I hate having over 9.5 on a street motor.

Then they say just put a bigger cam in it to bleed off compression and you end up with a pingy, lumpy mess that's hard on starters and runs like crap...

I have a stone stock 1978 454 in my 69 el Camino and love everything about it!! Starts right up when hot, runs on 87 and has lots of of low end grunt...

 

I run what many consider high compression.. my dad and uncles call it normal compression.
Chamber shape or chamber efficiency and other factors will allow you to easily run 10.0-11 plus compression on 91 octane fuel.
The way I have done it for 30 years.
I port the heads and keep velocity in mind and use a rough stone to produce rough texture in the intake runners to promote atomization. large valves that are shrouded are a negative.

All sharp edges on piston tops are blended smooth as are sharp edges on the combustion chamber ..like the sharp edge left after surfacing the heads.
Think of it like this. You have a cigarette in your mouth and go to light it and there is 1 small piece of tobacco sticking out ..when the flame hits that small piece it instantly lights off that small piece.

If you have a stick up or chunk of carbon in the combustion space the heat from compression will heat that piece up to the point it can light off the fuel mix before the spark plug fires.
That's the way the old guys told me.

I was also told a cam with 224@ .050 would like 11:1 compression..I built just that years ago and it ran excellent. and had 245psi cranking pressure.was a 350".
same short block that is in my below 57 4door chevy.


I just pulled my 268H from my 350 that has small chambers 57cc and 10.87 compression and stuck in the 280H. It is in a 3800lb race weight 1957 210 4 door.
I ran it for 6 plus years pulling trailers and racing, it liked 35 total and 38 total timing only made 3 more HP at the wheels. No it is not fast.. it is just fun and reliable.

Not finicky at all.. I keep coolant temps in check.
I just installed 3.00 gears and pulled my 20 foot pontoon to the lake with the 10.87 compression 280H cam 350.
My trans is a TH350 and converter slips a lot for a 2500 stall. Pulling it this week for a tighter converter.
Yesterday during pulling the boat 100 miles the coolant stayed at 190.
I feel that is a bit high but no issues.. timing is all in by 2000 rpm and 38 total.
190 is not really high but if I can keep it just under that I feel better. 190-195 is nice for MPG though. Atomizes fuel better.



Built a 396" for a friend and it has 11:1 compression 280H cam and 210 psi cranking pressure his vehicle is 4200 lb chevy truck.
He pulled trailers with tractor and brush hog on it for many years.
His likes 38 total timing.
Ported heads roughed up intake runners. 91 octane fuel.

Maybe the deal is my cams are not large and do not move the amount of air that a racing cam would.
maybe if it had 11:1 and a 700" lift cam the cylinders would get filled with even more air and then I would have issues with 91 octane.
That I have thought of many times.
All the above have iron heads.
Maybe the rod to stroke ratio has something to do with it.. but i doubt it . I ran 57 cc heads on a 385 stroker with .045" piston to head clearance with flat tops that had 5.5cc valve reliefs.
I ran the 280H cam with it and it ran fine on 91 octane. Ridiculous power everywhere.. hardest thing I have had to get traction with in a sbc .. stupid thing always wanted to spin the tires.

Now taking it much farther the 5.0 mustang was dropped for a few years then they brought it back.
Talking the engine the 5.0.
In 2011 compression jumped to 11:1..How do they make it happen..I asked a buddy at Ford to send me the specs.
I figured it was a long rod and very small chamber. and it was.
I see for 2018 they increased the compression to 12:1 in the mustang.
They must warranty these things.

It can be done. but using a bone stock runner and chamber with zero massaging I would think it should not be attempted.

 

My engine has a true 10.7:1 compression and runs on 93 octane without issue.
It made maximum HP at 35* of timing and I keep it around 33-34* and it does not ping. Not good for head gaskets at the HP level.

 

FWIW,my cam is 248/254@.050 110 LSA solid
Can't say I have checked the cylinder pressure with this set up.

BINGO!!!! That right there^ is a fairly big camshaft by street car standards, and is definitely the primary reason a person can run a fairly high static compression ratio on pump gas. The cam is one of, (if not THEEE ) biggest factors in dictating the requirement for the static comp ratio on a pump gas motor.

Not only CAN you run higher comp ratios with 93 octane gasoline in engines with long duration camshafts, but most cams, (not all) with longer durations actually NEED bigger static comp ratios to run good, and make good power. I ran an honest 11.0:1 comp ratio with 93 octane gas without retarding the ignition timing on a 355 cid chevy engine with a comp cam bumpstik having a 244 degree@.050 duration, and it ran great without even a hint of pinging, even when I lugged it up a hill in 4th gear.

I had previously run this same combo with 10.2:1 comp ratio, (using a thicker head gasket which ofcourse lowered the CR) and it had less power, and less throttle response. So that camshaft actually needed the 11.0:1 CR. But it had no problem with 93 octane pump gas at all. I wouldn't have been able to run that same static CR with a camshaft having 225 dur@.050 it would've pinged itself to death.

