10.2 : 1 compression 360 at sea level. Options?

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SBM4theW!n

SBM4theW!n

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Just moved from Denver to Austin Texas, and I'm looking for ideas on what to do with my 10.2:1 static compression 360.

In Denver the engine had no problem running on 89 octane due to the altitude, but I'm assuming I'll have issues here (sea level) running pump gas. I know I could just run race gas, but what octane would I need? What other options do I have? Last choice is adding a head gasket spacer and shooting for closer to 9.5.

Engine info -
Open chamber, milled iron heads. Ported and smoothed sharp edges.
No quench , .039 Felpro head gasket
360 30 over with hypereutectic pistons (SLP-H116CP30).
Comp Magnum 280H camshaft
Engine runs at 180 degrees, but climbs in hot weather while sitting and would probably be a time bomb running 93 octane.
Manual Trans, 3.23 gears.
 
Run 93. I ran a 360 @ 9.8-1 with J heads and the MoPar purple 292/.509.
Manual trans, 4.10's.

You can run a .054 Fle-Pro to cut a 1/2 point out in compression.

Possibly a better cooling system. I ran a fresh recored radiator, MP viscous 5 blade fan and OE shroud.

You may have to limit total timing a few degrees. Worst case tha is.
 
I thought about putting in a bigger camshaft, but I like the streetability of the comp magnum (I have power brakes).

In terms of cooling, I do have a new 4 core radiator, but probably need a better shrowd and a better fan. It does get super hot here (was mid 90s today), so I'm curious to see how it does.

Long story short, I'm just not the best at tuning, and the last thing I want to do is blow the thing up after just building it a couple years ago. If running 100 would be safe, that's easy... It's far from a daily driver. But based on tuning knowledge, I probably need a little margin for error.
 
Might want to rejet the carb for sea level. might be running lean at sea level with Colorado jets, which won't help with ping. Good luck. Too bad you left Colorado but at least you went to Texas and not CA!
 
93? Adjust the timing.

You'll need an 8 blade water pump to move the coolant at lower rpms so you don't get any hot spots. Also you'll need a fan spinning at low rpm and idle, not so much at speed, so either a good flex 18 inch or better if no shroud.
 
Disagree with the flex fan. Get the MoPar viscous 5 blade fan. Best unit you'll ever use. Use with the
Proper shroud.

Jet richer for sure.
What carb do you have specifically?
Do you know how to read a spark plug?
A "02" sensor w/gauge can help a lot.
 
MOPAROFFICIAL said:
93? Adjust the timing.

You'll need an 8 blade water pump to move the coolant at lower rpms so you don't get any hot spots. Also you'll need a fan spinning at low rpm and idle, not so much at speed, so either a good flex 18 inch or better if no shroud.
Click to expand...

It posted before I finished typing.

...Or a smaller clutch fan with a shroud.
 
I would just try the highest they have at the pump. If it works, back off to the next lower. Do this until it doesn't work anymore. Definitely rejet the carb first.
 
my guess is it will run fine with 91 go down 2 heat ranges with your plugs rejet and timing .
 
I do have an O2 sensor and gauge, and a high flow water pump. Will look into a new fan and shrowd and possibly a 6 pack hood scoop to get cooler air intake.

So you guys think I'll be safe running 93 octane gas with 10.2:1 compression and iron heads, with 280 duration cam assuming I can keep it cool?

I've got pretty loud exhaust. Is it possible to not hear the pinging? Is there a good way too test?
 
I ran a similar combo in a 4 door valiant for several years as my daily driver. It never pinged on 92, but would on 87 if I ran it hard. I had the MP 280 .474 cam 10.5-1 home ported j heads. Gearing was usually 323 or 355. We are about 500' above sea level here.
 
Mopar Sam said:
I ran a similar combo in a 4 door valiant for several years as my daily driver. It never pinged on 92, but would on 87 if I ran it hard. I had the MP 280 .474 cam 10.5-1 home ported j heads. Gearing was usually 323 or 355. We are about 500' above sea level here.
Click to expand...
Did it run cool?
Looks like the MP280 cam has slightly more duration at .050 lift 238 vs 230. Not sure if that makes a big difference.
Maybe I'm more concerned than I need to be. I had always heard 10:1 or higher was dangerous with open chamber iron heads.
 
Dangerous? No, you just have to pay attention to timing etc. I ran 10.2:1 SCR on a short duration cam for about 95k miles way back in the 70's-80's. Had to not go high on total timing and ran premium. Wore the engine out with that.

BTW, a cool, dry fall day is the biggest challenge; dense air and no humidity to moderate the combustion process. So you are at a good time of year to work on this.
 
