427 Re Rebuild
Thread Starter
Racer
Joined: Apr 2013
Posts: 302
Likes: 16
427 Re Rebuild
I have a question with compression ratio.
Had the 427 rebuilt the 1st time.... had a issue with oil being sucked into the intake ports of the heads. The intake wasn't sealing correctly and the engine was burning oil. The rebuilder is going through the engine again checking everything out. The first rebuild the compression ratio was at 9.3 to 1. Should I have the compression ratio increased closer to 10 to 1. Are there any advantages increasing the ratio or should I leave it at 9.3 to 1.
I know a higher octane fuel will be needed..
But would the engine gain more power or is it a wash if the timing needs retarded to avoid pinging.
Appreciate your experiences.
Had the 427 rebuilt the 1st time.... had a issue with oil being sucked into the intake ports of the heads. The intake wasn't sealing correctly and the engine was burning oil. The rebuilder is going through the engine again checking everything out. The first rebuild the compression ratio was at 9.3 to 1. Should I have the compression ratio increased closer to 10 to 1. Are there any advantages increasing the ratio or should I leave it at 9.3 to 1.
I know a higher octane fuel will be needed..
But would the engine gain more power or is it a wash if the timing needs retarded to avoid pinging.
Appreciate your experiences.
Race Director
Joined: Nov 2006
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From: Sunshine Coast, Queensland, Australia
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Compression makes power.
nuff said.
nuff said.
Dr. Detroit
Joined: Mar 2012
Posts: 10,095
Likes: 4,025
From: New Braunfels Texas
.7 of a point of compression at this level is worth about ten horsepower. Lot of money for ten horsepower.
Now there are many other factors as to why you should run more compression...but the big one is the camshaft. Do you have a lot of overlap? Measured compression helps deal with this for the sake of drivability and tuning.
I would leave the compression alone and have the heads done up like a previous poster said......bad *** 5 angle valve job, backcut stainless valves.....and some blending. The way Mark/Vortecpro sets them up......
Is this an oval port closed chamber engine? I had a 427/400 that had a mild dome for 10.3 to 1 and it did not like fuel here in Texas with my curve in it.......closed chambers are that way.
Jebby
Now there are many other factors as to why you should run more compression...but the big one is the camshaft. Do you have a lot of overlap? Measured compression helps deal with this for the sake of drivability and tuning.
I would leave the compression alone and have the heads done up like a previous poster said......bad *** 5 angle valve job, backcut stainless valves.....and some blending. The way Mark/Vortecpro sets them up......
Is this an oval port closed chamber engine? I had a 427/400 that had a mild dome for 10.3 to 1 and it did not like fuel here in Texas with my curve in it.......closed chambers are that way.
Jebby
Last edited by Jebbysan; Aug 25, 2020 at 07:40 AM.
Thread Starter
Racer
Joined: Apr 2013
Posts: 302
Likes: 16
.7 of a point of compression at this level is worth about ten horsepower. Lot of money for ten horsepower.
Now there are many other factors as to why you should run more compression...but the big one is the camshaft. Do you have a lot of overlap? Measured compression helps deal with this for the sake of drivability and tuning.
I would leave the compression alone and have the heads done up like a previous poster said......bad *** 5 angle valve job, backcut stainless valves.....and some blending. The way Mark/Vortecpro sets them up......
Is this an oval port closed chamber engine? I had a 427/400 that had a mild dome for 10.3 to 1 and it did not like fuel here in Texas with my curve in it.......closed chambers are that way.
Jebby
Now there are many other factors as to why you should run more compression...but the big one is the camshaft. Do you have a lot of overlap? Measured compression helps deal with this for the sake of drivability and tuning.
I would leave the compression alone and have the heads done up like a previous poster said......bad *** 5 angle valve job, backcut stainless valves.....and some blending. The way Mark/Vortecpro sets them up......
Is this an oval port closed chamber engine? I had a 427/400 that had a mild dome for 10.3 to 1 and it did not like fuel here in Texas with my curve in it.......closed chambers are that way.
Jebby
in / ex lift is .555 219/227 110+4 LC Hyd roller
Last edited by Z06CE; Aug 25, 2020 at 08:43 AM.
Dr. Detroit
Joined: Mar 2012
Posts: 10,095
Likes: 4,025
From: New Braunfels Texas
Thought maybe you were thinking of changing pistons, which is not worth it....
Jebby
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Old Pro Solo Guy
Joined: Dec 2017
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From: Marlton NJ
Very low duration cam + old closed chamber iron heads...I would leave the compression where it is.
It is the Dynamic Compression Ratio that really matters. which takes into account the cam duration. or IVC pt.
There are calculators online at Wallace Racing and others.
Stay under 7.8-8.0 DCR for street gas on Iron heads or it'll ping bad.
1 point of increase isn't worth the effort for power anyway....
It is the Dynamic Compression Ratio that really matters. which takes into account the cam duration. or IVC pt.
There are calculators online at Wallace Racing and others.
Stay under 7.8-8.0 DCR for street gas on Iron heads or it'll ping bad.
1 point of increase isn't worth the effort for power anyway....