So in talking to a good VW friend (who runs a turbo on his 8V 2L dub) over the weekend about my upcoming turbo conversion, mere weeks away, he brought up a point I didn't have a perfect response to. He asked why do a $1500 head that is ported and run 20psi? Just turn your boost up to 23-25psi, as long as it isn't leaning out too much, and you should get the same whp with a stock head and have that $1500 in your pocketbook.

I explained the whole thing about MINI's being weak in the head dept, and people realising 20-30whp depending on mods by doing a worked head. His response was, yeah sure you can do that if you are not able to simply turn the boost up. Those folks are stuck with whatever boost the SC is willing to give them. With a manual boost controller, you can just turn it up! Just like you would if you were running 100-1004 octane and you wanted to run 30psi!

I had no good response. I am hoping the experts can help me out here. Or maybe help save me some coin??

hypothesis:
If you run a FI car with a worked head at 20psi and see 300whp, how is that different than running a car with a stock head at say 22-24psi to get the same whp? Bearing in mind you are monitoring a wideband during DD, and are able to tune the boost with a testpipe on the car(eliminates cat effect), on a dyno to keep the AFR <12.

This hypothesis assumes 91 octane on a DD with fully forged internals and a stock camshaft.

Any takers?

 

As long as the car can run fine at the higher boost, I'm behind you the whole way.

Course, do the headwork + the higher boost.....

 

so why not the headwork annnd higherboost? eh eh?

 

Higher boost puts more stress on the motor. Even if it's within safe operating limits, the overall lifespan might be shortened. It's like adding a good intake, exhaust, etc...you will loose boost but gain hp...a win-win situation.

 

I think the answer lies in the inefficiency of the s/c once it gets to a certain output. The s/c has a limit and once past it, the returns diminish quickly. Doc Ob or someone in the technical realm will likely give a more thorough explanation.

 

Plan on putting a new set of pistons in if you plan on running the boost up to 24-25psi. I wouldnt suggest more than 20psi on stock pistons.

What turbo are you planning on running? With the stock head and intake manifold you will have flow problems. Above 20psi with the gt2871r I didn't see the same hp increase per psi. However I have managed to get 32psi out of the 2871r.

Also I wouldn't suggest going above 20psi on 91. I run 20psi on 93 oct on the east coast.

 

Remember we are talking about a turbo only system, not twin charged. The limits of the SC are the prime motivating factor in removing it completely.

I understand the stress issue. But the real source of stress IMHO would be concerns of running lean and detonation. If that can be avoided at 22-24psi and still get the power you would see from a head worked car at say 18-20psi what's the difference? In additiion the pistons are going to be upgraded and the stock rods and crankshaft are forged already....

 

Thanks Ryan. Pistons are part of the plan. What kind of AFR's were you seeing on 93 and 25psi? I am planning on running the 2871r not the 30. That sucker is just too much like a ski slope when the boost hits. I am hoping the 28 will be a bit more driveable....

 

Well in that case you will prob see detonation at 22-24psi. That is with the factory ecu. However if you were able to control the ignition advance that could be avoided. But if you are using a higher octane and the CP Pistons you should be able to run up to 32psi without problems.

If I were you I would look into a intake manifold with longer runners. The factory runners are way too short for the factory rev limit. Longer runners will move the power into a more usable band.

And if you build the head with Ferrera valvetrain or supertech pieces you can rev the car to 8k with a reflashed ecu (or close to 9k with an aftermarket) and that will be where the car will really shine.

 

Ryan-
I am doing the FBR intake manifold, exhaust mani and head as well as air to water IC and their pistons. Damn limiting factor here in AZ is the 91 crap we get. I can get 100 here in Tucson, but with a move to Prescott this summer I don't think I will be able to get it easily. Did you ever measure your AFRs at 25psi and 91 octane or 93 octane?

I am not doing the valvetrain or fuel system now as it already a pricey project, as you know! I will be running the SAFC with the setup if that alters you opinion on the detonation issue at all.

 

Beware that when replacing the factory pistons with after market ones, the efficiency of the knock detection system in the factory ecu will be diminished greatly due to the different resonance frequency of the non standard pistons. Bottom line, don't count on knock detection and retard with after market pistons. My experience, as well as those of other professional engine builders has been that there are no better pistons for the Mini than those provided by the manufacturer. I know this is not the case with other vehicles but it is with the Mini.

