Technical the pain of to much compression

Detonation is hard to live with. Quench is one of the best ways to fight it .060 or less I try for .040 distance between the top of the piston and the head surface. Unless the dish in the piston mirrors the the combustion chamber the dish killed the quench Add cubes inches the compression goes up I have repaired several 383s vortec that were built with a kit like this that were almost undriveable before you build do the math https://www.speedwaymotors.com/Street-SB-Chevy-383-Rotating-Assembly-Dish-Dome-5-7-In-Rod,36666.html?sku=91510242&msclkid=599be314d8391a23e1908327694b2ec5&utm_source=bing&utm_medium=cpc&utm_campaign=SMI - Shopping (CSE) (Bing)&utm_term=4577404348890847&utm_content=All Products (Feb28_2020)

 

I see no mention of the cylinder head chamber size , head material , deck height , chamber volume , head gasket thickness or camshaft used , all of which effect the compression ratio , even valve design effects both static & dynamic . What fuel was being used ? Nothing wrong with those parts , its what they're combined with !

 

If you have e85 available you can run 14 to 1 cr with no problems, I have a big block mopar that's 12.5 on e85.

 

For many years I believed the tale that I needed to have a compression ratio of least 10:1... Then one day I bought this Chevy el Camino with a 1977 454 with only 3000 miles on it.. Before driving it for the first time I thought it was going to be like a 6 cyl power wise. Wow, was I wrong, this engine hauls big time.. I think it has 8.5 :1 compression.. After a good tune up with some distributor work (HEI), I have the initial set at 22, the mechanical set for 36 all in by 2800 rpm, no vacuum advance, I also screwed the plate to the distributor to keep it stable. It came with Pypes 2-1/2 dual exhaust system with the X pipe. I removed the Pypes X pipe and mufflers and ran two separate 2-1/2" pipes into two 17749 Dynomax Turbo mufflers. Now it sounds like a big block.
It runs like a dream, if I mash the gas pedal at 35 it burns rubber LOL.. It's just such a nice running engine and all on 87 octane, it likes Sam's Club regular gas! I never would of dreamed of running such aggressive timing with 10 or 11:1 compression on todays 93-94 octane..
I also like how fast it starts, it seems like as soon as the key makes contact its running.

 

A 383 vortec would be a stroked 350 vortec dishes pistons and 64 cc heads figure flat pistons .010 down .040 gaskets and 4cc valve reliefs you get 10.9 Pretty shout for a iron head motor on the street. Cam can bleed off cylinder pressure but it does not change compression ratio.

 

Yes, a big cam/w a lot of duration and overlap will lower your DYNAMIC compression ratio. It is the dynamic compression ratio, not the static compression ratio that determines what kind of power an engine will make, the octane required to run it, and how it will run. Engines with aluminum cylinder heads can get by with running higher static compression, and it needs to. With all else being equal, an engine with iron heads will have a higher dynamic compression ratio. Your static compression ratio might give you bragging rights, but it's your dynamic compression ratio that's important. Two engines can have identical dynamic compression ratios, but their static compression ratios can be different. That 454/w 8.5 static compression might have the same dynamic compression ratio as an engine that has a higher static compression ratio.

 

Sorry , didn't see anything about vortex or iron heads

 

There it is. 7.0 DCR is safe for pump gas while some will run up to 8.0 DCR or higher if they know what they're doing.

This is where having a custom made cam really shines. Call the cam grinder, tell him your vehicle specs and goals and he'll give you just what you need.

 

I've had it explained that dynamic compression changes with RPM and is at it's highest at the torque peak of the engine, that is when cylinder filling is most efficient. So you can't ignore mechanical compression ratio.

 

Here's a Physics 101 lesson. When matter is static, it doesn't move. Matter is dynamic, when it's in motion. It doesn't matter what your compression ratio is when your engine isn't running. However, altering your static compression ratio also will alter your dynamic compression ratio. An engine with a bigger cam needs a higher static compression ratio because that same cam will lower the dynamic compression ratio. Both static and dynamic compression ratios should be calculated before building a performance engine. Most manufacturers will recommend a minimum static compression ratio, gear ratio, and sometimes torque converter stall speed. If compression ratio were not important, cam manufacturers wouldn't include it. They want you to be happy with your cam selection, but they don't want to hear you cry about it once it's installed.

 

I wonder how people get messed up on this in the first place when buying parts and building an engine. There are plenty of online calculators one can use just by punching in a few numbers to get you pretty close to your final c/r.

 

The aspirin for your 'too much compressin headache' can be summed up in two words.

