Compression ratio
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Intermediate
Joined: Jan 2015
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From: Killeen Texas
Compression ratio
Here's the deal. I have a 77 and did a big block swap. Put in a 454 .020 over (thought that was kinda weird while building). Tried the peanut port heads but they were god-awful, big surprise, I know. Ended up getting aluminum heads, ls7 aluminum intake, dewitts & spal, 1.73 roller rockers and some fairly decent comp cam. Long story short chewed up a lifter and lobe so I got a Lunati retro roller with 570 lift. Got a 140 amp alternator and electric water pump while I was at it. I figured since I'm doing the rebuild I should go ahead and bump up compression too. Problem is I'm not quite sure how much I can go. I have a 115cc head chamber, and boring .030 over. By my calculations a dome -30 piston would be around 10.5:1. Would that be good, without detonation, on pump 93 in the middle of the Texas summer heat?
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Need to know piston to deck clearance, head gasket size (bore and thickness), and cam timing to properly calculate dynamic compression.
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Intermediate
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From: Killeen Texas
Haven't actually gotten the pistons yet and don't know the deck height. Taking it to the machine shop this week. Haven't gotten the head gasket either, but seems they're mostly .040. And the cam is lunati 20110120LK.
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If you end up with a true 10.5 compression ratio you'll be more than safe on 93 octane. My 555" was 11.56 before going to turbos and I drove, raced and dyno'd on 93 octane in both Houston and Dallas heat. Never had an issue.
The trick is to keep it cool and get the tune right.
For reference..my pistons are .009" OUT of the hole. I run it real close with a total distance from the head of .028"- to .032" depending on what configuration the motor is in. I think it helps to have tight quench. I'm a little radical on it...but you'd be safe at .040" total.
JIM
EDIT- I just looked at your cam specs....wow that's an awful short duration dude. What RPM range are you trying to achieve? That thing is going to run out of steam early. It's also going to be tough to do with strong compression ratio.
The trick is to keep it cool and get the tune right.
For reference..my pistons are .009" OUT of the hole. I run it real close with a total distance from the head of .028"- to .032" depending on what configuration the motor is in. I think it helps to have tight quench. I'm a little radical on it...but you'd be safe at .040" total.
JIM
EDIT- I just looked at your cam specs....wow that's an awful short duration dude. What RPM range are you trying to achieve? That thing is going to run out of steam early. It's also going to be tough to do with strong compression ratio.
Last edited by 427Hotrod; Apr 2, 2016 at 02:08 AM.
Thread Starter
Intermediate
Joined: Jan 2015
Posts: 45
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From: Killeen Texas
If you end up with a true 10.5 compression ratio you'll be more than safe on 93 octane. My 555" was 11.56 before going to turbos and I drove, raced and dyno'd on 93 octane in both Houston and Dallas heat. Never had an issue.
The trick is to keep it cool and get the tune right.
For reference..my pistons are .009" OUT of the hole. I run it real close with a total distance from the head of .028"- to .032" depending on what configuration the motor is in. I think it helps to have tight quench. I'm a little radical on it...but you'd be safe at .040" total.
JIM
EDIT- I just looked at your cam specs....wow that's an awful short duration dude. What RPM range are you trying to achieve? That thing is going to run out of steam early. It's also going to be tough to do with strong compression ratio.
The trick is to keep it cool and get the tune right.
For reference..my pistons are .009" OUT of the hole. I run it real close with a total distance from the head of .028"- to .032" depending on what configuration the motor is in. I think it helps to have tight quench. I'm a little radical on it...but you'd be safe at .040" total.
JIM
EDIT- I just looked at your cam specs....wow that's an awful short duration dude. What RPM range are you trying to achieve? That thing is going to run out of steam early. It's also going to be tough to do with strong compression ratio.
Last edited by 77vet; Apr 2, 2016 at 11:48 AM.
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Who's heads as well?
I know the Edelbrock like a 107. Chris Straub sold me this one for the Edelbrock heads
.050” 229/235
Lift .590/.559
Centers 103/111
LSA 107
I came out with 9.8:1 compression when it was all done. I wish it was more but really for a street car it's just fine. Tire smoking torque and great freeway manners.
I know the Edelbrock like a 107. Chris Straub sold me this one for the Edelbrock heads
.050” 229/235
Lift .590/.559
Centers 103/111
LSA 107
I came out with 9.8:1 compression when it was all done. I wish it was more but really for a street car it's just fine. Tire smoking torque and great freeway manners.
Thread Starter
Intermediate
Joined: Jan 2015
Posts: 45
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From: Killeen Texas
Who's heads as well?
I know the Edelbrock like a 107. Chris Straub sold me this one for the Edelbrock heads
.050” 229/235
Lift .590/.559
Centers 103/111
LSA 107
I came out with 9.8:1 compression when it was all done. I wish it was more but really for a street car it's just fine. Tire smoking torque and great freeway manners.
I know the Edelbrock like a 107. Chris Straub sold me this one for the Edelbrock heads
.050” 229/235
Lift .590/.559
Centers 103/111
LSA 107
I came out with 9.8:1 compression when it was all done. I wish it was more but really for a street car it's just fine. Tire smoking torque and great freeway manners.
