E85 tuning - how IGN timing affects boost

[skyline_stu]

I did another SR this week and besides the extra fuel I hardly changed the timing and it still made really good power (310rwkw+ on Mainline dyno). It didn't make any more if I added timing so I left it at that. He did a track day yesterday and all went well.

About the only problem was that it was tending to get hot. Yet when it was on 98 it ran nice and cool. Which is very confusing given that usually going to E85 has the opposite effect!

PL

Pete, another relevant tuning variable comes to mind as well. You should have tried retarding the exhaust cam a degree or 2 . I've seen more strange thing happen when the volume of combustion gases increases. Said engine (a 36psi, 500+wrhp CA18) with 1.5' retard on the exhaust cam reduced EGT's by about 40'C, dropped water temp[which tended to increase slowly over several minutes] by a consistent 5'C and picked up 20hp everywhere. Finding the sweet spot takes time. Spool up time didn't change as I expected.

This engine was using ET110 fuel at the time. I deduced [once again after a bit of testing] that the exhaust valve was opening a bit too early, allowing the increased cylinder pressure to be shed into the cooling system through the exhaust port.

I've experienced many times that a ported head will often change cam timing in ways that require optimizing - sometimes differently than expected. Another combo that comes to mind was a RB20 R32 Auto. We did a port 'n polish with a very different valve and seat job that reduced power by a lot - tuning just wouldn't recover the lost power. Boost response became lazy and it got hot. Re-jigging the cam timing turned that one into a tyre frying monster. It still had the stock turbo [and extensivly ported manifolds]. I still remember my GF in the back seat exclaiming 'do THAT again!!' after it baked the tyres right through 2nd gear on the road test. That car ran a low 14psi. 18psi changed the whole shebang again.. The owner was grinning like a cheshire cat by the end of the tuning session.

Modified engines are indeed a brain drain at times. Unless you try experimenting you'll never know the result.

Terry's WLDGTR used to run completly different tunes and cam timing on E85[30psi, 810hp] and ELF turbo max [for 55psi]. That beast made 1000+hp at all 4 wheels. Frightening to ride in with over 1000hp. That's the only time I've been scared stupid in a car. It would jump across 3 lanes as it came into boost - only because in a 500rpm window it gained 600hp.

Stu

[PL]

Thanks Stu,

That makes good sense.

We're gonna have to do some playing with cams timing. Partly because he took it to the track and isn't terribly happy with the torque spread - it's turned into a bit of a monster that's a bit flat in the midrange and pulls so hard up top that it wants to go off the end of the tacho all the time. So I suggested he advance the inlet cam to try and bring the torque down further.

He's also upgraded the turbo from stocky TD06SL2-20G with the 11 blade exhaust wheel to the 9 blade exhaust wheel and he's also changed from the cast comp wheel to the billet one. He's blaming the peakiness on the 9 blade exhaust wheel but I reckon his cam timing might need some closer inspection.

To top all of this off it actually lunched itself last track day. Jury is still out but inlet cam gear has turned on the nose of the cam and ALL valves have hit pistons. WTF? Running 9:1 pistons with BC 264 cams. So investigation is underway. Current theory is that it threw a rocker which then fouled the cam causing inlet cam gear to turn on the nose of the cam (no VCT). Doesn't explain why exhaust valves also hit pistons though! It's not like it's running monster cams or 11:1 pistons or anything.

It's all a bit sad cos he's a smart operator and generally sets everything up perfectly.

PL