Camshaft choice for B21 with TB41 turbocharger

[Stefan Ingi Jonsson]

Hello, sorry I have to write in english, I live in Iceland so its either english or icelandic
Our car is used for drifting and we need more power from the motor and we need some advice on what we can improve because we feel like the car is producing 350 hp max at 1.6 bar so we are thinking that we are doing something wrong .

Perhaps the camshaft is the bottleneck and maybe a new camshaft would help this engine

We have a B21A with the following setup:

Running on 98ron.
8.3 compression ratio.
3mm headgasket from klracing.
Homemade twinscroll exhaust manifold(38mm ID and 50cm tubes 1-4 and 2-3).
Plenum intake from KLracing(cheap one).
KG2T camshaft.
Double valve springs.
38 exh and 46 int valves.
H-beam conrods from cxracing.
Stock B21A pistons(the pistons and conrods are equal in weight +-1g).
Head ported lightly.
Garrett TB41 Turbo.
Turbine wheel 73mm ind 63mm exd.
compressor 51mm ind 76mm exd.
Turbine housing is ar 1.15.
M90H gearbox.
3.73 stock volvo rear.
Intercooler(45cmLength 30cmHeight 7cmWidth)
2.5 inch intercooler piping.
3"open exhaust 3 meters in length.
76mm throttlebody.
970cc at 3 bars bosch injectors with extended tip.
Megasquirt 2 using original lower distributor hall sensor setup.
Backpressure measurement at the collector 0.8 bar max at 1.35 bar boost(we have run the engine at 1.6bars but did not measure backpressure then.
Backpressure measurment after turbine 0.1 bar max.
Compression test is 164 at cyl 1, 160 at cyl 2, 155 at cyl 3, 151 at cyl 4
EGT is around 820c at full load and 470c at idle measured at the collector.
Wastegate opens at 4000rpm in 3rd gear.
We have gone up to 7500rpm but the power goes down from 6500.

Here is our ignition map: https://imgur.com/4RQP7bT
Here are some pics https://imgur.com/a/7Cb9oG0
Our youtube channel: https://youtu.be/IY8E5xh4OCA

[Allx]

A GTX3071 or similar will do magic for you. Smaller turbine and bigger compressor will raise both torque and power

[whilliam]

No, Totally wrong!
A smaller turbine could only give you LESS power! What a smaller turbine is thought to do is making the turbo spool quicker. The ones predicting that is the turbo-manufacturer but they are also a little wrong.
Making turbine WHEEL smaller will give you faster spool by more/earlier use of the axial-part (exducer area) but, instead, if making wheel bigger AND making the housing smaller will make the radial- part (inducer) to come on earlier and as a benefit from big turbine exducer you will have less back pressure at high revs.

A turbo with smallest possible A/R and BIG wheel will giva a little more expensive turbo (higher cost for material) but it will always give you the best power band.

Your turbo has good dimensions for 450 Bhp on petrol (E85 will give you 10-15% more) Maybe the A/R is a little big but if you are happy with spool it should not bother you. Unfortunately the design of the compressor wheel is old, a more modern will give a little better result (but the dimensions, 51x76 is good)

Some questions to help you out:
1. Specify your exactly boost @ the 350 Bhp
2. 350 Bhp max at what rev. ?
3. Maximum torque at rev. ?

The best would be if you make us a "list"/table with Boost and torque figures att every 500 rpm from 3500 to rev. limit.

[quattro]

Regarding the camshaft I don't think for a minute it can be a bottle neck. Open/close would be like 36/84 degrees which sounds like a decent compromise between low speed driveability and high speed power. It's not wild, but respectable and adequate, I would say.

But 1.6 bar is too little boost. The turbo compressor wheel has a low trim which means it is designed for high boost figures. The turbine wheel is big and your A/R is fairly big as well - all these three in combination means that you're not getting the best our of your turbo.

I think you should try to find a turbine housing with substantially lower A/R. 0.85 or even lower than that. If that is difficult to find I think you should try a turbo more in line with what Allx is recommending.

Then, looking at your ignition map, I wonder if you have had the engine run on a dyno. 1. You have a lot of columns down the rev range where the engine is not supposed to be working hard at all. But in the range where things are supposed to get serious you have hardly any possibility of a detailed mapping. 2. The ignition degrees at higher revs seem to be quite cautious.

So, to sum it up. My view is that you are not working your turbo hard. It has a lazy life. And you are not working your engine hard either.