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Don't really plan on running the strip, mostly just stoplight to stoplight. It's only a 2-bolt main so I don't want to try and build it to spin way up, I think that's more for small blocks. The cam operating range is 1600-5600, and since it's a roller, duration can be shorter than a flat tappet with the same effect. The lift with stock 1.7 rockers is .570 and my 1.73s will make it about .580". Should be nice and thumpy, lol. Match that with the stall and I got a fun little toy to zip around town. I also got a cloyes timing cover so it's easy to swap cams without tearing everything apart (other than taking off the intake). Wanted to add some compression to get that extra pop since it's a little more work to change pistons.
Cam selection has a LOT to do with what heads you have. Might be worth investigating them a little closer to determine what they might flow on the intake and exhaust side. You've got an LS-7 intake...not sure what that is. LS-7's were sold over the counter without an intake....so I'm assuming this is a rectangular port GM intake that's either like an L72 high rise 427 style (used on LS-6 crate motors too) or one of the pancake style intakes for Vette's/Chevelle's with LS-6's. Do the heads have rectangular ports...or ovals or the "squoval/roval" type like Edelbrocks? Big heads with a mild cam takes a little work. The heads start to really work about the time the cam signs off. That said..you don't need big heads on a 454 at all....some good ovals will make 600+ HP all day long.
I think peak HP will come in at the low 5000 RPM range..so if that's what you're looking for you'll get it. Two bolt main isn't an issue at this HP level and 6500 RPM wouldn't even begin to worry me as long as I had forged pistons and it was assembled correctly.
JIM
Last edited by 427Hotrod; Apr 2, 2016 at 12:51 PM.
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Thread Starter
Intermediate
Joined: Jan 2015
Posts: 45
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From: Killeen Texas
Yep..it's got good lift considering the duration. Not sure how thumpy it will be with that duration on a 112 LSA. Actually should be pretty darn smooth..but everyone has their own idea of smooth and thumpy.
Cam selection has a LOT to do with what heads you have. Might be worth investigating them a little closer to determine what they might flow on the intake and exhaust side. You've got an LS-7 intake...not sure what that is. LS-7's were sold over the counter without an intake....so I'm assuming this is a rectangular port GM intake that's either like an L72 high rise 427 style (used on LS-6 crate motors too) or one of the pancake style intakes for Vette's/Chevelle's with LS-6's. Do the heads have rectangular ports...or ovals or the "squoval/roval" type like Edelbrocks? Big heads with a mild cam takes a little work. The heads start to really work about the time the cam signs off. That said..you don't need big heads on a 454 at all....some good ovals will make 600+ HP all day long.
I think peak HP will come in at the low 5000 RPM range..so if that's what you're looking for you'll get it. Two bolt main isn't an issue at this HP level and 6500 RPM wouldn't even begin to worry me as long as I had forged pistons and it was assembled correctly.
JIM
Cam selection has a LOT to do with what heads you have. Might be worth investigating them a little closer to determine what they might flow on the intake and exhaust side. You've got an LS-7 intake...not sure what that is. LS-7's were sold over the counter without an intake....so I'm assuming this is a rectangular port GM intake that's either like an L72 high rise 427 style (used on LS-6 crate motors too) or one of the pancake style intakes for Vette's/Chevelle's with LS-6's. Do the heads have rectangular ports...or ovals or the "squoval/roval" type like Edelbrocks? Big heads with a mild cam takes a little work. The heads start to really work about the time the cam signs off. That said..you don't need big heads on a 454 at all....some good ovals will make 600+ HP all day long.
I think peak HP will come in at the low 5000 RPM range..so if that's what you're looking for you'll get it. Two bolt main isn't an issue at this HP level and 6500 RPM wouldn't even begin to worry me as long as I had forged pistons and it was assembled correctly.
JIM
Wasn't planning on going forged since I'm not running nos, I think a good set of domed hyper-e's will hold up just fine. Just don't want to overdue compression.
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From: Killeen Texas
You may be right, but it's cheaper to work with what I've got. I'm already much happier with them over the previous peanut ports. I may end up there in the future, but my next plans after this rebuild are a 700r4 and 3.73s. With the low first gear of the 700 and a good rear end, I think that cam will bring it to life. No, it may not have a great top end, but definitely takes off from a red light and still able to drive on the highway daily.
Last edited by 77vet; Apr 2, 2016 at 01:49 PM.
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Those aren't GM heads. Those are some of the imports sold under lots of labels. Some of them work OK if you REALLY ck them over as far as valve guide clearances and valvejob.
Hypers will do OK if you're only planning on 5500 rpm or so and don't get any detonation. Watch your tune.
JIM
Hypers will do OK if you're only planning on 5500 rpm or so and don't get any detonation. Watch your tune.
JIM
Thread Starter
Intermediate
Joined: Jan 2015
Posts: 45
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From: Killeen Texas
Those aren't GM heads. Those are some of the imports sold under lots of labels. Some of them work OK if you REALLY ck them over as far as valve guide clearances and valvejob.
Hypers will do OK if you're only planning on 5500 rpm or so and don't get any detonation. Watch your tune.
JIM
Hypers will do OK if you're only planning on 5500 rpm or so and don't get any detonation. Watch your tune.
JIM
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
I would get your machinist to go through the heads completely, meaning taking apart and inspecting everything. You might need different springs than the ones on there right now. $900 for a complete set of BBC heads has me worried. 