compression pistons
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Cross-Country
Joined: Oct 2019
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compression pistons
Hello fellow FTE's
I'm preparing to buy a rotating assembly for my 460. Have a set of 95cc cylinder heads and want a final compression ratio of about 10:1. Unfortunately, most advertised compressions are either 9.5:1 or somewhere in the 11:1 range, nothing in between. I'm wondering approximately how much HP I'd be giving up per point on a 557 build? Anyone know the math equation for this? I'v been told it's somewhere in the 4% range, so I'm thinking approx. 23HP loss on this build, but don't know for sure. 23HP I can live with as I am planning on a later nitrous setup anyway. Any information you all have is greatly appreciated!
I'm preparing to buy a rotating assembly for my 460. Have a set of 95cc cylinder heads and want a final compression ratio of about 10:1. Unfortunately, most advertised compressions are either 9.5:1 or somewhere in the 11:1 range, nothing in between. I'm wondering approximately how much HP I'd be giving up per point on a 557 build? Anyone know the math equation for this? I'v been told it's somewhere in the 4% range, so I'm thinking approx. 23HP loss on this build, but don't know for sure. 23HP I can live with as I am planning on a later nitrous setup anyway. Any information you all have is greatly appreciated!
Cargo Master
Joined: Nov 2009
Posts: 2,364
Likes: 117
From: starship enterprise
nitrous doen\sn't like/need high compression if you want a lot of dope don'trun lots of compression, If you plan on a little dope and mostly motor mage sure you get that compression up to or over 10. problem is less than 10 you want to not go big on cam or it won't run. so milder all the way but that gets "doggy" in my experience meaning it isn't snappy, it isnt fast its more stockish in characteristic.I would shoot for 10+ or just spray the tar outof it.
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Cross-Country
Joined: Oct 2019
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Thanks F-250 WARHORSE, The engine will be 557cid with a roller cam I saw on PowerNation build. A company emailed me that they have -22cc pistons(dished) that will give me 10.11 compression with a .040 gasket. As for the nitrous, Backing off the timing 4degrees per 100HP boost will keep me from detonating on the laughing gas. Also planning on using a limiting switch on it to keep the bottle only for mid-range-upper PRM. Running a spray bar set-up with 150-300 HP boost variable jetting. Spending GOBS of $$ on a 4340 forged crank, H-beam rods w/ stronger bolts, and forged pistons. Setting ring gaps for nitrous, but using total seal top and second rings, and using colder plugs. Figure at 10+ to 1, it should be peppy enough off the bottle, while having fun on the weekends with this set-up should yield around 1000HP on the funny gas. Thank you for your help! It's nice to finally get a response from someone. Isn't anyone else building 460's anymore for fun times!? My neighborhood seems to be inundated with "rice rocket" Hondas and Subarus! So sad these kids haven't had a chance to see real HP.
Fleet Mechanic
Joined: Sep 2016
Posts: 1,459
Likes: 70
From: Southern Maryland
What octane are you planning to use for this build? With the giant bore I would expect it to have detonation problems with a compression ratio of 10:1 on pump gas, but I have never built a big block 385 engine before, so that's just my speculation. I'm planning on a 454 build using a 370 truck block bored to 4.1 with a 4.3 stroker crank and 95 CC aftermarket aluminum heads to put in my '76 F250. The reason I'm going through all that trouble is because I want to be able to run on pump gas and get 12 mpg on the freeway (I'll settle for 10). Compression will end up right at 9:1 with flat tops. I'm not looking for high HP, but I want the torque peak to be close to 500 below 5K. I'm going to need custom pistons, so I could bump the compression up if needed, but I don't want to risk making it require race gas.
It sounds like you've built a big block Ford before. What was your experience with compression vs pump gas requirements?
It sounds like you've built a big block Ford before. What was your experience with compression vs pump gas requirements?
Lead Driver
Joined: Mar 2004
Posts: 8,922
Likes: 153
What octane are you planning to use for this build? With the giant bore I would expect it to have detonation problems with a compression ratio of 10:1 on pump gas, but I have never built a big block 385 engine before, so that's just my speculation. I'm planning on a 454 build using a 370 truck block bored to 4.1 with a 4.3 stroker crank and 95 CC aftermarket aluminum heads to put in my '76 F250. The reason I'm going through all that trouble is because I want to be able to run on pump gas and get 12 mpg on the freeway (I'll settle for 10). Compression will end up right at 9:1 with flat tops. I'm not looking for high HP, but I want the torque peak to be close to 500 below 5K. I'm going to need custom pistons, so I could bump the compression up if needed, but I don't want to risk making it require race gas.
