Hot Rod Forum banner
1 - 3 of 3 Posts

·
Registered
Joined
·
32 Posts
Discussion Starter · #1 ·
A nasty valve cover gasket leak has prompted me to pull the covers off to reseal, while I'm in there I'm considering playing with cam timings again to see how it responds/reacts:



The engine is a BMW M62B44 4.4L (268ci) DOHC V8, 9.6:1 static compression ratio. Jaguar Eaton M112 on adapters, making 8-10psi.
Universal standalone EFI controller running paired cylinder semi-batch injection and waste spark ignition.

It is using factory camshafts for the cylinder heads (BMW M60B40 4.0L), they are a reverse split pattern. 249 duration intake and 241 duration exhaust (.1mm/.004"). In factory trim the cam timings land 110 ICL 108LSA with 29° of overlap. 8.23:1 DCR at sea level before boost.

Utilizing the OE adjustable cam gears I'veI previously experimented with 112 ICL and 110 LSA, now It is currently set up for a 104 ICL and 108 LSA. 8.52:1 DCR and I measured roughly 155-163psi cranking per cyl. The cam timing advancement was a step in the right direction by the reaction of it's street manners.

I've got a crazy idea to try. Experiment with a 100 ICL and 100 LSA, which would increase overlap from 29° to 45° and bump DCR up to 8.7:1. The overlap is still within the realm of sensible computer grind cam specs despite that 100 ICL / 100 LSA sounds nuts in conversation.

What are your thoughts? Small duration, tight LSA reverse split pattern on a small displacement V8?

Video of cruising around the town (with the 104 ICL / 108 LSA):

 

·
More for Less Racer
Joined
·
20,942 Posts
Only thing I can see is that you may be getting too far into the point that it just blows too much fresh charge out the exhaust since you are delaying exhaust closing point while opening the intake earlier.....it may just be a bridge too far. might just get louder and less fuel efficient with no real power gain.
Probably the only way to find out is cut and try.

The 100° ICL doesn't sound nuts to me, it closes the intake really early and this traps a lot of fresh charge at lower rpm but that 100° LSA is a real outlier. Only thing I've seen remotely similar is restricted intake dirt oval short track cams....stock 2 barrel class stuff where the carb is really small so they use a tight LSA to get the most out of the exhaust draw pulse on overlap.
You don't seem to be intake restricted.
As a general rule, boosted street engines generally prefer wider LSA so you aren't just flushing fresh boosted intake charge out the exhaust pipe during overlap.

Maybe try the 100° ICL but with 108°and 104° LSa first before going whole hog on small LSA??

Very neat ride, by the way. Sounds better than this domestic boy thought it would. (y) Reminiscent of old Indy car or WWI biplane almost
 

·
Registered
Joined
·
32 Posts
Discussion Starter · #3 ·
The first experiment: Went straight for the kill with the 100° ICL & 100° LSA. Need to re-tune the VE table, had to remove 15% fuel to get to this point. I expected the cam changes to reduce volumetric efficiency. Also dropped idle ign timing from 18° to 12° for increased effect.


If tuning proves problematic, or I'm sacrificing street mannors and response I'll back it up to 100° ICL / 104° LSA, or 104° ICL / 104 LSA° Worse case, I know that my previous 104° ICL / 108° LSA was a sweet spot and put it back that way.
 
1 - 3 of 3 Posts
Top