Why mod R33 is slower than stock R33 – data logs

[TomR33]

I have compared data logs from my slightly modified R33 GTST 95 model Skyline to almost stock R33 GTST 95 model. The almost stock car is faster and only has a HKS pod filter, high flow cat and higher boost (about 12 PSI). I have full 3” exhaust (dump pipe with separate wastegate pipe), high flow cat, ARC front mount intercooler, HKS pod filter, higher boost (about 12 PSI). Both use stock ECUs without any piggy backs. My car made 200rwkw on the dyno but is still slower.

Have a look at the timing graph, my timing drops to 5 deg where the timing on the stock car is still in the 19s. That area is not in the knock map so I believe its due to the higher air flow 4.8 V compare to the stock car 4.5 V. What do you all think?

http://home.iprimus.com.au/tkolo/datalog.htm

[riggaP]

I think that your FMIC could be the reason. It would be more laggy as the turbo has to work harder to fill the larger coola. A piggy back band aid might help your cause.

[Sydneykid]

Hi TomR33, it looks to me as though your car is hitting the boost limiter, the AFM is close to max voltage and the ECU is adding fuel and taking timing out of it to protect the engine.

The standard (er) car has none of these issues, so is running on the full power maps on the ECU.

You need some form of a boost cut defeater and a voltage clamp on the AFM. There are a number of brands available for around $200 each.

This is a common problem with R33's, you get increased performance from each mod you add. Up until you hit the boost and voltage limits, then the ECU does what is programmed to do and cuts the power.

If you want to do it properly, I would strongly suggest you look at a Power FC. By the time you add up the costs of SAFC, ITC, BCD, TSLD etc its works out more than a Power FC and will never be as good.

Hope that helps

[TomR33]

Thanks for the info Sydneykid. I thought it would be something like that. I was expecting a boost cut to be something violent like a rev cut or speed cut but maybe the ECU just starts with taking the timing out. The biggest drop (only 5 deg) is at 4800 rpm where AFM is at 4.8v. After that the air flow goes up to 5.0v and the timing goes up to 23 deg at 6600 rpm. So that tells me that there must be a different air flow limit for different RPM i.e. 5.0v for 6600rpm - OK, 4.8v for 4800rpm - too much.

In theory if I lower my boost (air flow) I should be able to at least match the performance of the other car, right?

[predator]

I think that is probably what you'll find.. You should still be able to run 10pound and get a comfortable 180-190rwkw. In many 33, including my own, generally people find the sweet spot is not the possible 14psi, but around 10 or 11psi

[rev210]

perhaps another issue you have is with engine response.

To make back the engine response you are missing you can do things like wrap the dump pipe in thermal tape, fit a lighter flywheel and redesign the intercooler pipe setup to minimise length and volume.