 

Great info to have, and another reason we will be establishing some limits for boost settings on the dyno. Not a perfect solution, but if we keep boost low enough to keep AFR's under we should be okay. I would prefer 11.5, but we'll see what we get. The ultimate mad POWA isn't my goal. I think any FWD car with over 250whp is gonna be crazy fast anyway!!

 

The MINI pistons are the best pistons for the MINI engine?????? Maybe if you are sticking with the m45 blower. The factory ringlands dont like the increased cylinder pressures from nitrous or higher boost pressures from turbos.

Better in the knock detection yes. Better in durability no.

 

You should really look into converting the fuel system to a return setup with an adjustable FPR. Its not too expensive.

If you plan on running 550cc injectors you will not be able to cut the fuel back enough with an AFC. The car won't idle if you remove the charger. The only injector size I am aware of that work at the stock fuel pressures are the factory injectors.

And when you start cutting the fuel back on the AFC you will be increasing the ignition advance also. Bad for detonation issues.

As far as AFR I have not ran out of fuel on the stock fuel pump even up to 32 psi.

I believe you have me confused with TULS. I am Ryan Spillman.

 

here's a reason, more boost=more heat, and intercooler space under our bonnet isn't exactly abundant. Also, as others have stated, more boost=higher cylinder pressures=more stress on the pistons and rings.

If you are turbo'd, you are flowing WAY more air than the stock head was designed for, and the fact that it is a bottleneck will become way more apparent.

Sure, turning up the boost will have a SIMILAR effect on the dyno as far as power output, but the inherent added efficiency of a ported head will shine even more on a higher boost application in terms of power as well as reliability and IAT, which will allow you to run more aggressive ignition timing. Its a win win.

 

Ryan-No I knew it was you, I just can't remember people's first names

Thanks for the advise on the fueling system.

 

Good points. I will be running water to air so it will cool the charge much better than the stock A-A.

 

The water to air is a great idea. Allows you to run much shorter intercooler piping. Which in turn allows a lot faster spool up. Not sure if it will drop intake temps enough to allow you to run that much boost on 91 octane. Just watch the knock sensor and creep the boost up incrementally.

You can speculate all you want but you won't know until you try it.

If you are running a stock ignition system be ready to drop the spark plug gap down a lot.

 

Pretty big over statement...


the factory pistons are not a good choice if you plan on making REAL power.

The factory mini pistons WILL fail at around 250-265 whp... its proven.

so factory pistons are perfect for hp levels bellow that but... if as soon as a turbo enter the mix... or nitrous... you NEED pistons.

 

::insert whitty comment about m62 and blown pistons discussion here ::

/popcorn

 

LOL!!!!! im refraining... believe it or not...i try not to stir up to much "trash talkin"

but that motor blew do to bad tunning... no pistons will survive a bad tune

 

Thanks for the input Justin

After the input here I think the money will be well spent on the head. I just can't get that twinged out of the back of my head that it is a mistake not to do it...now about that full fuel system...........Brian, are you listening??

 

I've got over 15000 miles, numerous track days, and countless hours on the dyno with my turbo mini with no failures of any kind. I'm running a factory ecu that I've recalibrated and in street trim OBD2 legal the car makes 303whp with no issues. I've gotten much more power with an after market ecu system but then it's not street legal. The blown up Minis that have come to my shop for repair have suffered catastrophic engine failure mostly due to improper tuning and setup rather than faulty or poorly designed OE engine components.

 

Not any revolution in info here. It is always about tuning, any bonehead can bolt up parts and make power. The real issue is in making said power safely for the engine.

Won't be too long and I will be ticking away the miles on my turbo MINI!

 

Fast moving thread.

Put simply, increasing boost will increase cylinder pressure and thus the loads on rod bearings, main bearings, head gaskets, heads, pistons, rings, rod, crankshaft, and block. It seems on the MINI that stock pistons are most likely to fail first due to limitations on land strenght, but the added cylinder pressure will also accelerate wear on the rod and main bearings. Other components may (or may not) have much more margin.

Flow improvements (not necessarily just volume increases) can improve engine output by reducing pumping losses. Depending on how the headwork is done, combustion efficiency can also be improved through better fuel atomization. Stiffer valve springs can increase parasitic losses, and may impact cam lobe and follower wear, but may be necessary to keep from floatings valves depending on valvetrain mass and rpm.

If the head is machined to increase combustion, that's just another way to increase boost (technically not boost but the effect is the same on all the parts noted above). By increasing the static compression ratio, off-boost may be improved.

All of the above is generic, and doesn't take into consideration the effects (positive or negative) of "tuning". There is no such thing as a universally optimum solution.

Scott
90SM