351 HO question
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351 HO question
Ok...going through the HO 351 in my 1986 f150, I've discovered that the PO replaced the original engine with another 351 from a late 80's Mercury car. Everything else other than the block and the heads is original (still has the 4bbl carb and manifold, etc) My question is, what's the difference between the HO block and heads and a set of non-HO block and heads?
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From: Ottawa, Ontario
Ah.. no.
When talking about the carbed HOs the only difference between them and a plane jane motor is a bigger cam and the 4bbl intake and carb. Everything else.. block, heads, and rotating assembly is the same low compression smog era crap that was everywhere at the time. The HO cam came from the marine engine department and it's pretty close to the later 5.0HO roller cam in lift and duration except that it's a flat tappet grind. The heads on these motors are complete junk.. hugh combustion chambers and tiny valves, and the exhaust systems are even worse. The two single best things you can do to wake one of these old things up is swap on a set of late model heads (E7TE stock production or F1ZE/F3ZE GT40) to get a 1/2 point bump in compression and much better overall airflow, and then drop the whole exhaust including the manifolds and bolt on headers and whatever you like behind it.
P.S. There is nothing at all weak about the block and rotating assembly, it's more than stout enough to handle any upgrade you might want to bolt on top of it.
When talking about the carbed HOs the only difference between them and a plane jane motor is a bigger cam and the 4bbl intake and carb. Everything else.. block, heads, and rotating assembly is the same low compression smog era crap that was everywhere at the time. The HO cam came from the marine engine department and it's pretty close to the later 5.0HO roller cam in lift and duration except that it's a flat tappet grind. The heads on these motors are complete junk.. hugh combustion chambers and tiny valves, and the exhaust systems are even worse. The two single best things you can do to wake one of these old things up is swap on a set of late model heads (E7TE stock production or F1ZE/F3ZE GT40) to get a 1/2 point bump in compression and much better overall airflow, and then drop the whole exhaust including the manifolds and bolt on headers and whatever you like behind it.
P.S. There is nothing at all weak about the block and rotating assembly, it's more than stout enough to handle any upgrade you might want to bolt on top of it.
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Thank you for the info!...unfortunately I'm in California and I can't get away with too many changes like headers...but the heads, would anyone know if I went to the E7TE or GT40 heads would I still pass smog?
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From: Virginia
If you kept it in good tune and kept the original carb and all it's hook ups, it likely would pass with those other heads. You would have to be careful and keep a very mild near stock camshaft in it also.
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Thoughts?
Anybody have suggestions which one of these camshaft a I could get away with and still pass California emissions?
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From: Virginia
"May not be computer compatible" make me suspicious. I don't have any real world experience with those cams but something tells me you need to go milder than those to get a good clean idle. You are not going to pass with the engine sitting there loping with a rough cam in it.
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Actually I think the computer compatible statement is referring to the fuel injected engines of that time. Mine is a carbureted one with no computer. I know the stage 1 is fairly close to stock, I'm just not too sure on the others...
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From: Virginia
I know, the computer can handle very mild cams which is why it makes me suspicious that those are not mild enough for a carbed engine that needs to pass smog. Like I said though, just reading between the lines, no actual experience on using them.
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From: Virginia
351w always has the same firing order,, no matter if it's ho or not. If someone put in a early 302 camshaft in it, then it will have the 302 non-ho firing order. The 302 camshaft will fit the 351w.
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