Sale ends todayGet 30% off any course (excluding packages)

Ends in --- --- ---

Boost run away hondata s300

General Tuning Discussion

Forum Posts



Tech Articles

Discuss all things tuning in this section. News, products, problems and results. 

= Resolved threads


Hey there, I'm tuning my turbo Honda on s300 on wastegate pressure and I'm having a problem with boost rising higher than I want.

Setup is a mac 3 port solenoid, Garrett t3 turbo .63ar, Tial 38mm MV-s with 5.8psi red spring, pump gas 93oct. I'll attach two data logs showing what I'm dealing with.

Attached Files

Did some reading on older threads and if timing is too retarted that could be my boost issue? I’m going to try adding a couple more degrees and see what happens.


This is common on Hondas because the engines flow really well, and the design of the exhaust manifolds often doesn't give the wastegate good priority flow, so too much energy still gets to the turbo.

Can you show us some pictures of your exhaust manifold, wastegate, dump pipe?

Here you go. Tial mvs 38mm 2.5-3in downpipe and mid pipe. No muffler or resonator. Mini ram horn. The wastegate is really crammed back there but it’s pretty decent placement.

Attached Files

A single 38 on a B series with Vtec head with similar wastegate priority to what's pictured will typically make 15-20 psi if you rev it out to see how far it creeps.

What boost level are you hoping for?

This is a H22a. Well, a lot less than 15-20psi lol. I’m honestly scared to go past 12ish since this is a stock unopened engine and the H series ringlands don’t like boost. I had a goal of 350whp on ethanol and 10-12psi.

Ah yea, haven't seen an H in a while. :)

Please forgive me if you already know this. I'm hoping it may help you or someone else finding this thread some day as general boost creep info. When sizing a wastegate, it's about how much energy you need to get rid of rather than how much power you're going to make. I find some people say "I only want to make 300-400 HP, so I only got a 38mm gate", indicating they think big wastegates are for running more power or more boost, when the reality is the lower you want to run the boost, the bigger the wastegate needs to be to slow the turbo down more and keep boost under control.

An extreme example would be lets say you want to run 50 psi on that turbo. You might not need a wastegate at all, or perhaps a 38mm that barely needs to open, because that turbo might barely be able to make that much boost even if the wastegate never opens. Then as you want less boost than the turbos max potential, you need to slow the turbo down, by using the wastegate to divert more exhaust flow away from the turbine.

A 38mm gate may be perfect for that engine if you wanted to run 30 psi boost, but when you want to run really low boost levels, a bigger gate with bigger piping that can waste more exhaust energy is generally needed.

44mm with 2" tubing in and out would be my thought for what you're trying to do, and still might creep a little at very low boost levels. Since your setup is already built, you might as well carefully rev it a bit further and see what happens. Having a boost safety cut in place and watching boost carefully, you can rev a bit higher to see if boost plateaus at a level you can accept or not.

Just be careful because boost creep by its nature indicates boost is not under control. If the gate is already at max flow, putting more load on the engine by being in a higher gear, going up hill, having more weight in the car, or getting better ambient conditions i.e. cooler temperature, lower baro pressure can make the boost creep higher. For example it may only creep to 8 psi on a warm day, then 15 on a cold day. Or only 6 psi in second gear, but 12 in 4th gear. So a single test likely won't give you a full scope of what will happen as conditions vary.

I know some of this may not sound like ideal news, but I hope it helps!

Solid info and thanks for the response! Yeah I bought this kit a while ago when I didn’t know as much so I just thought this gate should work with my 500whp goal not thinking about how it would work with lower boost levels

Good news! I was swapping to the lightest WG spring and noticed the fitting to the bottom of the gate was not machined down far enough and was leaking. It’s a chilly night and finally got it to rev all the way out in vtec to 7200rpm and stay at 8psi. Haven’t tried 4th gear yet and the tune is far from dialed in but now I can ask the boss man about putting the car on the dyno.

Once I play with the timing on the dyno I’ll post up the final results, some graphs and resolve the thread.

Attached Files

Finally got the car on a dyno and without boost control and just on wastegate(4psi) it made 365/267 at 14psi with 20° tapering to 12° timing. The dyno is wrong and I revved out to 7600rpm.

At 7200rpm I see about 10psi from 6800 to redline and adding increments of 200rpm equals an extra ~2psi.

I may look into switching to a 44mm gate in the future but on the track I won’t have traction issues so it’s fine for now. I’m tempted to use some boost control to try and pick up the back end but this is still a 100% stock h22 euro r. It’s probably best to wait until I have another short block ready to go before turning it up more. Car is super fun!

Attached Files

That sounds like great progress. Just be careful since boost creep is not consistent. If air gets any more dense, or load is any higher than on the dyno, it will likely creep more. Set ignition timing and safety measures accordingly so the ECU responds as you'd like it to if boost goes any higher.

Will do! Here’s the VTEC ignition map. I have it built out to 20psi and after 12psi I’m pulling out 1° per psi. Boost cut is set to 15psi and I turned the rev limiter down to 7500rpm. I’m also trying to keep it around 50% ethanol

Attached Files

We usually reply within 12hrs (often sooner)

Need Help?

Need help choosing a course?

Experiencing website difficulties?

Or need to contact us for any other reason?