It sounds like you've built a big block Ford before. What was your experience with compression vs pump gas requirements?
It sounds like you've built a big block Ford before. What was your experience with compression vs pump gas requirements?
More Turbo
Joined: Mar 2019
Posts: 530
Likes: 89
A 460 can run on pump gas with iron heads and a compression of 9.5:1. Higher than that and you'll start running into issues. With aluminum heads you can bump it up another point and be fine with pump gas, maybe even another point and a half. Aluminum dissipates heat much better than iron and this affects what kind of compression you can run. Granted, if you want to tow heavy loads, I wouldn't walk near the edge of detonation with regards to building your engine, but for a cruiser I don't see an issue. I'm not a professional engine builder, but I did stay at a Holiday Inn Express last night.
Fleet Mechanic
Joined: Sep 2016
Posts: 1,459
Likes: 70
From: Southern Maryland
A 460 can run on pump gas with iron heads and a compression of 9.5:1. Higher than that and you'll start running into issues. With aluminum heads you can bump it up another point and be fine with pump gas, maybe even another point and a half. Aluminum dissipates heat much better than iron and this affects what kind of compression you can run. Granted, if you want to tow heavy loads, I wouldn't walk near the edge of detonation with regards to building your engine, but for a cruiser I don't see an issue. I'm not a professional engine builder, but I did stay at a Holiday Inn Express last night.
This is for a truck that will pull an 8K lb trailer across the Appalachians, so it needs a lot of torque to go up the steep grades and not knock. If the 460 is good to go as is, then I'll just throw the parts on it I already have: RV cam, Wieand 8012 intake, Holley 735 cfm carb, aluminum heads and water pump. The F250 rides like a tank, but it's not going to be a daily driver, so I can live with it.
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Cross-Country
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What octane are you planning to use for this build? With the giant bore I would expect it to have detonation problems with a compression ratio of 10:1 on pump gas, but I have never built a big block 385 engine before, so that's just my speculation. I'm planning on a 454 build using a 370 truck block bored to 4.1 with a 4.3 stroker crank and 95 CC aftermarket aluminum heads to put in my '76 F250. The reason I'm going through all that trouble is because I want to be able to run on pump gas and get 12 mpg on the freeway (I'll settle for 10). Compression will end up right at 9:1 with flat tops. I'm not looking for high HP, but I want the torque peak to be close to 500 below 5K. I'm going to need custom pistons, so I could bump the compression up if needed, but I don't want to risk making it require race gas.
It sounds like you've built a big block Ford before. What was your experience with compression vs pump gas requirements?
It sounds like you've built a big block Ford before. What was your experience with compression vs pump gas requirements?
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Fleet Mechanic
Joined: Sep 2016
Posts: 1,459
Likes: 70
From: Southern Maryland
I already have the Wieand 8012 dual plane, several Holley carbs and an RV cam with just a tad over .5 lift both intake and exhaust. I don't think you can compare a small bore FE 390 to the giant bore 429/460, but 10.5:1 on 89 octane is impressive. I would be afraid to try that myself, but it's good to know it can work. I built a 10.2:1, 408 Windsor stroker that destroyed the rings. I blamed it on using 89 octane gas, but the advance may have been too much. They may have also destroyed the rings on the dyno. They set the initial timing at 16 degrees, 36 total to make 537 at 5800. It had excessive blow by as soon as I installed it in my car.
Flame travel on the big bore 385 series takes much longer. Ford reduced compression and retarded timing in the 70s on the big blocks to survive on unleaded fuel which of course killed power. But it's easy to get a lot of that back by simply swapping in an aftermarket cam and installing it straight up. The heads are Chinese knock offs of the Edelbrock 60679 head but they were finished in the US (valve's and springs installed).
Flame travel on the big bore 385 series takes much longer. Ford reduced compression and retarded timing in the 70s on the big blocks to survive on unleaded fuel which of course killed power. But it's easy to get a lot of that back by simply swapping in an aftermarket cam and installing it straight up. The heads are Chinese knock offs of the Edelbrock 60679 head but they were finished in the US (valve's and springs installed).
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