Increase compression ratio?
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Increase compression ratio?
So, I have an older F250 with the big block 460. I was doing some research and found it had like a 8.5:1 ratio. I was wondering if it would be possible to push that number up maybe to about 9 or so? It's a big block so I would really like to try something with the fuel efficiency
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Welcome to FTE!
You can push it as far as you want, but even a modest increase, other than shaving the heads, will cost more than you'll ever get out of it in MPGs. Shaving a few thousandths off the heads won't get you much and could cause other issues with manifold gaskets and pushrod length.
Swapping pistons will end up as a full rebuild.
What MPG are you getting now? Figure a 20% improvement, which is almost impossible to get without a major overhaul, roller everything etc. Now figure you gas costs at the existing MPG and at 20% better. Can you save some gas? Probably. Can you save money? Probably not.
You can push it as far as you want, but even a modest increase, other than shaving the heads, will cost more than you'll ever get out of it in MPGs. Shaving a few thousandths off the heads won't get you much and could cause other issues with manifold gaskets and pushrod length.
Swapping pistons will end up as a full rebuild.
What MPG are you getting now? Figure a 20% improvement, which is almost impossible to get without a major overhaul, roller everything etc. Now figure you gas costs at the existing MPG and at 20% better. Can you save some gas? Probably. Can you save money? Probably not.
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I'm really not 100% sure what I get to the gallon currently. But I do know it can't be much. I'm sure it's expensive and I'm more than ready to take that into account. I work at an auto parts store so parts and tools aren't much of an issue. If I could increase the efficiency by 20% that would be amazing but I'm not expecting too much at all. I've had the truck for a couple years and it's been kind of a project my father and I have been working on. I'm actually hoping to maybe rebuild or replace most of what I can with the truck, but at the moment I want to look at engine overhaul
Fleet Owner
Joined: Oct 2005
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From: Kentucky
IMHO start with the ancillary parts instead of jumping into the engine. Replace the factory torpedo converter with a high flow version. Better yet take a look at Banks Header system to use with a new converter. It's pricey, but the first step to improve the efficiency of moving air through the engine. The factory intake is actually pretty good, after you cut the air horns out.
If you want to add more HP/TQ then take a look at this thread: 1996 F250 460 baseline dyno results and head porting-RESULTS ARE IN!
The OP recently updated that thread with new information for getting a set of his custom ported heads.
Another well known BBF guru is the Mad Porter: Reincarnation High Performance
Just be aware as you start to get past headers/exhaust upgrades the factory EFI system will have a hard time adjusting. An adjustable Fuel pressure regulator may help a little. If you read through Boport's thread you will find the factory 24 lbs. injectors were getting maxed out.
If you want to add more HP/TQ then take a look at this thread: 1996 F250 460 baseline dyno results and head porting-RESULTS ARE IN!
The OP recently updated that thread with new information for getting a set of his custom ported heads.
Another well known BBF guru is the Mad Porter: Reincarnation High Performance
Just be aware as you start to get past headers/exhaust upgrades the factory EFI system will have a hard time adjusting. An adjustable Fuel pressure regulator may help a little. If you read through Boport's thread you will find the factory 24 lbs. injectors were getting maxed out.
Post Fiend
Joined: Apr 2002
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From: Waterloo, Iowa
Have you done a compression test? That's related to CR in the sense it doesn't matter what the compression ratio is, if the pistons/bores/rings are worn it will not give very good performance or efficiency. Worn timing set and stretched chain will tend to cause late valve timing which will also reduce compression and performance.
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I'll have to do a compression test later. Right now I can't get it to start. I'm not getting any fuel to the fuel rails but it's going through the filter. It's been changed out but it got clogged again. Cleaned it out and now it has flow. I'll have to change the fuel system out as well. I can't seem to find where I can get new rails so I'm trying to clean them out. I just don't know how to go about doing it
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I had an engine with heads that needed valve guides, so I had the heads surfaced at the same time. Not cutdown, just made flat again. Great idea? No, not really as doing that made the rings start leaking...…. massive plug fouling followed..... That engine had about 140 k miles on it. I had to rebuild it to use it....And it was a great engine after that, lasted many years.
I was told not to have the heads resurfaced as it would make the rings leak, but I did not listen. Experience is a great teacher.
I was told not to have the heads resurfaced as it would make the rings leak, but I did not listen. Experience is a great teacher.
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I'll have to do a compression test later. Right now I can't get it to start. I'm not getting any fuel to the fuel rails but it's going through the filter. It's been changed out but it got clogged again. Cleaned it out and now it has flow. I'll have to change the fuel system out as well. I can't seem to find where I can get new rails so I'm trying to clean them out. I just don't know how to go about doing it
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