What do u guys run for cranking compression

Mines at 160 would like to see it up around 200...whats your opinions..thanks rook

what's the motor set up???

It's a 60 over440 11.5 compression 67 heads fully ported big valves m1 intake cam is .645 lift intake .650 exhaust 280 at .50 intake 285 at.50 exhaust 106.5 Sep install at 103.5. .020 intake lash.016 exhaust

Was the engine blueprinted and the compression ratio calculated via measurement? That's a lot of overlap for hi cranking rpm pressures. Is there a particular reason you're looking for it?

what about advancing the cam or even a smaller cam. For more performance is the ign/carb dialed in.

I have 160 psi with this cam right now..i calculated the compression by turning the plug straight up..filling with fluid from a graduated burrett and it came out about 11.5 to 1 I'm looking for 200 but no one agrees on this number some say 150 is ok some say 200 is the best..im just wondering if I should change the cam or give it a shot..

There is no one "right" cranking pressure number.

What type of fuel do you use?

Cranking compression doesn't mean jack nothing. Hit your starter with 24 volts and watch the cranking pressure go up. Means nothing.

Complete waste of my time, as always.

This.

If you are using pump gas, you're pretty close now. You won't make 200 w/o using better fuel.

That's a ton of duration for a 11.5-1 452". That's why it's below expectations.
Doug

You have 280@050 duration? I'm surprised it even runs with that much duration. My pump gas 470 makes 775 hp and has 264@050 duration so I think your cam is way too big.

Back in the day I ran a stock 440SP motor with the CC.650/290@.050 SFT cam at approx 9.8:1, CP was only around 150psi, not ideal yes but it ran real sweet, ticked over@900rpm but only made 490flyhp on the track, weight/mph, mainly cos of the poor intake/small 850DP carb, not good enough 906's (255cfm) and of course the horrible weight of the bottom end, (2000gms per hole), still managed 10.6's with it....was planning to go to 12.5:1 pistons but it never happened.

170-175 w/an Isky solid roller 276-281 @ .050 470 cubes and fwiw, a buddy went low 8's a while back w/150...........

What Brad said....There is not a magic number. Look for consistency. You would be surprised what we are at for a cranking compression at over 16-1. TO many factors for their to be a perfect answer.

280@.050, 11.5cr, and you're getting 160psi?

Sounds about right........ Maybe even a bit more than I would have expected.

My 383 @ just under 11:1, 256@.050 solid cam in at 102 would pump about 200 in 8 pumps, all plugs out, wot, battery charger on, engine warm.

My old 448 @ 9.8cr, 259@.050 roller cam in at 106, would pump about 155-160 in 8 pumps, all plugs out, etc.

I know several of the FAST guys have combos that pump 240-260.
Lots of compression and short duration cams.

Cranking compression has a lot a variables, cam grind the main one, but not the only one. Performance trends engine analyzer will calculate what your cranking compression will be, give you an advance curve, and estimate spark knock for various octane fuels. Like every computer program garbage in garbage out, take the time to input accurate numbers and it is accurate within 10% used it for years. http://performancetrends.com/Engine-Analyzer.htm

I run about 220 on my pump gas 410 stroker in my dakota, 11 to 1 221@.050 cam, pulls like mad anywhere between idle and 6000 RPM, a shorter duration cam can bump up the cranking compression as can a bunch of other things like ring seal, engine temp, sterter RPM, valve seat seal...

What sort of heads do you have, ignition timing, and do you run on pump-gas?

My small block runs from 195-200 cranking compression with 10.9 comp. and a 255/266 duration cam. I have never ran anything but 93 octane pump gas. It has aluminum heads.

You could use more static for sure with that cam I bet. J.Rob

Totally wrong IME. Plug your compression gauge in and start the engine. Tell me what it says. J.Rob

I agree ^^^^^^^^^^^^^^^^^^^. J.Rob

Do not understand how fuel quality effects a compression test. J.Rob

You could absolutely use more static. Your buddy too. J.Rob

Agree about 1000%. Any of my real good engines pump 240-260psi and 150-160 on the first crack of the needle. Most people don't really track or understand a proper compression test. J.Rob

This I wish more people would take note of.^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Starter RPM is the only misnomer with this post.

You must be on top of the tuneup but man I bet this engine is incredibly fun and crisp.

