What is the best cam profile for turbo application?!?!?

Discussion pertaining to positive pressure E28s.
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5timesturbo
Posts: 288
Joined: May 26, 2013 3:24 AM
Location: Fayetteville, Ga

What is the best cam profile for turbo application?!?!?

Post by 5timesturbo »

Like the title states....I’m going to my stage 3 setup and I’m thinking about including a cam. I’ll be running mega squirt, intercooler and I’m not sure what size injectors yet. I would like to get a nice daily/track driving 600hp. Maybe not be at 600 everyday but track days can be long. Anyway any suggestions is appreciated.
Preyupy
Posts: 271
Joined: Jun 21, 2012 12:48 AM
Location: Issaquah WA

Re: What is the best cam profile for turbo application?!?!?

Post by Preyupy »

Most of the testing I have seen done over the years show that there isn't much difference between a N/A cam and a "boosted" cam. What makes a cam better and/or worse N/A does just about the same thing boosted. More lift and duration moves more air under all circumstances, big thing you will notice is the loss of a smooth idle when you start getting a lot of overlap. The really big cams are usually designed to make their power in the high RPM range (6000-8000 rpm) with an appreciable loss of low/midrange torque. Most Turbo engines don't rely on high RPM to make their power (a turbocharger that can efficiently flow enough air for an 8000 rpm engine usually is so large that the LAG at the lower rpm makes it very hard to drive). Also the high overlap cams are not as fuel efficient as they tend to allow more unburned air/fuel to pass right through the combustion chamber when both valves are open.

I would choose a mild or mid range cam for a Turbo application. Make sure you check your valve springs! The intake springs need to withstand the extra load of your boost pressure (a 46mm intake valve is roughly 2.5 sq/in so 10 psi of boost is exerting roughly 25lbs of force trying to open the valve for instance).
Rust Bucket
Posts: 85
Joined: Dec 27, 2020 1:06 PM
Location: Montreal

Re: What is the best cam profile for turbo application?!?!?

Post by Rust Bucket »

I had a quick look at your other thread.I assume you have a forged bottom,stock head,stock intake manifold.Not sure about the turbo manifold.

I have a thread on Speed-Talk(a place where engine builders discuss)about turbocharging the M30 and camshaft came on topic,of course.
I have all the OEM M30 camshaft at my disposal and intent to send one to the regrinder.There is no doubt the B35 camshaft is the best for
turbo application simply because it got the biggest lobe separation angle,meaning very little,none or even negative overlap.And plenty lobes
left for your desired profile.

Boost can further the torque curve higher in the RPM,to a point.The M30 is a formidable torque machine,and does spool a turbo rather quickly.
A more agressive camshaft would bleed off that precious low RPM action and the head,in stock trim(you got B34 right?) cannot take advantage of
hi RPM action anyway.

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A guy on Speed-Talk been nice enough to compute something ressembling my M30(3400cc quenched hemi inline six with pitiful flow numbers and
a very restrictive turbo log(using 745i stuff),on a engine simulation software.This in turn gave us a desirable camshaft profile.Intent of this cam
is not to turn the M30 into a screamer.It's intent is to allow the M30 to deal with a generous quantity of boost.Which from the little I know about
your build is what you should aim at.

Here's the link to the thread: https://www.speed-talk.com/forum/viewto ... 15&t=63857

Been a while I looked at it but from what I remember,you want the B35 cam,advance it(adjustable cam sprocket) and have the intake opening
lobe ground if needed,depending how much you advanced the cam.Take it for what it's worth,this is rough data.Everybody more than welcomed
to discuss this.

I have two build on the shelves,one is my M106 I intent to make a responsive engine(fast spool)for a manual car.Second build I have three M102
waiting to be destroyed for science.These will be heavily ported,port floors will be epoxied and reshaped,zero fack given under 3500RPM.
It will use a automatic transmission(2004r) with a stall and a 50hp nitrous shot if needed.

The first engine use M30 attributes,low RPM torquey engine with good mixture motion.Stockish head,intake manifold,not so much porting.
The second engine(s),does not use M30 original attributes,will need intense porting,custome intake manifold,lots and lots of research and
you are pretty much on your facking own,this is no 2JZ with tons of knowledge and support,when wanting to push the enveloppe.