[whilliam]

I agree with quattro, but i have not checked your ignition map. I would like to calculate your result regarding Boost/torque - curves. After that i can give more specific information about your whole setup.

My fist reaction was that your boost is too low but i did not write so because i do not know if the boost is even lower at the point where max Bhp occurs.

You should change nothing until we see the whole situation, after that we can look att points to improve and, probably, you want to spend as little effort and money as possible, to achive your goals - that is why we should not start to "switch" components before we used the ones we have to a decent level.

[Stefan Ingi Jonsson]

The link in the post is wrong, it is fixed now. Here is a video of the project my brother made if you are interested. We will post more on this channel in the future. https://youtu.be/IY8E5xh4OCA

We will do a dyno session soon and post the graph here and hopefully we can squeeze more power out of this setup with some tweaks.
Do you want hp, torque and boost on the graph?

@Allx We do not need better spool, we need more top end power at around 7000rpm but maybe a GTX3071 would work better with this camshaft (KG2T) because the boost would match the powerband of the camshaft? What camshaft would then work well with our turbo? Maybe K or STS247 from Jens?

We are grateful for your help!

[whilliam]

The graph needs to show torque, boost and rev. then it is possible to calculate how well the set-up is using the boost.

A turbo is just a device for making air more dense, that function is not magical and has nothing to do with the camshaft (if you feed the engine from a free source of boost, it will appear as a normally aspirated)

The magic around turbos is to make them rob as little energy as possible from exhaust (if max power is the only goal) and if we should also have a good powerband from the bottom more magic is needed.


A bigger, more free flowing turbine will ALWAYS give more top-end and that is regardless from camshaft. You can earn nothing from trying with a smaller turbine.

From another point of wiew the camshaft choice is helping you with around 20-40 Hp on top but the turbo choice will give you almost what ever you want.

[Allx]

So if he takes that new design Gen2 650hp turbo and replaces the old 450 hp dieselturbo, it will give him less power?

The turbine will probably be really good on a 65mm turbo making 800 hp.

[whilliam]

Allx, i do not know your age or what you have seen so far, regarding the turbo tuning business. But i can tell you one important thing: Garrett have not built a turbo, not for many years now and i do not recon that they ever did, that is made to outperform others. (they build their turbos to maximize their share holders profit)

Another important thing to concider is that the materials and "design" is worth nothing compared to dimensions - this means that an old turbo ALWAYS will outperform the new turbo if the old one have perfect dimensions and the new is wrong/random.

In fact the turbos of today is better than old design only by a few percent:
Turbine housings: about the same as the old ones with a few old better than todays turbos (and a few old really worse/bad)

Turbine wheels: todays material sometimes better (will give you thinner blades) but the dimensions today is most of the times not so good (to save money) My judgement will say around 1-2 % better today than 20 years ago.

Bearings: Ball bearing or what ever you like? The best system today will save about 1% compared to old style but most of the ball bearings will crack when you "race" them - if explanation is needed i will give it to you in another occasion.

Compressor housing: The design of the housing will give little difference to performance. The really old ones "torus" housing is not so good and differences between the "normal" ones is also in the 1-2% region and the biggest difference occur in sizes (low boost and early spool is best with a big one and the small ones should/can be used at high boost)

Compressor Wheel: Here is the BIG difference between the new/old but anyhow the difference is only in in the 3-5% region if we compare well dimensioned wheels.

The turbo we have here contains a turbine side that will reach 800 Bhp on the right engine and fuel (combined with a good compressor side).

The turbo from your suggestion is not an 800Hp item, it will stop att 10% less and maximum 750 Bhp. if you squeeze it further it will eat its bearings in no time and even for 750 Bhp it will need a bigger engine and less boost (we need to dump a lot through waste gate)

One turbo is designed for diesel and the other is for an engine like Supra 2Jz, the Volvo could not time up with any of them but turbine - wise the old one is the best for big Bhp, we need all the knowledge we could get to see which one is best on the Volvo engine and the turbos is really different one is "oversized" at compressor and the other is undersized (if we want more than 450hp)

Please take notice of that one turbo has 55mm exducer and the other 64mm.

Future will tell what the dyno will give and what to do for maximizing the performance of this car, one comment that tells a lot is that the compressor wheel is T04B type and Garrett could have given the turbo a T04E instead, the T04E is less prone to surge and is performing better at high boost, this turbo could benefit a lot from an aftermarket billet wheel.

