S4 Heads To S3 Block
03-10-2018, 06:36 AM
#1
Three Wheelin'
Thread Starter
S4 Heads To S3 Block
I've tried searching but haven't found much. Do they fit? Would like the larger valves and slightly higher compression but will put my S3 cams in the S4 heads.
03-10-2018, 12:06 PM
#2
Rennlist Member
I have a feeling there is a reason why the S4 heads do not fit to the S3 and no idea what exactly the issue might be but I take it you understand that you have to modify the S3 cams to fit the S4 heads, specifically the 5/8 exhaust cam has to have a thrust collar fitted..
03-10-2018, 01:33 PM
#3
Rainman
Rennlist Member
Rennlist Member
S4 heads ~42cc chamber
S3 heads ~56cc chamber
+
S4 pistons ~25cc dish
S3 pistons ~7cc dish
=
S4 heads on S3 pistons = ~12:1 compression
S3 heads on S4 pistons = ~8:1 compression
Probably worth looking into running those long-duration S3 cams somewhat retarded to bleed cylinder pressure at lower RPM if you're running pump gas.
The Real issue of fitment is that S4 has larger intake valves than S3 (37mm vs 35) and the notches in the S3 pistons will need to be enlarged to clear.
S3 heads ~56cc chamber
+
S4 pistons ~25cc dish
S3 pistons ~7cc dish
=
S4 heads on S3 pistons = ~12:1 compression
S3 heads on S4 pistons = ~8:1 compression
Probably worth looking into running those long-duration S3 cams somewhat retarded to bleed cylinder pressure at lower RPM if you're running pump gas.
The Real issue of fitment is that S4 has larger intake valves than S3 (37mm vs 35) and the notches in the S3 pistons will need to be enlarged to clear.
03-11-2018, 10:46 PM
#4
It’s tight but there is no clearance issue for the s4 valves. I gave it a bit of clearance at each intake valve picked as I recall, but it’s not as close as you think.
03-12-2018, 09:22 AM
#6
Rennlist Member
Search function seems limited
https://rennlist.com/forums/928-foru...-engine-3.html
I grabbed the above thread from my saved threads. It has some discussion on the topic. There are other threads with such discussions.
Its probably already been discussed here but it seems the search function is not working well. Nothing came up when I searched titles only with S3 and S4 in them, but I have a bunch of saved ones with just that.
I grabbed the above thread from my saved threads. It has some discussion on the topic. There are other threads with such discussions.
Its probably already been discussed here but it seems the search function is not working well. Nothing came up when I searched titles only with S3 and S4 in them, but I have a bunch of saved ones with just that.
Last edited by hernanca; 03-15-2018 at 10:15 PM. Reason: spellin'
03-12-2018, 02:25 PM
#7
Trending Topics
03-12-2018, 06:54 PM
#8
Three Wheelin'
Thread Starter
Ok. Thanks. Mine is of course the Australian version which used slightly lower compression again compared to the US motor. I might need to find out exactly what it is and see if fitting the S4 heads yields a usable compression ratio given no knock sensors on these engines.
03-12-2018, 06:57 PM
#9
Rennlist Member
Another old (saved) thread summing up some of the differences:
https://rennlist.com/forums/928-foru...32v-heads.html
https://rennlist.com/forums/928-foru...32v-heads.html
03-12-2018, 10:03 PM
#10
Ok. Thanks. Mine is of course the Australian version which used slightly lower compression again compared to the US motor. I might need to find out exactly what it is and see if fitting the S4 heads yields a usable compression ratio given no knock sensors on these engines.
03-13-2018, 12:16 AM
#11
Three Wheelin'
Thread Starter
Is it possible to use a thicker head gasket to bring the ratio down a bit? If I can get the compression down to 11:1 I think that would be quite streetable on 98RON. I'm wondering what sort of HP with MSDS Headers, X-Pipe, FPR and Porkens chipset programmed to suit the motor. I'd think one would have to run cold plugs as well.
Last edited by DeWolf; 03-13-2018 at 06:51 AM.
03-13-2018, 10:18 AM
#12
Rennlist Member
Which custom intake do you plan on using since none are currently available? Do you plan on making one yourself?
03-13-2018, 10:58 AM
#13
03-14-2018, 12:56 AM
#14
Rennlist Member
Old thread links: S3 cams in S4 motor, S3 vs S4 motor differences.
A few more from the archives:
Sept. 2005, various cam comparisons:
https://rennlist.com/forums/928-foru...ml#post2463132
May 2010, S3 vs S4 motor differences:
https://rennlist.com/forums/928-foru...-s4-motor.html
January 2009, 85/86 cams in S4, mods:
https://rennlist.com/forums/928-foru...ml#post6200435
Sept. 2005, various cam comparisons:
https://rennlist.com/forums/928-foru...ml#post2463132
May 2010, S3 vs S4 motor differences:
https://rennlist.com/forums/928-foru...-s4-motor.html
January 2009, 85/86 cams in S4, mods:
https://rennlist.com/forums/928-foru...ml#post6200435
Last edited by hernanca; 03-15-2018 at 10:20 PM. Reason: Added more links.