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Tuning With C16

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what afr should i look for when tuning c16 under boost on Regular pump gas i run 11.1 and 14.7 on idle

Usually depends on the car and what is its intended use is. For me, I like to start leaning her out a bit till around I get it to 12.2-12.8 and monitor knock. On c16 you can advance timing pretty well. Add timing till the torque curve doesn't move and retard it a few degrees.

Hope this could help you

A leaner mixture under boost will be quite safe using C16 - it's a pretty good fuel. Depending of course on actual boost pressure, I was aiming for around 12.0-12.2:1. You will also be able to advance the timing a fair way compared to what you could run on pump. C16 isn't totally impervious to knock though so you still need to tread carefully.

Hi everyone

I got a question about C16 ,Q16 and VP import how leaner mixture under boost can I go whit like 35 of boot.

from 1 bar of boost what you recommend to be a good staring point and 2 bar also.

That's an interesting question and it would be nice to go on a little more than extensive work experience to answer it. Could it be that the fuel's technical data can give some guidance here? I'm not expecting anything absolute but just a comparison which would translate to some guidance for apprehension?

Or is my thinking not correct?

First of all be aware that Q16 is oxygenated and as such you will need to add around 5% to your current fuel table in order to maintain the same AFRs you were seeing on the likes of petrol or C16. I've only tuned using VP Import once and found that the results were no better than C16 at the time and given the huge cost difference I elected not to try it again.

You can definitely tune leaner on C16/Q16 than on petrol but there isn't usually much to be had from going leaner than the numbers I suggested earlier. I always like to keep a safety buffer and err on the side of rich.

Andre now this days what would you choose from Vp import of VP c85,i have a customer here that always run vp import on his car on a build 4g63 with 50psi boost and direct port NOS.car was one of the old Bushure racing car back in the days and still to day thee been running vp import fuel.My self personally run and tune most car today on e85 e98 or vp c85 and last vpc16

The market has changed a lot over the last 10 years and it would be hard to choose VP Import (or C16/Q16) these days over E85. Pump E85 is what most people will choose but it is quite variable in its nature. C85 on the other hand is a guaranteed consistency so you can be confident in your tank to tank consistency which is understandably important if you're anywhere near the limit.

If I was starting from scratch I'd be tending towards C85 as it's more cost effective however there are some considerations:

1. You need a greater fuel volume on C85 - Around 35-40% more fuel than Import and this will be a consideration in your fuel system sizing.

2. At very high boost levels I've found E85 fuels to be more prone to resulting in head gasket issues. I've put this down to the fact you're combusting a large volume of incompressible liquid compared to the same boost level on a petroleum based fuel.

Ultimately if the car is already tuned and set up for Import it might be smartest just to leave it be. The extra cost of the fuel probably is insignificant vs changing injectors and fuel pumps etc plus retuning.

That's actually a refreshing deduction with respect to the head gasket problem, I would have missed it clearly on my own. I may have swallowed the blame down to my own inexperience at that level.

I hate to high jack this thread like this, and please correct me if I am out of line by doing this, but on standard EJ257 shortblocks fitted to EJ20 cylinder heads (OEM head gasket, OEM head studs), has anyone encountered head gasket failure when mid frame turbochargers (GT30 stock location, run at 1.2 BAR) are installed as an upgrade? Lambda was on the safe side of rich (11 AFR under full load), and ignition advance was conservative (15 degrees).

Any suggestions? I've been told that it's a common problem and that I should use better head studs and I should be okay.

On any performance Subaru build I would be recommending using a set of aftermarket head studs from the likes of ARP - It's a cheap insurance policy. Years ago I built a drag engine based on a 2.5 bottom end that ran methanol.

We used a 14mm head stud kit combined with gas filled o-rings on that engine with good success and these are quite common in a lot of the high power Subaru engines. That however may be slight overkill for a GT30 sized turbo combination - Just discussing the lengths that you can go to on those engines.

Thanks for the prompt response, much appreciated.

I suppose there's no safe way to explore the structural integrity of engine when you're pushing the horsepower limits past the OEM level. I just didn't really see it coming, especially since I wasn't pushing things.

All the same, I am quite happy to learn about the tolerances engines can have and the strategies that can be employed to not only cope but exercise insurance. Last curious question for you Andre, were you an engine builder before you were an engine calibrator or did you transition with both fields simultaneously? For me the learning curve with engines can overwhelm me at times.


@sardengineering I kind of fell into both roles simultaneously to be honest. When I got involved in the industry back 15 years ago I was driven by two things:

1. I had no money so hence it was difficult to pay others to do the work I wanted done.

2. I had a distinct lack of trust for others to do work to the level I expected it to be done. It turns out this is a very real issue and one of the motivators for us creating HPA :)

As a bit of background I built my first engine at the age of 13 (I think). It was only a 50 cc kart motor but the principles don't change too much.

I learnt a lot from the 10 years or so I was actively developing our 4G63 drag engines. This let me test tolerances and play with many different ideas to help hold these engines together and keep them reliable at 1000 + whp and 10,000 + rpm. I guess looking back, that experience was invaluable to me from both a tuning and engine building perspective - I learnt a huge amount in a short time.