Camshaft grinds for turbo

scott the viking · Post by **scott the viking** » Mon Dec 11, 2006 11:13 am

I have noticed quite a number of post that are in relationship to camshaft choice for forced induction cars. So I thought I would do a quick blurb about camshafts and turbo engines. This will be a generalization, just to give you a couple details.
First I would like to say that I know MANY of you are not running a turbo specific camshaft AND I know that your engine runs just fine with it. This post is not about what CAN be done but rather what SHOULD be done to get the most out of your turbo charged engine.
This is also not about race engines, but rather a street car, or even an off-road buggy.
Don't worry...I'm not going to drone on for hours about camshaft dynamics...this just a short statement...

What works as a cam in a pumped up non turbo engine, can create hindrances in a turbo charged engine.
In example...a large "lumpy" cam in an NA engine has a lot of a thing called overlap. As many of you know...overlap is the event where both the intake valve and the exhaust valve are open at the same time.
What has happened is the piston moved up the cylinder and is shoving the burnt gas out of your exhaust valve. The next thing that is going to happen will be your intake stroke where the intake valve opens, the piston goes down in the bore and "vacuums" fresh air and fuel in behind it as it goes down.
However...on an NA engine, pulling in fresh gas and air is not up to the piston alone. This is where overlap comes in. The piston just shoved the waste (exhaust) out of the exhaust port, the exhaust being pushed out the exhaust valve is going fast enough that it creates a vacuum behind it...kind of like when a semi truck passes you on the freeway and you can feel the vacuum behind it. This vacuum created by the exhaust rushing out the exhaust valve into the exhaust system is used to help pull in fresh air and fuel from the intake valve during overlap. There are a ton a variables about this and like I said....I am not going to go into all of them...you get the idea of what overlap is and what it does.

Now... a large amount of overlap on a turbo engine can cause you some grief. The reason is.... that the back pressure in your exhaust system created by your turbo can be twice as high (or higher) than the pressure in your intake...because your turbo is really in the way of your exhaust leaving the system. So lets say the pressure in your exhaust system is 20 psi and your boost pressure coming from your intake is only 10 psi. You open the exhaust and intake valve at the same time and I can tell you that your exhaust gas will go through the valve with only ten pounds of pressure fighting against it rather than the valve with 20 pounds fight it. Which forced exhaust gas back up through your intake valve.

This is only one tiny example of why a turbo camshaft is different from one geared toward an NA car. Like I said at the beginning...I don't want to bore you to tears with a bunch of tech talk...Just wanted to give a quick "heads up" that there is a reason that "turbo grinds" do exist.

I would like some of the guys on here to weigh in on this and possibly add a few details and reasons behind turbo specific cam design.
Also...any questions from guys that feel "lost" in this area will be answered in as plain, untechnical lingo as I can.

mschilling · Post by **mschilling** » Mon Dec 11, 2006 3:12 pm

Thanks for the topic. After having not so good a time trying to tune my EFI/AJ turbo 1776 with stock valves/ported heads and a good ole Engle 110, I was told to get a new cam. Webcam special order .455" lift @1.1 242 deg @.050" 280 deg on 112 deg lobe centers. It's also going from the old semi-hemi 7.0:1 heads to some new 044's with more CR and squish. Should be interesting to see the difference. Maybe stroke it while it's apart too.

mschilling · Post by **mschilling** » Wed Dec 13, 2006 6:52 pm

I'd like to hear a poll of all the cams used in turbo motors here.

Post by **seabeebuggy** » Wed Dec 13, 2006 7:08 pm

I use the tcs 20. with 1.25's duel 44 idf's

Howie · Post by **Howie** » Wed Dec 13, 2006 7:11 pm

I run an Engle K-65 cam with 1.40 rockers. 278 duration, .341" lift at the cam, 20 degrees of overlap, 108 LC.

Adding it's FI.

mschilling · Post by **mschilling** » Wed Dec 13, 2006 8:07 pm

Also what intake system carb or fuel injection. And your cam's specs if you know them would be helpful.

MinamiKotaro · Post by **MinamiKotaro** » Wed Dec 13, 2006 10:03 pm

I use a TCS-20 with stock rockers. It has gobs of low end but dies above 6000 RPM. I don't know if I'm going to try 1.25s or a new cam.

Buggsy · Post by **Buggsy** » Thu Dec 14, 2006 3:31 pm

Engle W100 on 114 lobe centers. The intent was to try to get the old Kads to idle smoothly. Apparently, nothing you can do to get Kads to idle smooth at 800 rpm. I have a 2332 blowing through Kads in a 1300 pound F/G street buggy. The cam works fine. Fierce up to 6000 rpm but I get lower ETs shifting at 5500. A real pleasure to drive around town.

Hotbugsy · Post by **Hotbugsy** » Thu Dec 14, 2006 5:24 pm

2387 Holley Draw Thru setup . Web Cam # 122/125 .506 int / .478 ext on 105 LC Cb 044 Heads Pulls well over 7k

Marty · Post by **Marty** » Thu Dec 14, 2006 5:53 pm

Custom grinds

Post by **david58** » Thu Dec 14, 2006 6:43 pm

"I was going to have scott the viking make me one...but he has quite a long waiting list. Others have said it's well worth the wait.

Matt Davis · Post by **Matt Davis** » Thu Dec 14, 2006 8:21 pm

Custom Pauter roller - Bigger than an FK-89 - Elec Injection

fuey22 · Post by **fuey22** » Thu Dec 14, 2006 9:36 pm

here we go with the secret custom b.s.

i got a quaddroople custom, triple ground, double degreed ...awe heck i don't now what i have.......

Mabbo · Post by **Mabbo** » Fri Dec 15, 2006 2:32 am

im using a web 110 with 1.25 rockers and it seems good... but iv never had another turbo engine 2 compare it against.

i have that in a 1955cc engine, with megasquirt controlling squirt and spark... not tuned properly yet

mike thompson · Post by **mike thompson** » Fri Dec 15, 2006 4:08 am

1600 motor-
CB cheater cam (specs out like a stock cam w 1.4 rockers and like a generic 270 degree cam for a v-eight) nice street cam, a little more pull than a stock cam with about the same rev range (pulls to over 5500), much noisier than stock cam, can only compare it to a stock cam and a 110 - hated the 110 because it was a dog until 2500 rpm driving around on the street - had to hold the engine shift points to keep up with traffic.

Mike