crazy? Maybe driving your top end machine built for something like a 1/2 mile oval track? But why would anyone want to build that for driving in rush hour in the city?
Yea, I know it happens….
Loading the dyno that low to know how much power it has at 1,000-1,500 with large street cams, small or big race cams seems silly to me.
Is there a reason?
Have you done this?
Why? For what purpose is that t needed to be loaded and tested @ such a low rpm with cams of 250@050 and greater?
What customer needs to know this and for what?
As I said, I only have been told what I said. I’m not arguing with them or you over it. I’d just like to know.
Have you loaded the dyno @ WOT with a 250*@050 cam down to 1,000 rpm?
I’ve been told it’s also related to the cam size and function of the build. If I have an engine with a sizable cam where any meaningful power comes in at 3500/4500, what’s the point of knowing what’s at 1K/1500/2000 rpm.
I’ll just live with what it makes and use the right converter coupled with the gearing and tire size to out out along. After all, the engine means business not at the low rpm’s but where it picks up.
This is what I noted on the shows and what I’d be after.
Phreakish
Well-Known Member
Definitely part of the calculus.
I can't speak for the dyno shows but it could be a matter of what they think the veiwers want to see and having to choose what to put in and what to leave out.
Generally on a dyno your gonna be concerned what a engine does during a full throttle run stall/corner to shift points.
Cruising around idle-2500 rpm your engine is generally only making enough hp to maintain those speeds which ain't very much. And the slight extra to go between those speeds.
Cruising around idle-2500 rpm your engine is generally only making enough hp to maintain those speeds which ain't very much. And the slight extra to go between those speeds.
B3422w5
Well-Known Member
I think a lot of people thinks it will tell them how streetable the cam is.
It’s amazing how many guys don’t get this even on a street strip car with cams as small as a 230/240@050
Phreakish
Well-Known Member
The power production may not matter, but if it gets driven anywhere below that range it can be nice to know how close the tuneup is.
B3422w5
Well-Known Member
Then I dare to say that the cam isn’t very large to begin with.
Dyno testing is about maximum and maximizing power where it’s making the power. If you or anyone wants to dyno there grocery getter, well OK then, have at it.
But to say, “it can be nice to know how close the tuneup is” is one very crazy thing I never heard of before. To me that’s literally insane. If you can smell it a rich runner, then pull a plug, read it, adjust the carb etc… for around town driving.
The dyno tune is only good for the dyno and taking it directly to the track expecting it’s a good tune is again, crazy.
If someone needs a stressed cam because there driving a street car for church and groceries, I doubt there’s a lot of guys driving around in a true daily driver everyday with cams at or greater than 230@050.
For that actual daily driver and drive anywhere at anytime with respectable mileage and street majors operating a slew of vacuum stuff, best cams are under 224@050. They make for nice easy drivers from idle to just off idle and will make good to really good power depending on the rest of the equipment being used.
Then again, some like that big waffen camshaft better than 250@050 in rush hour bumper to bumper traffic because the “Have the perfect combo of converter and gear and etc…..”
Ya know, the gotta be the big dog bad boy of the world….
Or internet and make the claims!!!!!!
For that actual daily driver and drive anywhere at anytime with respectable mileage and street majors operating a slew of vacuum stuff, best cams are under 224@050. They make for nice easy drivers from idle to just off idle and will make good to really good power depending on the rest of the equipment being used.
Then again, some like that big waffen camshaft better than 250@050 in rush hour bumper to bumper traffic because the “Have the perfect combo of converter and gear and etc…..”
Ya know, the gotta be the big dog bad boy of the world….
Or internet and make the claims!!!!!!
I always say, what ever you’re willing to live with……
Opinions vary……
If that person wants to daily drive there 12.5-1 - E85 swill drinking 275@050 single plane dominator feeding 5.13 geared bologna tired 33 X 15 , GOD bless them… I’m good…. There happy in there grocery getter/church going/school kid/soocer Mom/Dad machine in that configuration, heck, yea man, join them and GO MAN GO! God bless ya. IDGAF… you (anyone reading) call that a streeter? I don’t care… have at it.
I’m sure there’s some (internet) hero coming along any post now with a bigger and badder build I jokingly listed above that will be mad at me for disrespecting him directly even though I have no idea about him and his build. He’ll tear me a new asshole, defame me, **** on my head and make the big boast on how rucked up his car is… oh wait…. You ment to say how awesome his 3,400 HP/NA car is picking up the kids from school on a rainy day in slicks without driving issues because he makes tons of low end drivable torque.
-
