Real Compression Ratio Daily driver

[nm9stheham]

FWIW, dynamic compression ratio was known and used long before the 70's.

But you are correct about the cams.... it was not the loss of lead as much as being triggered in the early 70's when the Arab oil embargo hit; prices doubled overnight and fuel availability was pretty sketchy for 6-8 months. Sitting 2 hours in line for 5 gallans was not uncommon. So the hot rodders needed cam like that.

Crane had a series call the HE (hydraulic efficiency) cams that did just that.... looong ramps. I ran one for years in a 351C; 62 or 64 degrees difference between .050" and .005" lift points LOL! That engine was 10.3 SCR, 8.3 DCR, had quench, polished chambers and needed 93 octane fuel with a mild tune... could not put in too much ignition timing too soon. Around 19 mpg at 65 mph with a C4 and 3.08 rear gear, carb set up for lean cruising (old Holley List 6619). Probably 300-325 HP peak. Towed, hauled, daily driver for 95 k miles.

So, 10-10.5 seems like a limit on iron heads WITH careful tuning , for a cam that is typical for a DD. Poor chambers and piston setup is going to limit that to a lower CR number, IMHO and you can get into trouble easily if your tuning is careless or if the fuel is crappy. Some of the US urban area EPA mandated summer fuel mixes fall into my definition of 'crappy'.

[Belgian1979]

I have 10.5 in mine with alu heads and closed chamber (dart alu pro 1 64 cc). No audible knock that I can speak off.

[GARY C]

I did a 350 with an iron 167cc runner head, 67cc D shape chamber, straight plug, flat top 2 valve relief, comp 262xe cam on a 104icl with 1.65 rockers. It had a little over 200 psi cranking pressure, 92 octane pump gas.
Timing curve took a little work but it was 20 initial, about 40 at cruise (adjustable vacuum can on full manifold vac) and 36 at wide open throttle it idled at around 700 rpm with 16.5" vacuum.

[BigBlockMopar]

11.3:1cr on a daily driven 360ci smallblock Mopar.
CompCams XE256.
Propane GAS

[PackardV8]

Blocking the exhaust heat riser and adding a cold air intake can make all the difference on hot days and hard pulls.

jack vines

It'll also kill any fuel economy you might have gained by running higher compression.

We're going to have to agree to disagree on this one. I've been running this setup on dozens of engines over fifty years. Only a few minutes of quicker warmup is lost. Put an O2 sensor in the downpipe and measure the before and after A/F ratio and get back to me on why no exhaust heat and cold air kills fuel economy.

jack vines

[GARY C]

Blocking the exhaust heat riser and adding a cold air intake can make all the difference on hot days and hard pulls.

jack vines

It'll also kill any fuel economy you might have gained by running higher compression.

We're going to have to agree to disagree on this one. I've been running this setup on dozens of engines over fifty years. Only a few minutes of quicker warmup is lost. Put an O2 sensor in the downpipe and measure the before and after A/F ratio and get back to me on why no exhaust heat and cold air kills fuel economy.

jack vines

Not sure how it would hurt economy to properly control the air temp for an engine combo... As far as I know all modern day vesicles have mover away from std heat riser and vent their air boxes to fresh air?

[Ken_Parkman]

IMO there are far too many variables for a simple rule. And the type of use is huge as well. A "street" car that gets driven occasionally is a big difference from a real driver that can get in a traffic jam on a hot day and get stinking hot. Iron head, old technology (spark plug way to the side) stay below 9.5 if you want to really street drive it. Better heads, design, and control you can push it further. My experience has been a properly designed combo for the fuel and application will make more power and work better than purposely mismatching things to use a higher compression than ideal for the fuel.

[nm9stheham]

11.3:1cr on a daily driven 360ci smallblock Mopar.
CompCams XE256.
Propane GAS

LOL.. that's cheating with the propane!

[Roadknee]

It'll also kill any fuel economy you might have gained by running higher compression.

We're going to have to agree to disagree on this one. I've been running this setup on dozens of engines over fifty years. Only a few minutes of quicker warmup is lost. Put an O2 sensor in the downpipe and measure the before and after A/F ratio and get back to me on why no exhaust heat and cold air kills fuel economy.

jack vines

Not sure how it would hurt economy to properly control the air temp for an engine combo... As far as I know all modern day vesicles have mover away from std heat riser and vent their air boxes to fresh air?

Intake heat not needed with port fuel injection. I tuned a vortec headed 10:1 355 in a 1995 TBI truck. The amount of acceleration enrichment it needed was insane, and changed with the weather.

