Compression
I wonder if some of you guys mighta dropped the ball on this one.
How many 9.5 engines can you actually jump to 11.5
"with no other changes"?
I know OP didn't say, but if an SBM,
11.5 has the potential to quickly run the pressure up near to 200 psi;
Which I have run BTW, and it was fantastic!
Ima thinking 33IMP/ post #6, hit pretty close to home.
Ima thinking the 9.5 engine would have, had to have been, a less than exciting build to start with.
Love the post but the OP asked a general question and got a general answer. It’s all theoretical. All from a bunch of points of view.
@33IMP gave a sharp answer.
To address your question, “What engine can go from a 9-1 to a 11-1 ratio”, probably none in an afternoon. Unless you’re using the crazy thick MP head shim and two gaskets. But working with that, it’s an interesting thought on what happens.
Let’s take a typical zero deck piston in a 360 and use a .028 head gasket. Then use the old MP head shim designed to drop the high ratio engines for pump gas with 2, .050 Fel-Pro’s. One on each side of the .100 shim.That’s equal to a total of .200 extra space or just like dropping a piston down .200. That ought to do it?
Just enter in the cylinder head cc amount of 72, or whatever… & the diameter of the shim I can’t not remember but let’s make all of the diameters 4.185 just to keep it even and easy.
I didn’t run the numbers but it sounds like a 12.5 went to 7.8-1.
:rofl:
While a 9.0-1 ratio doesn’t create excitement with most of the performance enthusiasts, I well running and decent power maker it still can be. In my head, I’m thinking of something like a 5.9 Magnum.
I currently have an 11.3-1 - 360 and yea! Very nice and responsive. It’ll work with most any sizable cam. That ratio keeps the efficiency up very well. A 9.0-1, not so much with a sizable cam. This is where it’s all about & the problem incured with cam changes.
While in in general question has a lot of holes to wonder about, it leaves it open for an interesting discussion. One of the missing points is what cam is in the engine now, to how much larger will be out in on what compression ratio it is at now vs a change or 2 points higher.
We could have a thought process of one thinking the start engine is a smog 360, 5.9, zero deck 360, domed slug 360 for 12-1.
The move onto various cams from a very mild Comp 268H to a might rustyratrod “.750 roller!”
The effects of this would be tons of money on the dyno so please everyone, pray that I win lotto!!!!! I’ll be testing!
:thumbsup:
Yes, it was a hypothetical question me and a guy at work were discussing if the cam and heads could support it
I love these discussions at work. (When I was working)
No matter who was involved, car guys, racers or the fellas that only knew just a little bit.
That and the older guys or the fellas that knew the really old and semi old stuff with there pop quiz’s with hard or obscure questions. Fun times- fun times!!!
What you and your work fellas should understand is cam and compression ratio work hand in hand for best performance. I could take a whopping huge roller racing cam and install it in a low ratio smog engine (making sure everything clears of course) and run, drive, use the engine no problem outside of probable driving, idling issues. But the efficiency of the package is down in a really big way. The cam is huge and the dynamic compression ratio is garbage. The two have to be balanced as well as possible and there’s even wiggle room there.
On cylinder heads, the match is more of what the power output will produce. An excellent example of a sizable cam and a stock head is a FAST engine. Within the rules, there limited to a stock head and while there ported, they only port out so well for only so much flow. You could swap out the head and intake for a wild W9 or Victor head and pick up well over 100hp?
But the FAST package still runs some exciting numbers. The cam/cylinder head match was thinking is a myth I think people have created in a certain line of thinking. FAST engines defeat the myth in a way because there running really good.
Think of the cylinder head as not a component to match to stuff but an item to maximize breathing and cylinder head airflow for maximum performance. No matter what head you’re using, it will only release so much power due to its limitations of airflow. A good example of this can be seen on various episodes of engine masters. In one of the early episodes in season, one or two, they ported out a set of standard Edelbrock heads, and dyno the stock port versus the ported Edelbrock heads on a 408 Mopar stroker. It was a 92 hp gain if I remember correctly.
This shows the power release of a better flowing head. It’s not matching the head to the cam, it’s allowing the engine to breathe better. I have not seen a cylinder ahead on an engine, big enough to destroy power, however, it’s more of where the powers made, and how well it reacts in the vehicle, which is the real key, isn’t it?
I suppose if you took a ported W9 head and single plane intake and used it on a 7-1 318, there would be a lower loss. But this is an extreme and ridiculous route.
That’s why I said I haven’t seen a cylinder head on an engine to big and destroy or wreck power.
Freiburger attempted this with various cylinder heads and a small cam on a Ford small block, but as he stated - being the engine is a stroker @ 408…. Perhaps the CID should have been a 302 for that test?
