Help: 350 Compression Ratio
Question:
You should be OK with that c.r. Just watch your base timing and go with felpro blues.
Response:
the origonal compression ratio in your 5.7 truck engine was 9.3:1.
Response:
Nope, 8.3. There was a different RPO that had 9.3.
– Hide quoted text — Show quoted text -> the origonal compression ratio in your 5.7 truck engine was 9.3:1.
Response:
Yeah, you’re right, but I had to change the pistons anyway since we bored the block. Actually, the difference is 1.5:1, going from 8.3 to 9.8 that’s why I’m a little worried about 87 octane. I was hoping someone out there was running 9.8 or higher and using 87 octane fuel. Ken
– Hide quoted text — Show quoted text -> Honestly, I don’t think that you are going to gain all that much with the > higher compression ratio (with the difference being .1-.3) to justify the > pain it will be for a regular rig (non-race vehicle). Yeah, you’ll loose a > bit of power, but there are other places to make that up that are easier to > deal with than the combustion chamber. Ported and polished heads will make > a much larger difference than that small compression difference. A free > flowing intake and exhaust system will more than make that up. A simple > chip upgrade if your truck is computerized will do it. And with any of > those other modifications, you can still run regular pump from the > backwoods. > Big Chris > | Yep, it’s got the knock sensor. I don’t mind running supreme gas I just > | don’t want be limited to it. If I end up somewhere in the back country > | needing gas and all the gas station has is regular I want to be able to > use > | it. > | > | Thanks > | Ken R. > | > | > | > You are right on the edge, with that comp., really shold use 91 or > better, > | > if your efi has a knock sensor, you could run 87, but loose some power. > | > > I have a questions I’m hoping someone can answer based on > experience…. > | > > > | > > I have a 1989 GMC Sierra K1500 4×4 that currently has a 305cid engine. > I > | > was > | > > in the right place at the right time and was given a 1994 350cid > engine > | > > (140,000km) that came out of a truck identical to mine except newer. > | Since > | > > the oil pressure on my 305 is getting on the low side (165,000km) I > was > | > > planning to rebuild it soon anyway, so instead we are building the 350 > | to > | > > replace the 305. > | > > > | > > The cylinders on the 350 were a couple thousands out of spec so we > | decided > | > > to bore the block 0.030" oversided and buy new pistons. Before the > | rebuild > | > > we calculated the compression ratio to be around 8.3 to 8.5:1 (stock). > | The > | > > high-output versions of the 350 have a ratio of 9.5:1. We decided to > | boost > | > > the compression ratio by buying the high-output pistons. Now we > | calculate > | > > the compression ratio to be somewhere between 9.6 and 9.8:1 > (estimating > | > the > | > > deck height since the pistons are not installed yet). > | > > > | > > Now my question…will I still be able to run regular unleaded fuel > | > > (Canadian) in this engine? I believe the octane rating of our unleaded > | is > | > 87 > | > > with supreme being 91. I am planning to use my 305’s TBI and > associated > | > > electronics since according to my service manual there is no > difference > | > > except the EPROM which I may replace after testing. If I’m going to > have > | > > trouble with regular unleaded I will install a set of thicker head > | gaskets > | > > to get the ratio down to around 9.5:1 or a little lower. > | > > > | > > Thanks for any advice! > | > > Ken R. > | > > Nova Scotia, Canada > | > > > | > > > | > > > | > > | > > | > > | > > | > —–= Posted via Newsfeeds.Com, Uncensored Usenet News =—– > | > http://www.newsfeeds.com – The #1 Newsgroup Service in the World! > | > —–== Over 80,000 Newsgroups – 16 Different Servers! =—– > | > |
Response:
Honestly, I don’t think that you are going to gain all that much with the higher compression ratio (with the difference being .1-.3) to justify the pain it will be for a regular rig (non-race vehicle). Yeah, you’ll loose a bit of power, but there are other places to make that up that are easier to deal with than the combustion chamber. Ported and polished heads will make a much larger difference than that small compression difference. A free flowing intake and exhaust system will more than make that up. A simple chip upgrade if your truck is computerized will do it. And with any of those other modifications, you can still run regular pump from the backwoods. Big Chris
| Yep, it’s got the knock sensor. I don’t mind running supreme gas I just | don’t want be limited to it. If I end up somewhere in the back country | needing gas and all the gas station has is regular I want to be able to use | it. | | Thanks | Ken R. | | | > You are right on the edge, with that comp., really shold use 91 or better, | > if your efi has a knock sensor, you could run 87, but loose some power. | > > I have a questions I’m hoping someone can answer based on experience…. | > > | > > I have a 1989 GMC Sierra K1500 4×4 that currently has a 305cid engine. I | > was | > > in the right place at the right time and was given a 1994 350cid engine | > > (140,000km) that came out of a truck identical to mine except newer. | Since | > > the oil pressure on my 305 is getting on the low side (165,000km) I was | > > planning to rebuild it soon anyway, so instead we are building the 350 | to | > > replace the 305. | > > | > > The cylinders on the 350 were a couple thousands out of spec so we | decided | > > to bore the block 0.030" oversided and buy new pistons. Before the | rebuild | > > we calculated the compression ratio to be around 8.3 to 8.5:1 (stock). | The | > > high-output versions of the 350 have a ratio of 9.5:1. We decided to | boost | > > the compression ratio by buying the high-output pistons. Now we | calculate | > > the compression ratio to be somewhere between 9.6 and 9.8:1 (estimating | > the | > > deck height since the pistons are not installed yet). | > > | > > Now my question…will I still be able to run regular unleaded fuel | > > (Canadian) in this engine? I believe the octane rating of our unleaded | is | > 87 | > > with supreme being 91. I am planning to use my 305’s TBI and associated | > > electronics since according to my service manual there is no difference | > > except the EPROM which I may replace after testing. If I’m going to have | > > trouble with regular unleaded I will install a set of thicker head | gaskets | > > to get the ratio down to around 9.5:1 or a little lower. | > > | > > Thanks for any advice! | > > Ken R. | > > Nova Scotia, Canada | > > | > > | > > | > | > | > | > | > —–= Posted via Newsfeeds.Com, Uncensored Usenet News =—– | > http://www.newsfeeds.com – The #1 Newsgroup Service in the World! | > —–== Over 80,000 Newsgroups – 16 Different Servers! =—– | |