The main consideration is how long the intake valves are held open, (which obviously is dictated by the camshaft choice). That comp cams bumpstik I had installed in that SBC engine, didn't fully close the intake valve until the piston was 1/3rd the way up it's bore on the beginning of the compression stroke. Therefore, the entire bottom third portion of the compression stroke was lost as far as compression and cylinder pressure is concerned. So with a performance cam like that, you NEED to run a high static comp ratio, or the engine will run like a tired dog.

 

My 70 had a 12:1 454 when I purchased it. It had a monster cam, no vacuum, barely idled, and sort of ran OK with the highest octane pump gas I could find. A couple of times it kicked and ran backwards, very freeky. Eventually it ate the cam because of the valve spring pressure. I took it apart and washed out, milled the pistons down to get to 11:1, put in a smaller roller cam and softer valve springs and now its a much more behaved street car. Still needs the best quality pump gas (Shell premium only) and every so often I treat it to some racing fuel which it really likes!

 

Running near 10:1 with iron heads and runs fine on 88 octane ethanol free gas. I do live at 6000’, and have a large enough cam that bleeds off enough cylinder pressure.

 

My Mach 1 has 4v351C with 11:1. It requires octane boost with premium fuel. I only drive about 1 to 2 tanks a year through it.

 

We'll get into this whole dynamic compression discussion, as you cannot compare mechanical compression without discussing the cam events. So while mr 4 speed can run 10.75 with iron, I have issue with 10.2 with iron. 215 cranking PSI is too much for the street it would seem. I had little issue at 10.75:1, 195 psi and alloy heads ( different cam) .

 

FWIW,my cam is 248/254@.050 110 LSA solid
Can't say I have checked the cylinder pressure with this set up.

 

Flat top pistons and small cc heads with thin gaskets. It's been years, but it worked for me many years ago. Oh, I had a small circle car roller camshaft at that time, so not a lot of overlap. I loved the 7500 rpm capabilities it gave. Triple valve springs and all.

 

every time this subject comes up all these guys start weighing in with how they're running all these high compression ratios with no problems. I don't see that myself. with iron heads and a reasonable street cam I stick to about 9:1 or a little more. At 10:1 real CR it'll be pinging. You might get by with retarded timing. or not. it'll be sensitive to a tank of bad gas.

Flattops in a BB are a pain because the CR will be too low. A flattop 454 with open chamber heads might come in with under 8:1. even a 496 with flattops and OC heads is very low. You need to settle on what heads you want to run first. A flattop 454 with CC heads can be a pretty good running deal.

Threads like this always remind me of of threads about how big is too big on carbs. first thing you know every is running a Dominator on their 283 truck engines. .

 

if I actually build a motor, new pistons etc. I would run new 110 cc rpm heads since they are already new in the box, sitting in the shed.
if I go used short block, with new rings and bearings I would use a set of 063 closed chamber heads sitting in the shed. jim

 

396 + .060, L2242 Speed Pro pistons (38 cc dome), stock-decked 5272 4-bolt block, lightly surfaced 840 rectangular port 107 cc heads, .038 head gaskets, Howards solid FT cam w/Comp Cams 1.72 rockers yields .545 valve lift 242* duration @ .050 on 114* lobe centers, stock GM 163 intake w/780 Holley, headers, MSD Pro Billet distributor w/12* initial timing and 37* total at 2,700 rpm, M22 w/3.73 gears. Approx 11:1 CR, excellent power/throttle response and I cannot make it ping on 92/93 octane Chevron/Union 76 or Shell pump gas.

 

Another idea thrown at me was to just take the block in, have it cleaned, bored and cam bearings installed and order a balanced flat top 496 rotating assembly and drop that in and go. Is it really that simple? jim

Do this. You'll have plenty of power and be able to run today's crappy fuels with no issues and no octane boosters.

 

Amazing, Tom and Gene. I wonder if we have better gasoline in the NW or what? We sure pay a hell of a lot for it @ $3.79/gal...and sometimes more. I am near sea level out here too.

 

Having a computer, injection and knock sensors help.
The engine in my daily is a 355 with 4VR flat tops, no dish. This is a '97 Vortec engine. Block was zero decked. CR calculates to 10.1:1. LT4 cam, so just a bit hotter than stock. I run cheap pump piss, have never bought anything other than regular. Never had any issues, period.

 

496 with 10.8:1 compression AFR 265 Heads, Vic Jr intake 1050 holley , 254/264 @.050 (112) hydraulic roller cam. Absolutely no problem running 92 octane.

My other engine is a 555 with AFR 325's, Holley strip dominator, 1050 holley 11:1 compression 264/271 @ .050 (108) hydraulic roller. Also no problem with 92 octane.