SNOW PERFORMANCE.

www. SnowPerformance.net

Have your cake and eat it too!

Numerous folks I know run it or a variant of it on both carb and efi applicationd. Works great. Allows my kid's off topic twin turbo LS project to put 768hp to the wheels on pump 91 octane.

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Man, this place is fantastic, the shit I learn.......

 

768 wow that's a great number, I was tickled to get 455hp 445 tq NA from my 289!

 

Is this true??????? And I'm assuming static.

.bjb

 

yes it is

 

e85 makes slightly more power, engine runs cooler

 

If you have two engines built identical but one has .040 squish and the other .060 The tigher squish engine will be more detonation resistent .So dynamic compression is just one of several factors...
And there's the combustion chamber design.A faster combustion burn leves less time for detonation to occur..

 

I've got one that has issues with detonation due to high compression, and it doesn't need to be over 11:1 to have issues. Mine is a 350 4 bolt main with 59cc camel hump heads, and flat top pistons. It's 10.75:1 c.r. and it has issues at certain rpm's or if lugged a little when you roll into the throttle, even running today's crappy 93 octane and 10% ethanol. A little octane booster in the tank, or a little 110 race fuel fixes it right up. AND a big dose of race fuel makes it purr like it got it's favorite drink!
On my recent 350 engine build for my '39 Chev coupe I went the same exact route, except I used open chamber 76cc heads. The engine runs super strong, and even trying 89 octane on road trips, it still showed zero detonation. I've tried higher octane, and even tried some of my race fuel mixed in, but it really doesn't change how well it performs. It seems happy with 93 or 89 octane, and performs well on either.

 

I was going to mention Snow Performance as well. Water/meth injection is the shit. I run a stage 1 set up in my turbo Corvair and it has been a great addition. I never suffer from detonation. I have been running 100LL at gas. In my draw through turbo set up it acts as a intercooler of sorts. I have seen a significant drop in cylinder head temp as well. The tank and pump are mounted in the trunk. You cant even see the hose and nozzle and the seleniod is pretty well hidden. Great system worth checking out.

 

Beware of online compression calculators, which might not apply to every engine. I used gofastmath to calculate my dynamic compression ratio. It asks for Intake Valve Closing @ .050. Using that number, my dynamic compression ratio is 7.99:1. However, Ted Eaton (eatonbalancing.com) said that I could not use IVC @ .050 to calculate my Ford Y-block's dynamic compression ratio. Using my specs, he calculated that my actual dynamic compression ratio would be 7.56:1. gofastmath's calculator doesn't take into account valve lash of mechanical cams.

Regarding E-85, make sure your carburetor and fuel system is set up for it. Yes, you can run higher compression on E85, make more power, and run cooler. E85 also costs less, but you will lose MPG. Depending on where you live, you won't find a gas station that sells E85 on every corner. I know of only one in my town of approximately 60,000. Maybe they are more common in America's Heartland, where corn is grown.

 

I ran a 14:1 compression 460 Ford in my old Model A sedan in E-85. Runs very cool.. almost too cool. I ran a very small chopped 32’ 2 core radiator and had a hard time getting it up over 180 degrees. The tunnel ran on it would literally have frost on it sitting in traffic in the hot summer. You’ll need a completely alcohol rated fuel system, carb setup specifically for it, and a massive fuel tank. E85 only has around 2/3’s the energy as gasoline, so you’ll get 2/3’s the mileage or less if gasoline.. I got about 6 mpg with mine..


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I hear this a lot, but don't understand why. Why does the material the head is made of effect detonation? Not trying to argue the point, just trying to understand.

 

Water injection is traditional!

 

My understanding is that aluminum transfers the heat faster so less opportunity for a hot area to form. I think generally worth about 1 point on compression ratio.

 

Detonation is caused by multiple flame fronts going across the top of the piston, rather then one flame front starting at the plug. Often times the secondary (or more) flame fronts begin at a point where the compression may be higher (think the narrow part of a wedge shape combustion chamber) and is often started because of a high heat point in the cylinder. An iron head retains more heat then an aluminum head will because aluminum displaces the heat faster then the iron will. That is why the aluminum heads tend to reduce detonation. Gene

 

Use Sta-bil with E85. Even with Sta-bil, I would drain E85 from vehicle in long-term storage.

 

Aluminum is a better conductor than cast iron. Try this: Put an aluminum skillet and a cast-iron skillet in an oven. The aluminum skillet will cool very quickly once removed, but the cast-iron skillet will retain heat much longer.