I'm getting off bat here but there it goes.From what I know about your build,that is forged bottom and stock heads.If you wanna go the
next step,you need the latest,baddest turbo.I guess you have ARP headstuds and a good gasket,oringed block or head.Get that B35 cam and
have it ground a couple degrees on intake opening and advance the cam a couple degrees,dunno how much.Have a good valve job done,
might want a little bowl job done,do not enlarge intake ports.Exhaust valve are suceptible to burn and crack,might want to upgrade.
5timesturbo
Posts: 288
Joined: May 26, 2013 3:24 AM
Location: Fayetteville, Ga

Re: What is the best cam profile for turbo application?!?!?

Post by 5timesturbo »

Sorry for the delay in reply...I was checking the thread for about two weeks and got no response...so I gave up. Thanks for the advice!! As for the hat I’ve got planned so far: 8.5:1 turbo pistons, TCD manifold, forgot the turbo, and ofcourse mega squirt. I’ve talked to Ireland engineering and they’ve got a 270 cam that seems mild enough to work.... How does that compare to the b35 cam?? I’m possibly willing to go the cam adjustment route...I’d just need more info and someone to walk me through what needs to be down to get the results I’m looking for. Valve springs, valve guides...ARP everything is a no brainer if you want to do it right from the start. Any other suggestions I appreciate it. It’s winter....engine building time. Lol
Rust Bucket
Posts: 85
Joined: Dec 27, 2020 1:06 PM
Location: Montreal

Re: What is the best cam profile for turbo application?!?!?

Post by Rust Bucket »

I am putting lots of toughts,I guess you could call that R&D,on porting the B34 heads I got.Some will be sacrificed for science.I have a couple B35 heads too,arguably these are better,most notably on the short side as can be seen on pic I posted comparing B34 and B35 ports.Since you are using forged pistons with a tiny bit higher compression ratio,you could use said better B35 heads.You would need oversized valves if you choose to have a good valve job done,which I reccomand.Might as well put quality exhaust valves while in there.

I have a world reknown head porter not far from where I live.I am about to pay him a visit to see what he can do for me and my modest budget.
I probably would have him test different things I'd do myself at home,on his flowbench.But dont hold your breath for it.

You have to decide if you keep stock intake manifold or not.Look at the drawing I posted earlier.

-Camshaft basics-

Duration,lift,overlap,LSA,assymetric lobes yada yada yada...

In the end,it is only the four valves events that count.The M30 in its original for does not benefit from higher lifts as would,for say,a SBC would.
You also have to pay attention to ramp angles,so that valvetrain follow the cam gently.The stock M30 rocker arm design lend itself to aggressive
ramp opening or closing so I have heard.Not sure which.

Valve opening:You are using a log turbo manifold and this engine is no high rpm screamer,you dont want overlap,you are not in a hurry to open the intake valve so much.I guess you could compensate late intake opening with agressive ramp.Combined with good seats angles.

Valve closing:Arguably the single most influential valve event.Late intake closing means intake charge has time to turn around and exit cylinder past intake valve back into intake runner.You dont want that.Late intake closing is for hi rpm powerband.You want low rpm torque,that will spool the turbo.You want early intake valve closing.Advancing the cam does just that.

Exhaust opening and closing:I would need to revisit,from what I recall,a stock B35 cam with a a bit of advance is just fine.Might want a gentle opening ramp since the valve opens against great cylinder pressure.Might want a bit more lift.As agressive closing as valvetrain allows.You want
no overlap,remember,you are not in a hurry to open intake.There is still exhaust in the cylinder left,it did'nt disappear magically.There is not so much scavenging.In fact,another cylinder is in full blowdown in the compact log manifold.It is not hard to imagine this pressure wants to enter the
cylinder.That is why the B35 cam is the preferd choice,it got the greater lobe separation angle of all the OEM camshafts.I am still debating prefered exhaust closing time.There is your homework.

I dont know the depth of your wallet.I'd find a couple B35 heads if I was you.Send the B35 camshaft to DeltaCams.

A well tought valve job,bowl blending,depending if you keep stock manifold or not.

I never turbocharged M30 so far,or any car for that matter.Take it for what is worth.But from what I understand,you dont want duration,you want to spool a bigger turbo. You'd also save a couple hundred bucks going the regind route.

My .02$ (edit format,originally written on my phone)
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