concerned about compression ratio
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New User
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From: Georgia
concerned about compression ratio
I need some advice on a 460 engine I found in a salvage yard. It was in a 1970 Continental. (Yes, D0ve heads, short deck block, 10.5:1 compression ratio)
My question; Can I run 10.5:1 compression on todays premium fuel? I'm worried about detonation. I've been advised to lower the compression to 9.5 by some folks, and others say its ok at 10.5.
I plan on installing a longer duration cam than stock, and generally understand that this will affect the dynamic compression ratio, which will provide a bit of a buffer for detonation.
I've called several cam tech people and havent gotten a satisfying answer.
Anyone......please advise.
Oh....the 460 is gonna be stuffed in my 1977 F-150 4X4, C-6, 3.50 gearing.
Will install headers, aluminum manifold. Thanks.
My question; Can I run 10.5:1 compression on todays premium fuel? I'm worried about detonation. I've been advised to lower the compression to 9.5 by some folks, and others say its ok at 10.5.
I plan on installing a longer duration cam than stock, and generally understand that this will affect the dynamic compression ratio, which will provide a bit of a buffer for detonation.
I've called several cam tech people and havent gotten a satisfying answer.
Anyone......please advise.
Oh....the 460 is gonna be stuffed in my 1977 F-150 4X4, C-6, 3.50 gearing.
Will install headers, aluminum manifold. Thanks.
Elder User
Joined: May 2003
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I run a modified '71 429 in my F-350 with no problems. I use CD-2 lead substitute and 91 octane, non-ethanol off road/collector car fuel in it with no problems. I was running cheap octane booster too, but, I tried it without some and I have not had any problems.
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From: Louisville,Ky.
Limit the advance in the dizzy to keep the total advance down will help. The longer duration camshaft will help also. I know the Erson cams makes special cames for high compression engines to make them run on pump gas. I believe they are called MP1 and MP2, depending on the rpm range you are wanting.
Jimmy
Jimmy
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From: Nevada
A big issue is if you're getting 91-octane or? Modern pumps add octane and some additives at the pump and you could have at least a hose full of 87-octane. And I don't know what emission additives do to octane ratings. Most states add at least 10% of whatever lobby group is in power, from ethanol to MTBE at the refinery. With 11.0:1 c/r, a big cam, which should help with dynamic compression, and aluminum heads, I still have to run 100-octane avgas no matter what I use for advance.
Modern production performance engines can live with variations of fuel, heat and abuse because the management system instantly compensates for detonation problems. Our old iron doesn't have that luxury.
If running pump gas is a concern and you don't want to be constantly messing with the amount of advance or even thinking about it, I'd say use pistons to achieve 9.5:1 c/r. There isn't going to be that big of a power difference between 9.5 and 10.5.
Modern production performance engines can live with variations of fuel, heat and abuse because the management system instantly compensates for detonation problems. Our old iron doesn't have that luxury.
If running pump gas is a concern and you don't want to be constantly messing with the amount of advance or even thinking about it, I'd say use pistons to achieve 9.5:1 c/r. There isn't going to be that big of a power difference between 9.5 and 10.5.
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From: Georgia
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I run 10.5 in my EFI 460 on premium and have no problems. Also you can talk to anybody running restored 429/460 musclecars. The ones I've talked to run premium with no problems with 10.5 CR.
John
John
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Fleet Mechanic
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My D0VE is totally stock, just like it left the factory. Including the ignition system. Cylinder walls and valves are in excellant shape, getting high numbers on a compression test on that one. C6 and 3.0 rear are behind it. And the CD-2 is for lead-less lubrication, CD-2 does not boost octane. Never a ping on 93 octane, though I can't say I've really cooked it in real hot weather.
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What a 10.5:1 can do...
1) The motor: 1971 429 stock bore, head work, and a few other things.
2) The truck: 1979 F-350, DRW, 2wd, 166.5"wb, 12' steel flat bed.
3) The fuel: 91 octane pump gas, non ethanol off road/collector car fuel. It is just plain fuel without ethanol. It is called that becouse it is illegal to use it in newer cars here. I also use CD-2 lead substitute.
4) The story: I was hauling my sleds on a trailer behind the truck 2 nights ago. I decided to stop at BK for a little food. When I pulled in there were some kids there playing with their cars and trucks. As I came back out they were still there playing. I just shook my head at them and smiled. The started laughing at my truck. Well, I decided to show them. I pulled out onto the street and proceded to light the tires up like there was no tomorrow. Hehehe you should have seen the looks on their faces....priceless
. I think a couple of the Chevy drivers may have actually craped their pants. Ford power! Nothing better!
1) The motor: 1971 429 stock bore, head work, and a few other things.
2) The truck: 1979 F-350, DRW, 2wd, 166.5"wb, 12' steel flat bed.
3) The fuel: 91 octane pump gas, non ethanol off road/collector car fuel. It is just plain fuel without ethanol. It is called that becouse it is illegal to use it in newer cars here. I also use CD-2 lead substitute.
4) The story: I was hauling my sleds on a trailer behind the truck 2 nights ago. I decided to stop at BK for a little food. When I pulled in there were some kids there playing with their cars and trucks. As I came back out they were still there playing. I just shook my head at them and smiled. The started laughing at my truck. Well, I decided to show them. I pulled out onto the street and proceded to light the tires up like there was no tomorrow. Hehehe you should have seen the looks on their faces....priceless
. I think a couple of the Chevy drivers may have actually craped their pants. Ford power! Nothing better!
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New User
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From: Georgia
Alrighty.....this is exactly what I was hoping to hear. (I wonder how folks got along without the internet and forums like this!?)
Tell me more about the CD-2 lead substitute. If hardned valve seats are installed, can this be omitted from the fuel? What if its NOT used on old style heads? What happens?
You guys are awesome. Thanks for the info.
Tell me more about the CD-2 lead substitute. If hardned valve seats are installed, can this be omitted from the fuel? What if its NOT used on old style heads? What happens?
You guys are awesome. Thanks for the info.
Postmaster
Joined: Aug 2001
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From: Nevada
The argument between using a lead substitute or having hard exhaust valve seats installed when running unleaded fuel is like different opinions on motor oils.
Over the years I've ran several 429/460s at varying compression ratios with all the cast iron heads and never had hardened seats installed or used a lead additive. Never a sign of exhaust seat erosion in many hard miles on those engines.
Over the years I've ran several 429/460s at varying compression ratios with all the cast iron heads and never had hardened seats installed or used a lead additive. Never a sign of exhaust seat erosion in many hard miles on those engines.
Junior User
Joined: Jan 2001
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My machinist said I should use hardened valve seats if I plan to do a lot of towing. Otherwise he has not seen any problems running without them. So I do not run hraneded seats.
Also he said occasionally cutting the seats can cut into the water jacket, wrecking the head.
John
Also he said occasionally cutting the seats can cut into the water jacket, wrecking the head.
John
Fleet Mechanic
Joined: Sep 2003
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For me, CD-2 is so cheap on a per gallon of gas used cost basis that I won't risk it with mine. CD-2 is a concentrate, one bottle of CD-2 does 320 gallons, IIRC. The plastic bottle has a built-in measuring device, adding it is easy. Walmart has it.
Hardened valve seats will eliminate the need for CD-2. Like I said, I'm not gonna chance it as mine are in excellant condition with low original miles.
Hardened valve seats will eliminate the need for CD-2. Like I said, I'm not gonna chance it as mine are in excellant condition with low original miles.