[GARY C]

IMO there are far too many variables for a simple rule. And the type of use is huge as well. A "street" car that gets driven occasionally is a big difference from a real driver that can get in a traffic jam on a hot day and get stinking hot. Iron head, old technology (spark plug way to the side) stay below 9.5 if you want to really street drive it. Better heads, design, and control you can push it further. My experience has been a properly designed combo for the fuel and application will make more power and work better than purposely mismatching things to use a higher compression than ideal for the fuel.

Mine was a "street" car built as a daily driver, 1000 over stock converter, 273 gear and a 28" tire to keep rpm low, where I live to most places I need to go is a 45 minute drive and I needed a light duty truck for material for my business and my supplier is 60 miles from me, through Dallas Tx traffic.

My research and experience told me that this combo would do what I needed, run good on pump gas less than 93, haul material, smoke both back tires as far as the eye could see... all while jamming to YYZ.

You know it's good when reality rimes I will say the budget 1000 watt amp for my stereo was a Kraco/Sparkomatic 50 watt at best. Youngens may not get that.

[GARY C]

We're going to have to agree to disagree on this one. I've been running this setup on dozens of engines over fifty years. Only a few minutes of quicker warmup is lost. Put an O2 sensor in the downpipe and measure the before and after A/F ratio and get back to me on why no exhaust heat and cold air kills fuel economy.

jack vines

Not sure how it would hurt economy to properly control the air temp for an engine combo... As far as I know all modern day vesicles have mover away from std heat riser and vent their air boxes to fresh air?

Intake heat not needed with port fuel injection. I tuned a vortec headed 10:1 355 in a 1995 TBI truck. The amount of acceleration enrichment it needed was insane, and changed with the weather.

So you are saying "Intake heat not needed with a proper tune"? I would agree... Just curious, have you ever ran a well tuned Q Jet with a properly set choke?

[Roadknee]

[/quote]
So you are saying "Intake heat not needed with a proper tune"? I would agree... Just curious, have you ever ran a well tuned Q Jet with a properly set choke?
[/quote]

Gary - I think you’re interpreting what YOU want. I never said what you included in quotes above. If you want to believe that go right ahead. I respectfully disagree.

The TBI truck ran great in the Ely, MN summer and fall weather but once winter hit it was another story. I have ran a well tuned qjet. I daily drove a 78 Caprice about 20 years ago. Picked it up with 39k original miles. Every morning pump the throttle twice and it fired immediately and ran on choke at a smooth 1000 rpm idle. Car ran flawlessly whether it was 0 or 100 degrees. It did have a heated intake and thermostatically controlled air cleaner.

[GARY C]

So you are saying "Intake heat not needed with a proper tune"? I would agree... Just curious, have you ever ran a well tuned Q Jet with a properly set choke?
[/quote]

Gary - I think you’re interpreting what YOU want. I never said what you included in quotes above. If you want to believe that go right ahead. I respectfully disagree.

The TBI truck ran great in the Ely, MN summer and fall weather but once winter hit it was another story. I have ran a well tuned qjet. I daily drove a 78 Caprice about 20 years ago. Picked it up with 39k original miles. Every morning pump the throttle twice and it fired immediately and ran on choke at a smooth 1000 rpm idle. Car ran flawlessly whether it was 0 or 100 degrees. It did have a heated intake and thermostatically controlled air cleaner.
[/quote]
Just trying to figure out what your saying, in one post it sounds like your against heat riser and in another you say it's not needed, my personal experience is it's just 2 different tunes and cold winter months would be the only drastic game changer without heat riser but one for a minute or 2.

I am looking at this from a performance tech perspective, not an EPA numbers perspective.

[BigBlockMopar]

11.3:1cr on a daily driven 360ci smallblock Mopar.
CompCams XE256.
Propane GAS

LOL.. that's cheating with the propane!

Cheating with a 'lesser' fuel!
I always thought Americans considered propane as BBQ-fuel...

[peejay]

Blocking the exhaust heat riser and adding a cold air intake can make all the difference on hot days and hard pulls.

jack vines

It'll also kill any fuel economy you might have gained by running higher compression.

We're going to have to agree to disagree on this one. I've been running this setup on dozens of engines over fifty years. Only a few minutes of quicker warmup is lost. Put an O2 sensor in the downpipe and measure the before and after A/F ratio and get back to me on why no exhaust heat and cold air kills fuel economy.

jack vines

Any time I have eliminated manifold heat, I found that I needed more accelerator pump, because more fuel was wetting out on the intake manifold. That's where the economy goes away.