[whilliam]

Regarding the explanation above: I never finished why the 6-10% better opportunity for performance on the newer turbos could sometimes be outperformed by an old turbo.

Today, many customers just "buy" their turbo from a shop that could not calculate dimensions, they buy a turbo that "should" be good if you look at all the promotion from suppliers.

When this "random" turbo is put on the engine it is not uncommon to see it is 20% off in it´s dimensions, many times it is 20% off if you look only at the compressor map.

Here is the reason for me to say that design and material is worth nothing if the dimension is wrong.

Please look at it from another point of wiew: if the turbos of today was that good that many people think WHY is there not just ONE turbo that fit us all?

[Allx]

Nice explanation. But you never said anything on the mismatch of that old turbo for what it is used for.

It was the turbine of the TB41 i meant was good for larger compressor.

The TB41 is probably nice if you install it on a chevy small block with a goal of 350 to 400 hp. They are having problems with loosing power at the top end we know that the turbine is good for double the hp. So it must be something else.. Right?

I was just giving him an example of a turbo that has a turbine that will spool many times faster and a compressor that flows well enough for them to not loose airflow at 7000 rpm.

[whilliam]

The thread starter wanted more power. You throw him a "random" not calculated, turbo suggestion. The turbo you mentioned is not a good match to his engine, and that is in many ways (both physical fitment and function-wise) On top of that it is not cheap. Next, you did a statement that is not true.

If we should recommend a turbo switch (or upgrade of the one he sits on) we must at least do a serious calculation ( it must be better if the turbo he buys is really better than the one he have)

i think he is not using the turbo right (boost curve and mapping) Quattro thinks the same, i think Quattro also is curious what the new dyno session will tell and after that we can recommend him a lot of things.
Oh, I did forget, we must know his goal as well, is it beyond what his compressor is capable of then we must change.

Nice explanation. But you never said anything on the mismatch of that old turbo for what it is used for.

If i get you right here, you think the TB41 is mismatch internally, well it is not. The only way to mismatch a turbo itself is by putting wheels to it like you suggest, as long as the turbine side outflows the compressor, the turbo is in good match.

Another thing if it is mismatch to the engine, then the hotside could be to big and the result is poor spool, but that is not the case here and i mentioned it earlier.

I was just giving him an example of a turbo that has a turbine that will spool many times faster and a compressor that flows well enough for them to not loose airflow at 7000 rpm.

It is not this easy with turbos, you can not mix what ever turbine to what ever compressor and think it will work in both ends. Main reason for good spool is a perfect match between compressor and engine, this means that the compressor is working in the center of its map (where it use the least energy from turbine)

Since power from engine is low during spool, the turbine could not extract so much and that is why the compressor must be a match (and not robbing all power to make hot air)
Next, you think that a small turbine wheel (like Garrett BB) is good for spool, well, it is not. If you build the turbo with mechanical gearing (this is when the exducer on the compressor is bigger than the inducer on the turbine) it can not use the pressure (audio) pulses from the engine as good as a big turbine could.

Every time somone tried to build a turbo with enormous turbine wheel and super small A/R on the housing, we have seen good results. By good i mean in top -class of the world and always combined with a nice power band starting really early. We have not seen too big a wheel yet, but we will try bigger until the curve goes in the wrong direction.

[Allx]

What statement was not true? You think that i meant that a smaller turbine will give more power?

I would never have thought that someone would not recommend throwing an old dieselturbo in the garbage. From what the threadstarter describes it is almost the same as the 18T turbo on a B230 with agap (maybe) camshaft that I tuned today. VE falling of after 6200 and around 330 hp at 1.5 bar of boost.

[Steve]

I may be reading to quick, but it feels like there is some information missing?

Has it even been on a dyno before?

because we feel like the car is producing 350 hp max at 1.6 bar

And if it has, is 350hp@1,6bar bad for a B21 on 98?


Did you try to add more boost?

[Stefan Ingi Jonsson]

Steve I have not measured the engine on a dyno but that is the next think I will do, it will be fun to see the actual numbers.
About the boost, I have never tried to go higher but after I changed the wastegate setup from two 38mm to one 40mm there is a little boost creep that has gone almost up 1.8bar in 4th gear when the wastegate was set to around 1.1 bar and it was fine just more power.
Allx the compressor keeps full boost all the way up too 7500rpm and I can hear the wastegate is still open and no extra backpressure so I dont think that it is a problem.

Thanks again for great response everybody