I'm building a 500 inch stroker from a 440 block.
Block 10.700 at .040 over
stroke 4.150
rod 6.760
heads 84 cc

Heads are eddy Performer RPM with port and valve work. Cam will be a hyd roller

I'm looking for mid to lower 12's on pump gas

factory 883 4 speed, 3:55 gear, 15 inch tire

Car and driver 3800-4000 pounds

Car is mostly for street

How much compression do I really need? My engine builder wants to stay below 10:1 and I have no problem with that but will say 9.5:1 get me where I want to be? Is it better to sacrafice some compression for timing?? I'm in Tucson and it's hot and elevation is about 2500' I want about 600 pounds of torque from the engine.

Your thoughts

What kind of gas do you want to use?

just depends on the spec of the cam ,It will affect your compression. Also buy using an aluminum heads, you can knock 1-1.5 compression off the top , due to dissapation of heat from the heads.
I would go with 11 to 1 and pick the right cam .

I have personally built this very same engine, about 6 years ago. It ran strong, was able to push my 3800 lbs full interior 69 Coronet to 7.20's in the 8th mile, thats a easy high 11 second 1/4 mile pass.
I also ran pump 92-93 fuel also. Compression was right at 11:1
With a zero deck engine, your stroke and 84 cc heads your will also be 11:1+ my pistons were in the hole by .005-.008 with 4cc valve reliefs.
I set my timing at 32 deg total. This was plenty of timing for the engine, and help keep spark knock out of it also.
IMO having the compression up so high that it needs to be backed off a fair amount is a waste, and the little gain you tried to shoot for in the increased compression is now lost with the NONE optimal timing. You might even loose 2-3x as much pulling out timing. You would be surprised to know how much HP one can loose by pulling 8-10 deg out away from its optimal timing point. Maybe as much as 50HP in some combo's. Consider the gain you only get from 1 point in compression on a typical engine, what maybe 3%-5% overall.
So what on a 500hp engine you talking maybe 15HP??

fuel will be pump 91 octaine. I don't want to use more compression than I need. I don't know if 9.5:1 will get me there or not

I have just a tic under 11-1 compression in my 493 with flat Wiseco pistons and Indy EZ's.I run 93 pump gas with total timing set at 32 deg.and it puts my 3550# car at 11.13 @ 123 with a 1.8 60' time.
I just run a small street flat solid Comp XTQ series cam.
Gus

Dont get to hung up on base or static compression ratio. You have to really focus in on your cam grind .......that will give you your dynamic compression ratio, which will make or break your street combo.

I'll just say this; Listen to your engine builder. If your motor gernades, no one on this thread will loose anything but you. As the CR numbers go up, the HP gains deminish - rapidly. Leave some room for error. You ain't always gonna be pumping 93 octane, even if that's what the pump sez. What happens when you are running on the ragged edge of detonation and you get stuck in staging with the motor running and gotta leave hot - or you launch the fan belt at half track? Trust me, it ain't worth the additional 15 or so HP.

I am running 11-1 with 170 pounds of cylinder pressure in my 440 with indy heads. Tight quench, top of the pistons are thermocoated so are the cambers and the valves.34deg all in by 3200RPMs low first gear, 3.55 gear in the rear a 28 inch tall tire and 3900lbs. I seem to be on the edge with 91 octane mule piss that we have here.
Now this was with a tight converter, I have since installed an A-1 8inch converter and it seems to work great.
If your engine guy is recomending 9.5 compression it is time to find some one else. Give Bud yancer a call, he is not cheep but he knows his stuff and is easy to work with.

Mine is at 8.9:1 (493) and made right at 500 hp and 600ft/lbs. If those numbers will do the deed then 9.5:1 should put you over the top.

You are 1000 lbs lighter than I am and I'm running 13.90's at 101 with 2.76's and no traction (2.23 60ft)

Kevin

dont go 9.5 10.5 minimum.....the motor will more efficient also.

I've built and dyno tested a bunch of Mopar wedges motors over the years, stock stroke N/A pump gas street motors, NHRA legal "Stock" motors, high compression bracket motors and so on. 10.0 to 1 up to 10.5 to 1 comp. ratio is very safe with todays pump gas using the heads you have as long as you use a big enough cam to feed the motor not a RV cam The 4 speed and tires will determine how good the car ET, the motor will determine the MPH I built a iron headed (ported 906 heads) low deck pump gas 512 C.I.(4.25 stroke, 4.375 bore) stroker motor that had a true 9.25 to 1 comp. ratio. It had (I have since hopped that rascal up some more ) the ported big valve iron heads(same size valves as the stock Eddy RPM do), stock type six pak intake and carbs. comp Cams custom solid roller cam and kit. I had the motor dyno tested on a DTS engine dyno in Ontario, CA on CA pump gas, it made 644 ft. lbs at 4500 RPM and 612 HP at 5600 RPM I put the motor in my 1971 Duster, 3450 LBs with me in it with full 3 inch exhaust system and a full tank(stock 14 gal.tank) of pump gas, 727 and 315x60x15 ET Street radials, 727 trans, ten inch Continental converter, 4.10 gears in a 8 3/4 with ladder bars. the car ran 10:69 at 124.5 mph the first time at a 1/4 mile track. My car does not spin the tires at the track, it flat hooks and moves. I lived in Hesperai, CA 3300 ft. altitude, when I built that motor and car so the compression ratio was determined by the CA pump Gas and where I lived at that time The clutch and 4 speed trans will be the real channel to hooking your car up, sorry The motor will make all the power you need, maybe to much power Good luck

I plan to start building my 500 inch stroker real soon and it will be close to yours. I plan to use CNC ported Eddy RPM heads and I will run 11.0 to 11.2 comp at least and I still plan to use 92 or 93 pump. I plan on a pretty stout solid roller as I want to make alot of power out of it. I also plan to have nice quench in it as it will be a zero deck closed chamber head eng using a .039 head gasket. I want to have aleast 600 to 650 hp as I want to put my 3700 lb 63 solidly in the 10's. Thats why I will run at least 11.0 comp and then use a stout cam to keep the cyl pressure where I want it. Ron

If I was spending the $$$$ to go up to 500 cu. in. and aluminum heads. I think I would want all the CR I could get and be safe on pump gas. You can run 11-1 and be safe on pump gas. So why drop down to 9.5 CR and give up the extra HP you just spent all the extra $$$ to gain?

It is however wise to ask others who have run that just to be safe.

It depends on several things, including how much cam duration you will be running. I would build it with 10.5 to 11.0 CR and 260ish duration at 0.050". And that will be mild.

I ran 11.12 compression in one of my old combos with a puny 248/254 @ 50 solid roller and I raced on pump 93 and no signs of detonation whatsoever! quench on that was .052 (just sayin) good luck