A998 & TF-1 - Harsh 2-3 shift
Wow, thanks for your detailed reply, again!
Ohhhhhh; I gotta think on that.
Ok I think I mighta stumbled on your problem.
Near as I can figure out is that the Whiplash cam was designed to be run in conjunction with long-tubes.But it's really hard to figure out with not knowing the seat to seat duration.
The thing I see is that by tightening up the LSA to 107, they have increased the overlap period drastically, from their typical fast rate cams.This period really only works with long-tubes. The long-tube headers put a "suction" on the back of the exhaust valve,into the chamber,and onto the front of the intake valve, that helps to get the AF charge get moving from the carb towards or into the chamber,before the piston starts moving down on the intake stroke.
With shorties this does not happen at the usual time, and the effect is much reduced.
The result of that is EGR; lots of exhaust remaining in the chamber at low rpm.
Your chamber is not being properly evacuated by the header at low speed, and the intake-charge is not being jerked into the chamber, so the piston has to do all the work. The result is that at low idle, the engine is barely making enough torque to keep itself running, never mind fighting the tranny.And I think that maybe why 24* of idle-timing is required. I'm starting to think you may actually have as good a tune on that engine as can be expected with the parts you are using.
I haven't heard about shorty headers might being a issue with tight LSA before, thanks for bringing it up. It has always been to my impression that tight LSA cams make low vacuum, and need more RPM to stay alive at idle.
Hughes doesn't mention anything about header changes on their website.
This is the camshaft I run;
Hughes Engines
On the flat tapet Whiplash cam though, they do mention vacuum to be in the 9"-11" range;
Hughes Engines
The best advice I can offer is to call Hughes, and see if they can verify my theory. And until then, put post *20 on hold. You may need to either swap the cam out or get some long-tubes. And if you can get them to release the seat to seat specs on that cam,boy!, that would sure help me out.
I emailed Hughes yesterday asking about what idle quality/speed I should be able to get. I will see what they have to say about this first.
Now also,about that cam; it probably has a very early closing intake angle, and that will trap a strong mixture, to the point that even with about 9.3 Scr, the Dcr will be quite high, perhaps too high. Have you been having trouble with detonation? or do you burn top grade fuel?
I spent some time playing with fictional numbers as to the Whiplash specs, but I don't think it would help you much, cuz I just am having a hard time imagining the seat to seat specs of that cam.
I see you are in Norway, so a phone call might get expensive, but you have other options. I feel very strongly, that you should get the info you need straight from the guy that knows.
I am very eager to see how this plays out, cuz until now I was kindof stumped.I have never tuned a combo like yours, so I'll be learning alongside you, and learning is always exciting for me.
Until then, all the best to you.
My calculations gave me 9.64 SCR.
I have not been having issues with detonation, as far as I know (but we haven't been using equipment for listening to knock). I run a fuel that equals your 91 Octane.
I posted my dyno results here;
My 318 dyno results
Based on these results I feel the engine looks healthy, even though Hughes meant I should have made even more power. Being the short duration cam it is, I believe it seems about right from my power figures?
I'm very happy with how the camshaft drives, with the exeption of the idle quality. I wouldn't mind high idle RPM, but I hate that harsh engagement.
The only thing that I believe was out of spec doing the engine build, is that I run quite some lifter preload, about .110"-.120". Hughes recommends .090"-.095" using their 5006 lifters with aluminum heads, so I'm not that far off either. They told me I should be fine running the higher preload.