 

So many variables involved besides static compression. I ran 10.9:1 compression for years when my car was a daily driver. It cranked 215-230psi cold and ran fine on 91 octane. I later built a 13:1 357 when my car was not a daily driver. I didn't care if I had to run race gas. I did a cold compression test on it and it made 195-205psi. I ran 91 in that engine also when driving on the street. I ran nitrous so I would run race gas when at the track. The cylinder pressure was lower on the 13:1 engine because of the difference in camshafts.

I think I was able to run higher compression on pump gas because the car was relatively light at 3,150 without me, plus aluminum heads, 4.10 gears, loose converter (4,500) and reasonable cylinder pressure because of the camshaft. If either one of these engines was in a heavier car with taller gears and a standard transmission, I don't think it would handle pump gas very well at all.

 

Yeah, I donnow. I do know my cam is advanced., I almost want to pull the balancer ,cover and degree the cam to more straight up. I know it'll knock down cyl pressures. Also, I;m **only ** at 240@.050 and want to go to a smaller cam, not 255 or 270!

PS, the vacuum advance has nothing to do with most WOT pinging issues, mine clearly does not, although it is limited. Yet,not relevant at WOT. And some of us put highway miles on the car, so its nice to have on.

 

I'm running 11:1 on my 406sbc with AFR227 76CC alum heads with 280 Comp cam HFT.
The timing is 100% mechanical advance.(never did like vacuum advance). Level off 36* @ 3000RPM. I use Sunoco 93 octane and It runs fine, No issues with pinging. I have 215 psi cranking.

 

Too much insanity here to comment on.

Set the quench right, .039 to .045.

Use a vacuum advance degrees stop - the right way (on the diaphragm side of the pull pin, NOT OFF THE REAR SCREW), 8 to 10 crankshaft degrees only, then use full manifold vacuum, and it'll work well. 12/13 initial, add 8 to 10 with the vacuum canister, 22 mechanical curve. Done right, initial, 12/14, idle, 22/24 (full manifold vacuum), total (initial and mechanical) 34/36.

 

We finally agree on something, 8-10 degrees with vacuum advance, 34-36 total.

 

On full manifold vacuum sourcing, NOT PORTED. This will require a stop for the vacuum advance pull pin, AFFIXED CORRECTLY TO THE VACUUM ADVANCE MOUNTING BAR. Complete FREE package on how to do it right is available, ask for one.

 

I fully understand why you want vacuum advance on full manifold vacuum for street driving, completely understand. For street driving it's absolutely a great way to do it. You have less initial advance which greatly reduces the chance of kick back. The exception I will interject and the reason I run more initial timing and less mechanical advance is my cars have always been street/strip cars. 90%+ of the motors I've ran need the 22-24* at idle to make the engine idle properly. Makes no sense to me to have the timing drop back from 22-24* to 10-12* when I stab the throttle and experience a hesitation from the reduction in timing as would occur with vacuum advance on full manifold vacuum. As long as my motor turns over with no signs of kick back, to me it makes absolutely no difference, I'm still getting the same total timing and vacuum assisted timing at cruise.

 

I work in the oil field and I can honestly tell you that gas octane is different by region, they have winter blends and summer blends despite the octane ratings. Being that you are in Arizona and its always f n hot there you will get a better gas blend. So you can probably get away with a higher compression, probably even more if they sneak e85 in there cause it will run a bit cooler.

 

I've often wondered about Rame's point, regional differences in fuel. BTW, I think part of my issue is that I run the tripower on the lean side. It'd ping less if I fattened everything up. In fact, a recent track time tells me power is off, so it maybe time to go thru the carbs. I hate the fact that you cant read plugs so much anymore.

 

Those that insist on not understanding vacuum advance, AKA "load compensator", are doomed to "live with the ping".

Gene, that ain't aimed at you, richen the trip's up.

 

That sounds like a blanket statement to me. However I'm not really sure that you meant it to be. So for clarification, I'd like to pose this question: Are you meaning to imply that such combinations as 13.5:1 static CR or even 15.5:1 CR can be run on 93 octane gasoline alone without pinging if the "correct" vacuum advance formula is used? Are you actually implying that any camshaft, and valve timing, and any static CR combinations can be run on the street with 93 octane pump gas as long as the vehicle in question is set up to take full advantage of vacuum advance?

 

Dave, I'm using the adjustable can you provided. Its the dang 215 psi, iron heads, lean mix, and 3.31s gearset on a land barge that's not helping! Plus, I think a TQ converter helps this along as well, as opposed to a clutch. As Steve said, its a system of simultaneous equations. I will say that I tire of always puckering on fuel and plan a true 89 octane mill next time to have a bit more drama free experience.

P.S. The cam guru warned me to not go much above 10:1 , esp with iron heads as the cam has a huge "ram" or filling effect. 9.5 tops with iron. The 427 sits at 10.15:1 with the 781s on. Yup. Right again. Wasnt an issue with the 074s with 4cc smaller chambers giving near 10.5. ( 112.5 v 116.5cc) Other option is some 120CC bathtub-sized 049s.

From his grave, Harold speaks wisdom and truth.