Making power with an 8.1
03-08-2005, 11:32 PM
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Making power with an 8.1 How much of a difference does a low compression ratio make then a higher one? Like...how much power are you loosing by going 9.0:1 instead of 10.50:1. Two of my friends have some projects in the works.
First friend has a 2002 Chevy 2500HD with an 8.1. I got to say, I'm amazed at the parasitic loss his truck suffers (I'm sure it's all because of the heavy duty rearend) but it only put down 264 hp and 320 lb/ft at the wheels. He wants to get more power out of it and is wondering what his options are. He has an old 454 91 SS truck that is currently not running that he had some work done, and was wondering if anything is interchangeable. I have heard little bits here and there that the 8.1 is an offshoot of the old BB 454. Is that true? I told him he should maybe just put a blower on there like a Magnuson but he wants to do it on motor and says he can save money that way. I haven't heard of very many companies offering aftermarket heads for the 8.1, so I was hoping the 454 was interchangeable. I know it isn't related to the LS family. If he wants to make a lot of power, should he raise the compression or keep it stock? Gas cost is kind of an issue but he'd rather have more power then economy. Would it be a big enough difference to go with higher compression pistons? How would fuel economy be affected? What are some good cam combos? He wants to make a lot of power...should I go with a bit of a narrow LSA with high duration? Do you think a lot of overlap is a good or a bad thing? Smog is not an issue, no testing here really.
Second friend has a 75 Chevy 1/2 ton with a 400 backed by a TH400. I have heard to be careful with these blocks, that it's easy to crack the cylinder walls with not all that much of an overbore? Anyway, he wants to rebuild his motor with a .020 overbore in mind and we're thinking about putting some Vortec 350 heads on there, not sure of what cam to go with. I've never worked on a Chevy 400 nor am I very familiar with them but my understanding is that its a 350 with a 454 crank I think? Well any info on the 400 would be much appreciated.
Just would like to know, how big of a difference does the compression ratio make for making power? How much power do you gain/loose by raising/lowering the compression?
First friend has a 2002 Chevy 2500HD with an 8.1. I got to say, I'm amazed at the parasitic loss his truck suffers (I'm sure it's all because of the heavy duty rearend) but it only put down 264 hp and 320 lb/ft at the wheels. He wants to get more power out of it and is wondering what his options are. He has an old 454 91 SS truck that is currently not running that he had some work done, and was wondering if anything is interchangeable. I have heard little bits here and there that the 8.1 is an offshoot of the old BB 454. Is that true? I told him he should maybe just put a blower on there like a Magnuson but he wants to do it on motor and says he can save money that way. I haven't heard of very many companies offering aftermarket heads for the 8.1, so I was hoping the 454 was interchangeable. I know it isn't related to the LS family. If he wants to make a lot of power, should he raise the compression or keep it stock? Gas cost is kind of an issue but he'd rather have more power then economy. Would it be a big enough difference to go with higher compression pistons? How would fuel economy be affected? What are some good cam combos? He wants to make a lot of power...should I go with a bit of a narrow LSA with high duration? Do you think a lot of overlap is a good or a bad thing? Smog is not an issue, no testing here really.
Second friend has a 75 Chevy 1/2 ton with a 400 backed by a TH400. I have heard to be careful with these blocks, that it's easy to crack the cylinder walls with not all that much of an overbore? Anyway, he wants to rebuild his motor with a .020 overbore in mind and we're thinking about putting some Vortec 350 heads on there, not sure of what cam to go with. I've never worked on a Chevy 400 nor am I very familiar with them but my understanding is that its a 350 with a 454 crank I think? Well any info on the 400 would be much appreciated.
Just would like to know, how big of a difference does the compression ratio make for making power? How much power do you gain/loose by raising/lowering the compression?
03-08-2005, 11:55 PM
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try posting this question on the board at hotrodders.com (engine section). There are a lot of people with older style blocks squeezing the last hp out of them :-) ls1tech board is great with a lot of nice knowledgeable people, but your question will get more responses on the other one. good luck!
03-09-2005, 09:54 AM
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Originally Posted by transamman400
He has an old 454 91 SS truck that is currently not running that he had some work done, and was wondering if anything is interchangeable.
03-09-2005, 11:13 AM
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I'd have to search for it but I heard only a few things are interchangeable. I think the 8.1 is roughly based on the GEN VI design, I think the 454 ss is an IV. I could be wrong.
A lot of power can be gained with tuning the 8.1. Torque management is very present. In some cases at WOT in 1st gear the electronic throttle will only open to 60% even when you have it floored. There's a larege etc table with a bunch of values. making them all read 000000 should net a large gain and 100% tps when your at WOT
A lot of power can be gained with tuning the 8.1. Torque management is very present. In some cases at WOT in 1st gear the electronic throttle will only open to 60% even when you have it floored. There's a larege etc table with a bunch of values. making them all read 000000 should net a large gain and 100% tps when your at WOT
03-09-2005, 11:37 AM
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I think you're right... 8.1 Gen VI. I think the '91's might have been the Gen IV's.
Cracks me up...they put a lot of effort into that engine and it ends up in like two vehicles.
Cracks me up...they put a lot of effort into that engine and it ends up in like two vehicles.
