Bliue dm Posted July 29, 2020 Share Posted July 29, 2020 Ok. So i just recently purchased a 97 688s with a e7 400. Semi electric. Its only making 25psi boost. I know our etech 400 is making around 32psi. Is my boost preasure off our is 400hp achieved thru timing? Or is my boost preasure low? Quote Link to comment https://www.bigmacktrucks.com/topic/63511-1997-mack-e7-400/ Share on other sites More sharing options...
Bliue dm Posted July 29, 2020 Author Share Posted July 29, 2020 I would like to also know the difference between it and other e7 400. There is so much on this topic like. I hear some of these engines have two piece pistons... Some people say the compression ratio are different but when you look at a mack chart you see thats not true? Quote Link to comment https://www.bigmacktrucks.com/topic/63511-1997-mack-e7-400/#findComment-457096 Share on other sites More sharing options...
brettj3876 Posted August 4, 2020 Share Posted August 4, 2020 On 7/29/2020 at 7:13 PM, Bliue dm said: I would like to also know the difference between it and other e7 400. There is so much on this topic like. I hear some of these engines have two piece pistons... Some people say the compression ratio are different but when you look at a mack chart you see thats not true? Your boost sounds a bit low. Think it should be 28 at the min to 32. Don't have the book in front of me now. They have 2 piece piston. Steel top/alum skirt. Give mack the ser# to find out what comp pistons it has. They were all over the place in diff years. For example the 93's 250-400 all had 16.9:1 (conflicting info around) some literature says 375 and up 15.3 and below that 16.5 but mack had changes over the yrs. One book said our 93 was 16 5 and another 16.9. It ended up being 16.9:1 (591 tops) I doubt it's 16.9 could be 16.5 15.7 or 15.3 Quote Link to comment https://www.bigmacktrucks.com/topic/63511-1997-mack-e7-400/#findComment-457607 Share on other sites More sharing options...
JoeH Posted August 4, 2020 Share Posted August 4, 2020 My 95 e7-350 (all mechanical) tops out at about 25 psi boost. It has trouble getting out of it's own way, but it gets where it's supposed to go. Will make 1200+ degrees EGT, though I try not to push that number. I just assume it's working as it should.... Quote Link to comment https://www.bigmacktrucks.com/topic/63511-1997-mack-e7-400/#findComment-457645 Share on other sites More sharing options...
brettj3876 Posted August 4, 2020 Share Posted August 4, 2020 2 hours ago, JoeH said: My 95 e7-350 (all mechanical) tops out at about 25 psi boost. It has trouble getting out of it's own way, but it gets where it's supposed to go. Will make 1200+ degrees EGT, though I try not to push that number. I just assume it's working as it should.... Post turbo probe? I would keep try to keep it under 1050. Our says 1025 max and 99 says 1100 max. 1200 won't hurt it for short bursts but deff don't pull a couple mile grade like that Quote Link to comment https://www.bigmacktrucks.com/topic/63511-1997-mack-e7-400/#findComment-457654 Share on other sites More sharing options...
Bliue dm Posted August 6, 2020 Author Share Posted August 6, 2020 On 8/4/2020 at 12:51 AM, brettj3876 said: Your boost sounds a bit low. Think it should be 28 at the min to 32. Don't have the book in front of me now. They have 2 piece piston. Steel top/alum skirt. Give mack the ser# to find out what comp pistons it has. They were all over the place in diff years. For example the 93's 250-400 all had 16.9:1 (conflicting info around) some literature says 375 and up 15.3 and below that 16.5 but mack had changes over the yrs. One book said our 93 was 16 5 and another 16.9. It ended up being 16.9:1 (591 tops) I doubt it's 16.9 could be 16.5 15.7 or 15.3 I will get serial number 4 you... its suppose to be a 400. Sounds like it can use a valve adjustment. Quote Link to comment https://www.bigmacktrucks.com/topic/63511-1997-mack-e7-400/#findComment-457828 Share on other sites More sharing options...
Bliue dm Posted September 2, 2020 Author Share Posted September 2, 2020 9d Quote Link to comment https://www.bigmacktrucks.com/topic/63511-1997-mack-e7-400/#findComment-459976 Share on other sites More sharing options...
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