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If cam timing/ intake valves close at 69* ATDC will I be safe running 93 octane in my 406 sbc? My buddy is selling a set of sportsman II's that have really been worked on good, excellent valves and springs for my combo, and a vic jr. that is port matched to the heads. I could save some dough by going with these but want to make sure this combo will work okay on 93 octane.
 

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I come up with a DCR of 8.366:1. That's near the upper end of "pump gas friendly" but not beyond. Knock the edges off the chambers and piston tops, and get a good quench number and it will be ok.
 

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I come up with a DCR of 8.366:1. That's near the upper end of "pump gas friendly" but not beyond. Knock the edges off the chambers and piston tops, and get a good quench number and it will be ok.
From the Kelly discussion, I was under the impression that .035 to .045 was the ideal quench range?
 

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I come up with a DCR of 8.366:1. That's near the upper end of "pump gas friendly" but not beyond. Knock the edges off the chambers and piston tops, and get a good quench number and it will be ok.

Jim, would you tell me the same if my ABDC was 67* and a 8.6 DCR? My little octane program tells me I need 98 octane at worse case 500 ft altitude. I can go to thicker gasket but my quench get up to .060. Still juggling this.
 

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Jim, I am going through the same calculation with a 350 we have just trying to put it together with some stuff we have extra. How did you calculate the dynamic compression with only the intake valve closing event(opps sorry I missed the CR even so would you need the rod ratio)? Could one also install the cam slightly retarded like 4 degrees and lower the dynamic compression?
 

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KGRIFF, I just put in bore n stroke for a 406, and ballparked everything else to get the stated 10.75:1 static.

While PatK's s/w can calculate intake close from full cam specs, it also allows you to simply type it in, so I did.

Dave, the stated (by the poster) .039" is between .035-.045, or were you responding to another of my posts? I do personally consider tighter to be better, and .030" to be "safe" in a steel rod motor that's not revving to the moon.

Don, 8.6 is up there. Won't say it can't work, and have read some that have said it has. IK have no real experience with very high DCR's since I was young and stupid and didn't know any better.

Best case, I think it can work. I would not sacrifice quench for a marginally lower static comp. Go for 040-045. Smooth the heck out of the chambers and piston tops, polish them even. run cold plugs, cold as will not foul. EFI and computer controlled timing would be great for this, never goes lean and can automatically back out some timing when conditions get right for detonation.

The "light throttle, tall gear, low rpm, high load" detonation scenario is right where many hipo engines have a lot of mechanical advance and a lean spot in the carb.

It would be fun to figure the DCR in a "too much compression" 400 I built many years ago. Anyone know the specs on a Crane "Blazer" cam from around 1979? The rest I remember.
 

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I wonder if these DCR calculator recomendations, 8.4 being the upper limit for 93 octane, are for iron headed engines or aluminum? I have a old blazer cam to I think it was .44? lift but I lost the spec card .
 

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Jim,

My 1975 Midwest Auto cat. lists three Crane "Fireball" cams that I think just might have turned into the "Blazer" line, but I can't verify it??

Fireball 286 hy-cam; 31/75, 75/37 and is advertised at 286/292, .450" lift.

Fireball 296 hy-cam; 34/82, 82/34 and advertised duration is 296, .449" lift.

Fireball 314 solid cam; 47/87, 97/37, and advertised duration of 314/?, and .443" lift.

Not much to go on??

pdq67
 

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iron, alumiinum, ceramic, brass, copper, it doesn't matter what the head is made of.
The water in the jackets is 180*
The flame front in the cylinder is nearly constant at 6,000 rpm (50 flames per second)
 

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iron, alumiinum, ceramic, brass, copper, it doesn't matter what the head is made of.
The water in the jackets is 180*
The flame front in the cylinder is nearly constant at 6,000 rpm (50 flames per second)
I think the issue is how efficiently the heads transfer heat to that 180 degree water. The general consensus is that aluminum heads transfer heat more efficiently than cast iron heads, and that you can generally run a higher DCR with aluminum heads than you can with cast iron.

JimM may be absolutely correct that an 8.366:1 DCR will be fine for a properly prepared iron headed engine; however if it were mine, I'd be looking for some way to reduce the DCR. Even if everything else is set, a different cam could help a lot.
 

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Jim,

My 1975 Midwest Auto cat. lists three Crane "Fireball" cams that I think just might have turned into the "Blazer" line, but I can't verify it??

Fireball 286 hy-cam; 31/75, 75/37 and is advertised at 286/292, .450" lift.

Fireball 296 hy-cam; 34/82, 82/34 and advertised duration is 296, .449" lift.

Fireball 314 solid cam; 47/87, 97/37, and advertised duration of 314/?, and .443" lift.

Not much to go on??

pdq67
The cam I had was MUCH milder than any of those. The "fireball" was the next series up from "blazer."
 

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Jim,

72LT1 over on Team Chevelle came back with this.

This cam was bought in 1980 and installed in a 350 at the time. I'll give you all I have.

Advertised valve timing Intake opens 30 BTDC closes 78 ATDC
Exhaust opens 78 BBDC closes 30 ATDC

Advertised duration Intake 288 Exaust 288 overlap 60 degrees

Cam lobe lift .300 Intake .300 Exhaust
Theoretical valve lift based on 1.5 is Intake .450 Exhaust .450

Cam timing at .050 Intake opens 0 BTDC closes 38 ABDC
Exhaust opens 48 BBDC closes -10 BTDC

Duration @ .050 Intake 218 Exhaust 218

Lobe centerline 114

That is straight from the cam sheet he kept from the box.

pdq67
 

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That does sound like the cam... slow lazy lobes, not much lift, real short 050 numbers. In the 400, she idled like a caddy at about 400 rpm, and was way out of steam at 5500.

The motor I built 20 some years ago when I was young and stupid worked out to 11.53: static comp w/ double hump 64cc heads and flat 4 eyebrow pistons.

I just calculated the DCR at 8.84!! That explains a LOT.

This was back in the late 70's. They had just phased out leaded premium but we could still buy leaded regular (87 octane) The "trick of the day" was to mix leaded reg and unleaded premium 50/50. Said to give an octane number around 94-95.

This darned 400... I spent an entire summer tuning her with a tach and a vac gauge and a lot of plug readings. Put in an edelbrock electronic water injection setup, and played with jets and power valves and PVCR's and timing and water setings for months. I finally DID get it to run good and never ping tho. That beast ran 13.20' & 108 with a pegleg rear and street tires, and later I had it in a 4 speed 69 vette. That car could pull up the 6% grade in front of my house from a dead stop in fourth, no throttle, no clutcj slipping, she'd just chug right up that hill!

Damned thing ate starters for lunch, cranking comp was WAY up there.
 

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Jim,

HOGDADDY over on Team Chevelle also posted these just now.

Here ya go: Blazer cams

int. exh. int. exh.

278 278 467 467

300 300 465 465

300 300 480 480

310 310 500 500


pdq67
 
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