Response:
Yep, it’s got the knock sensor. I don’t mind running supreme gas I just don’t want be limited to it. If I end up somewhere in the back country needing gas and all the gas station has is regular I want to be able to use it. Thanks Ken R. – Hide quoted text — Show quoted text -> You are right on the edge, with that comp., really shold use 91 or better, > if your efi has a knock sensor, you could run 87, but loose some power. > I have a questions I’m hoping someone can answer based on experience…. > I have a 1989 GMC Sierra K1500 4×4 that currently has a 305cid engine. I > was > in the right place at the right time and was given a 1994 350cid engine > (140,000km) that came out of a truck identical to mine except newer. Since > the oil pressure on my 305 is getting on the low side (165,000km) I was > planning to rebuild it soon anyway, so instead we are building the 350 to > replace the 305. > The cylinders on the 350 were a couple thousands out of spec so we decided > to bore the block 0.030" oversided and buy new pistons. Before the rebuild > we calculated the compression ratio to be around 8.3 to 8.5:1 (stock). The > high-output versions of the 350 have a ratio of 9.5:1. We decided to boost > the compression ratio by buying the high-output pistons. Now we calculate > the compression ratio to be somewhere between 9.6 and 9.8:1 (estimating > the > deck height since the pistons are not installed yet). > Now my question…will I still be able to run regular unleaded fuel > (Canadian) in this engine? I believe the octane rating of our unleaded is > 87 > with supreme being 91. I am planning to use my 305’s TBI and associated > electronics since according to my service manual there is no difference > except the EPROM which I may replace after testing. If I’m going to have > trouble with regular unleaded I will install a set of thicker head gaskets > to get the ratio down to around 9.5:1 or a little lower. > Thanks for any advice! > Ken R. > Nova Scotia, Canada > —–= Posted via Newsfeeds.Com, Uncensored Usenet News =—– > http://www.newsfeeds.com – The #1 Newsgroup Service in the World! > —–== Over 80,000 Newsgroups – 16 Different Servers! =—–
Response:
You are right on the edge, with that comp., really shold use 91 or better, if your efi has a knock sensor, you could run 87, but loose some power.
– Hide quoted text — Show quoted text -> I have a questions I’m hoping someone can answer based on experience…. > I have a 1989 GMC Sierra K1500 4×4 that currently has a 305cid engine. I was > in the right place at the right time and was given a 1994 350cid engine > (140,000km) that came out of a truck identical to mine except newer. Since > the oil pressure on my 305 is getting on the low side (165,000km) I was > planning to rebuild it soon anyway, so instead we are building the 350 to > replace the 305. > The cylinders on the 350 were a couple thousands out of spec so we decided > to bore the block 0.030" oversided and buy new pistons. Before the rebuild > we calculated the compression ratio to be around 8.3 to 8.5:1 (stock). The > high-output versions of the 350 have a ratio of 9.5:1. We decided to boost > the compression ratio by buying the high-output pistons. Now we calculate > the compression ratio to be somewhere between 9.6 and 9.8:1 (estimating the > deck height since the pistons are not installed yet). > Now my question…will I still be able to run regular unleaded fuel > (Canadian) in this engine? I believe the octane rating of our unleaded is 87 > with supreme being 91. I am planning to use my 305’s TBI and associated > electronics since according to my service manual there is no difference > except the EPROM which I may replace after testing. If I’m going to have > trouble with regular unleaded I will install a set of thicker head gaskets > to get the ratio down to around 9.5:1 or a little lower. > Thanks for any advice! > Ken R. > Nova Scotia, Canada
—–= Posted via Newsfeeds.Com, Uncensored Usenet News =—– http://www.newsfeeds.com – The #1 Newsgroup Service in the World! —–== Over 80,000 Newsgroups – 16 Different Servers! =—–
Response:
I have a questions I’m hoping someone can answer based on experience…. I have a 1989 GMC Sierra K1500 4×4 that currently has a 305cid engine. I was in the right place at the right time and was given a 1994 350cid engine (140,000km) that came out of a truck identical to mine except newer. Since the oil pressure on my 305 is getting on the low side (165,000km) I was planning to rebuild it soon anyway, so instead we are building the 350 to replace the 305. The cylinders on the 350 were a couple thousands out of spec so we decided to bore the block 0.030" oversided and buy new pistons. Before the rebuild we calculated the compression ratio to be around 8.3 to 8.5:1 (stock). The high-output versions of the 350 have a ratio of 9.5:1. We decided to boost the compression ratio by buying the high-output pistons. Now we calculate the compression ratio to be somewhere between 9.6 and 9.8:1 (estimating the deck height since the pistons are not installed yet). Now my question…will I still be able to run regular unleaded fuel (Canadian) in this engine? I believe the octane rating of our unleaded is 87 with supreme being 91. I am planning to use my 305’s TBI and associated electronics since according to my service manual there is no difference except the EPROM which I may replace after testing. If I’m going to have trouble with regular unleaded I will install a set of thicker head gaskets to get the ratio down to around 9.5:1 or a little lower. Thanks for any advice! Ken R. Nova Scotia, Canada
