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Discussion Starter · #1 ·
I'm still finishing up a few things, but I got the new Summit 600 installed on my 71 351 Mach 1, the carb fit great, started right up, idle is fine, only needed a small choke adjustment, I'm very pleased with it so far. I still have to trim the carb stud, wire the electric choke, reroute some plug wires and add some race fuel before I can take it for a test drive. A funny thing happened after the carb install, I opened the throttle real quick by a hand a few times ( because that's what I do) and heard what I thought was detonation, and then I thought damn, that's the worst detonation ever? Well I quickly decided it was something hitting somewhere on the car, but working by myself
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it was hard to make the noise happen and try and locate it, and my hearing is just about shot. I was right on track to blaming a broken motor mount that was causing the exhaust to hit the body, when I discovered it was coming from the hood area. It was the ram air flaps opening and banging shut, yeah I felt pretty stupid, but glad it nothing needed repair.
 

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A nice review, but, I "Second" the question.
 
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Doesn't this engine have 11 to 1?
Have you verified your timing is in specs? Maybe a "Boss 351" had 11 to 1, but, a standard 351 was 9.0?
 

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Discussion Starter · #6 ·
Have you verified your timing is in specs? Maybe a "Boss 351" had 11 to 1, but, a standard 351 was 9.0?
I set timing the initial timing, probably need to see what the total is, I've owned the car for 2 years and have only driven it about 50 miles, trying to get some miles on it now. From what I've read, the advertised compression on a 71 351 M code is 10.7 to 1, I know my 70 351 Mach 1 had to have good fuel, which was still available when I owned that car in the seventies.
 

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........the advertised compression on a 71 351 M code is 10.7 to 1
Yup, if that's what it is in reality it's a rare one. A one year only deal. 285hp with 10.7:1
 

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Discussion Starter · #8 ·
Yes, it's a 1971 351 M code Mach 1 with factory installed ram air, PS and C6, it has 72,000 original miles, not a bad car, but not a restored one either. I assumed the high compression, left over M code engines from 1970 made their way into the 71 models?
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The only Cleveland to get 11:1 compression from the factory was the Boss 351. Those had popup pistons. (And it probably wasn't really a full 11:1.)

The 1970 Cleveland M-Code was advertised at 10:1 static compression. It was really 9:1. It's extremely unlikely your Cleveland static compression is higher than 9:1. My Cleveland has about 10.7:1 but that's because it has Aussie heads. I run premium pump gas with no detonation/pinging issues.
 

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Nothing wrong with running race fuel, I run ethanol free 92 or 93 and my static compression is about 10.9:1. 10% ethanol blend fuel is what I can get at the pump around me and I won't run it in anything that sits for the winter. The mustang, the lawnmower and the rototiller get the good stuff. I'm over finding crystal sculptures in my carb bowls.
 

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70 M code was advertised as 11.0:1 w/63cc heads
71 M-code was advertised as 10.7:1 w/67cc heads

When you calculate it out, the 70 comes out to between 9.7:1 and 10.1:1, depending upon which head gasket thickness you use. The 71 calculates out to 9.3:1 to 9.7:1. Either way, Ford overstated the compression ratio by about a full point. It is physically impossible to attain the advertised ratios the way they were built.
 

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70 M code was advertised as 11.0:1 w/63cc heads
71 M-code was advertised as 10.7:1 w/67cc heads

When you calculate it out, the 70 comes out to between 9.7:1 and 10.1:1, depending upon which head gasket thickness you use. The 71 calculates out to 9.3:1 to 9.7:1. Either way, Ford overstated the compression ratio by about a full point. It is physically impossible to attain the advertised ratios the way they were built.
Where are seeing the '70 M-code at 11:1? I believe you, I've just never seen it. And I'm still skeptical. And I completely agree about Ford overstating their compression ratios.

While running race fuel won't hurt anything, it's crazy expensive and, if the engine isn't really high in compression, it won't help anything either. It's just flushing money out the exhaust pipe for no reason.
 

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Discussion Starter · #14 ·
Update! The Summit carb ended up having issues, so I had to send it back. The throttle was always stiff with or without the throttle cable, choke on or off and wanted to stick at 1200 RPM. I was in the process of adding a return spring, when I noticed a short stream of fuel shooting out at the throttle shaft bore on the driver's side, happened every time the throttle was opened. The shipping carton was perfect, so can't blame UPS on this one, I'd say mismachined throttle bore, but more than likely dropped at some point before shipping it to me.
 
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