I had a 4 row radiator with an electric fan and it ran cool. I was working construction and p.t a lot of miles on it. At the time it was our only vehicle. 100 plus miles a day and a lot of 6 day weeks. I roe it in winter and the brutal summer heat. Ran it almost 6 years that way. I had kb107 pistons and had rhoads lifters on that 280 cam, so it acted smaller at lower revs. Over the years i have learned not to fear a little compression.
 
Dana67Dart said:
Might want to rejet the carb for sea level. might be running lean at sea level with Colorado jets, which won't help with ping. Good luck. Too bad you left Colorado but at least you went to Texas and not CA!
Click to expand...
So far I'm a fan of TX. They will let me register as a classic which is emissions exempt, vs Colorado where I was one year off (76 vs 75). I used to live in highlands ranch and had to get creative to keep it registered.
 
rumblefish360 said:
Disagree with the flex fan. Get the MoPar viscous 5 blade fan. Best unit you'll ever use. Use with the
Proper shroud.

Jet richer for sure.
What carb do you have specifically?
Do you know how to read a spark plug?
A "02" sensor w/gauge can help a lot.
Click to expand...
I'm running an Edelbrock 650 which might be a bit small, but my Holley 750 vac secondary has a flat spot at part throttle (lean per O2 sensor) and I don't want to risk it with the high compression.
 
jimjimjimmy said:
my guess is it will run fine with 91 go down 2 heat ranges with your plugs rejet and timing .
Click to expand...
I was just running standard spark plugs. Does the spark plug heat range really play that big a part in detonation?
 
Mopar Sam said:
I had a 4 row radiator with an electric fan and it ran cool. I was working construction and p.t a lot of miles on it. At the time it was our only vehicle. 100 plus miles a day and a lot of 6 day weeks. I roe it in winter and the brutal summer heat. Ran it almost 6 years that way. I had kb107 pistons and had rhoads lifters on that 280 cam, so it acted smaller at lower revs. Over the years i have learned not to fear a little compression.
Click to expand...
Interesting. I guess you need to take a grain of salt with everything you hear on the forums. From what I read 9.5 was the limit for open chambered iron heads and medium cam. I'll give it a shot as is with a better radiator fan and hopefully a closed air system hood scoop with race gas/ premium gas mix and just keep lowering the octane until it becomes an issue...
 
Keep in mind it gets brutal hot in TX in the summer.
90 deg F is nothing, I have a friend that lives there, his garage is air conditioned, and he says some times it is too hot to even get in the pool.
 
SBM4theW!n said:
I was just running standard spark plugs. Does the spark plug heat range really play that big a part in detonation?
Click to expand...

Yes it is typical in supercharged cars to drop 2 heat ranges to keep out of detonation.
 
Leadfoot said:
I would just try the highest they have at the pump. If it works, back off to the next lower. Do this until it doesn't work anymore. Definitely rejet the carb first.
Click to expand...
Both of my 340s are 10:1 J head motors, one is 268 the other 274 cam. My 67 is street/strip with an aggressive ignition curve 27*/34* and runs great on 93. The 73 is street only and runs on 89 with the 268 cam. A good tune is important, you check for detonation with a magnifying glass and look for specks on the porcelion. Run it on mechanical timing only first, then add the vacuum advance and dial mid to upper 40s for cruise. I use ported on the VCAN. I run MSD 6AL boxes and Autolite copper core 65s at .035 gap. A good phenolic spacer also helps to keep the carb cooler. Both cars have functioning sealed dual snorkel scoops for fresh air.
 
SBM4theW!n said:
I was just running standard spark plugs. Does the spark plug heat range really play that big a part in detonation?
Click to expand...


Yes it does.

I run 11.01:1 on iron heads with pump gas. I have more cam than you do and 4.56 gears but with the correct tune up you should be pooping in tall cotton.
 
mderoy340 said:
Both of my 340s are 10:1 J head motors, one is 268 the other 274 cam. My 67 is street/strip with an aggressive ignition curve 27*/34* and runs great on 93. The 73 is street only and runs on 89 with the 268 cam. A good tune is important, you check for detonation with a magnifying glass and look for specks on the porcelion. Run it on mechanical timing only first, then add the vacuum advance and dial mid to upper 40s for cruise. I use ported on the VCAN. I run MSD 6AL boxes and Autolite copper core 65s at .035 gap. A good phenolic spacer also helps to keep the carb cooler. Both cars have functioning sealed dual snorkel scoops for fresh air.
Click to expand...
That's the first time I've considered the vacuum advance coming into the equation. I figured it only upped the timing where there was little to no load, which is usually a safe zone for detonation. Is that not the case?

Plugging up the hose is super easy, just trying to better understand the science here.
 
sireland67 said:
Yes it is typical in supercharged cars to drop 2 heat ranges to keep out of detonation.
Click to expand...
So what heat range/ plug should I be looking at? I didn't do much research when purchasing the original plugs so I wouldn't trust my starting point.
 
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