I shoot for a minimum of 175 if the customer is VERY average and I shoot for 195-200 if a customer is VERY aware. J.Rob

You're right in the sweet spot for pump gas and aluminum heads. You still have a decently wide tuning window. Good combo. J.Rob

I'm fine thankxxx and running 6.15's at 112 in my street car tells the story kinda like leakdown #'s. Doug Sikora set a national record w/more that 20%.............

The number can be misleading. I picked up 15 psi opening my valve lash only .004 in, and I picked up 20-25 changing my old, early style starter for a mini starter.

IMO I'm also surprised you have that much with that cam and CR.

In theory starter RPM should not change it but in real life it does. If you had absolute zero leakdown it should not matter but turning an engine over on the stand would be impossible by hand if it held 200 PSI at hand turning RPM. Even with zero gap rings and such you can still turn the engine a little bit wait a little bit and turn it some more. At least I have never found one with complete perfect sealing.

Strictly speaking, even converter/flywheel inertial mass affects CCP - the engine slows down as it approaches TDC.

It doesn't. But apparently you were too busy being an expert to read and understand my post. At some point, fuel and detonation can and will be a limiting factor.

He has iron heads, and IF he is using pump fuel, he probably won't get to 200 psi without having a detonation problems.

I've seen engines with 160 cranking pressure rattle themselves to death. I've personally run 225 and ran what I consider a normal tune up and ran it on pump gas.

Cranking pressure means very little, especially comparing it to other engines. Maybe the same engine with the same starter and maybe you'd get some useful info.

What's the application/purpose of the motor?

From your earlier post, change the cam for sure. But not sure your thread is for a real info gathering or just a hoax fun question.

??

this is in my drag car..a 2700 lb 68 charger..i use race gas...and this question is not a hoax...lol

Never thought it was a hoax . What is max rpm you'll turn it?

Guess I will say that depending on rpm, your cam could be too large, or too small.

Ok, got you.. For pump gas 175 would be about the max, but since you use race gas, well over 200 if your octane is high enough.


The BIIIG problem with your car is that your cam is WAAAY to big for your comp. People have been saying that All along but you didn't seem to be listening, hence my hoax statement.

Change your cam to around a 260-265 max on a 108 LSA max and you will get your higher cranking comp and performance. Id also install it around 102/104 ICL as well. Id personally wouldn't go any higher the the 260 @ .050 Do that and I think you will be happy. No hoax here either.

Ask Mikeys Mopar on here about his "too big" cam and only 11.7.1 comp. and his 9.50 et's.............

I think there are alot of things that factor in that havent even been touched here. Looking back through my bracket builds one of my best stock stroke iron headed simple 360-s dynoed over 450hp and had times that reflected it with a 165 cranking and still needed a little octane boost with pump premium.

A 450hp iron headed 360 that would pull hard as hell from 1800 to 6000 is no slouch build weather at 165 cranking or 200 cranking. With the parts used on that build I dont think the combo could of took more cranking.

Unless one is way out on the cam choice I dont put alot of thought in CC, just what works and makes power for that pile of parts being used.

I live at 4k feet, my builds would not be even close for a sea level build with the same expectations or if I lived at 6500 ft.

Yeah, but not really a apples to apples comparison. Bigger heads, roller cam, etc, vs old 67 ported heads flat tappet.
He also had troubles with his 60 ft. Wonder why?? That may be fixed by now, but remember he started with 1.44 60,s then got down to 1.355, last I saw. A 9.50 60 ft should be around a 1.31, don't know where hes at now, but these two cars shouldn't be compared on Just the comp alone.

I get it but sometimes things run WAY better than most think and mikey's in the high 1.2" and his poor 60's had nothing to do w/his motor combo..........

Back in the day, built a 440-6 with unported 906 heads, weiand intake, 11-1, shift @ 7100, 289°/289°@.050" cam, ran 10-teens @ 3500 lbs..

Point is that a motor's need for air can outweigh a percieved optimum cranking compression, or a percieved optimum dynamic compression figure.

Say it ain't so............

I won't have to, hang in there........

Why do you want that cranking compression reading?
Have you tested your motor cold and then again when hot?
If not do that now
Then add a little shot of oil into the worst cylinders and see if their readings goes up or not, if not, find out why
I use a leak down meter to test cylinder conditions on the ring seal and valve sealing
The time slips and spark plug readings tells me if the car is slowing down or not