Forced Induction Cam questions?
Thread Starter
TECH Apprentice
Joined: May 2010
Posts: 361
Likes: 0
Forced Induction Cam questions? Ok so when it come to forced
induction cams some are marketed blower or supercharger cams and others as turbo cams. What’s the real difference between a cam for turbo setup vs supercharger?
induction cams some are marketed blower or supercharger cams and others as turbo cams. What’s the real difference between a cam for turbo setup vs supercharger?
Last edited by Drj8787; Sep 29, 2018 at 09:29 AM.
Supercharger cams typically bias toward the exhaust helping expel the spent charge since the intake is force fed in. So you'll see cams with 10 degrees or more split for them. PD/roots blowers typically have even more than that since they create a lot of boost early and throughout the range. Centrifugal superchargers add boost as the RPMs climb, so they can be a little less biased... but typically have a large amount of advance to open the exhaust valve sooner than the duration would otherwise dictate, aiding with high RPM range function.
Turbos are cammed a lot like NA cars if the backpressure/boost ratio is 2:1 or less... 1:1 would be cammed the same as an NA car. The further you get away from a 1:1 ratio, the more you have to relieve the exhaust/turbine issue. So you see a lot of single pattern or even reverse grinds in turboland for less efficient builds.
Overlap makes power even in a turbo/supercharger build. It just pushes the operating range higher (just like an NA car). But you can get away with minimal overlap and still make crazy power. So, one of the advantages for street FI builds is the ability to retain stock-like manners while making more power.
Turbos are cammed a lot like NA cars if the backpressure/boost ratio is 2:1 or less... 1:1 would be cammed the same as an NA car. The further you get away from a 1:1 ratio, the more you have to relieve the exhaust/turbine issue. So you see a lot of single pattern or even reverse grinds in turboland for less efficient builds.
Overlap makes power even in a turbo/supercharger build. It just pushes the operating range higher (just like an NA car). But you can get away with minimal overlap and still make crazy power. So, one of the advantages for street FI builds is the ability to retain stock-like manners while making more power.
Thread Starter
TECH Apprentice
Joined: May 2010
Posts: 361
Likes: 0
Supercharger cams typically bias toward the exhaust helping expel the spent charge since the intake is force fed in. So you'll see cams with 10 degrees or more split for them. PD/roots blowers typically have even more than that since they create a lot of boost early and throughout the range. Centrifugal superchargers add boost as the RPMs climb, so they can be a little less biased... but typically have a large amount of advance to open the exhaust valve sooner than the duration would otherwise dictate, aiding with high RPM range function.
Turbos are cammed a lot like NA cars if the backpressure/boost ratio is 2:1 or less... 1:1 would be cammed the same as an NA car. The further you get away from a 1:1 ratio, the more you have to relieve the exhaust/turbine issue. So you see a lot of single pattern or even reverse grinds in turboland for less efficient builds.
Overlap makes power even in a turbo/supercharger build. It just pushes the operating range higher (just like an NA car). But you can get away with minimal overlap and still make crazy power. So, one of the advantages for street FI builds is the ability to retain stock-like manners while making more power.
Turbos are cammed a lot like NA cars if the backpressure/boost ratio is 2:1 or less... 1:1 would be cammed the same as an NA car. The further you get away from a 1:1 ratio, the more you have to relieve the exhaust/turbine issue. So you see a lot of single pattern or even reverse grinds in turboland for less efficient builds.
Overlap makes power even in a turbo/supercharger build. It just pushes the operating range higher (just like an NA car). But you can get away with minimal overlap and still make crazy power. So, one of the advantages for street FI builds is the ability to retain stock-like manners while making more power.
Single pattern would be 222/222 and reverse would be 226/222 @ .050".
The lift (your example is lift) doesn't have a lot to do with whether it is a single or reverse or traditional split--lift is a function of the lobe design. However, lobe design can make it single pattern off the seat, traditional split @ .050 and reverse at .200 depending on the ramp/lobe intensity/lobe design. But typically, you want a stable, softer lobe on the exhaust side that closes the valve in a controlled manner. Most of the off-the-shelf cams do that nowadays. And are fine for the vast majority of users.
The lift (your example is lift) doesn't have a lot to do with whether it is a single or reverse or traditional split--lift is a function of the lobe design. However, lobe design can make it single pattern off the seat, traditional split @ .050 and reverse at .200 depending on the ramp/lobe intensity/lobe design. But typically, you want a stable, softer lobe on the exhaust side that closes the valve in a controlled manner. Most of the off-the-shelf cams do that nowadays. And are fine for the vast majority of users.
Trending Topics
TECH Apprentice
Joined: Apr 2012
Posts: 333
Likes: 4
From: New Zealand
Forced induction engines require the same camshaft your engine would use N/A, there is no reason to change cam profile for a forced induction set-up, this has been proven by Darin Morgan and others with a crap load of testing and top of the line equipment. What ever makes the engine run the best N/A is what you use with a blower or turbo, it doesn't matter. You are not changing cylinder volume / cid of the engine, you are only changing air density..
lolz. That statement is not going to sit well with a bunch of folk. It sits well with me as a general rule, however there are combos that do respond to turbo/blower type profiles. It may not affect peak power for the reasons you said - but it can affect spooling and area under the curve... and this is why some will opt for a faster spooling, better driving, fatter power curve cam, then simply add 1psi to get the top end power a tighter LSA NA cam would have made. My 2 cents, and boy can I be wrong. The LS3 (stock heads and intake) is the perfect turbo engine as it does not like overlap anyway and this is why you see aggressive cams at 224-227 (@ 050) with little split making about the same peak but much fatter curves as a 230-235 with big split
Last edited by Bazman; Oct 2, 2018 at 05:57 PM.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo Thread Starter
TECH Apprentice
Joined: May 2010
Posts: 361
Likes: 0
I'll take the advise of Darin Morgan and other engineers that have looked into this subject, Darin Morgan said that every time he changed the profile away from what the engine required N/A he lost power.. People can say i'm wrong all they want but I am just saying what Darin Morgan said, and I guarantee he knows more about this subject than any of us on here..
So, a 75mm turbine housing on a 408cid motor will want to be cammed like the 408 would otherwise want to be cammed NA? The answer is ha hell no.
As I said, you have to take into account the combo and spec for it. A bad turbine setup is not going to respond the same way a pair of twin 66s would on that 408. The twins can be cammed like it's NA. Backpressure ratio is a key component.
Superchargers are more forgiving.
As I said, you have to take into account the combo and spec for it. A bad turbine setup is not going to respond the same way a pair of twin 66s would on that 408. The twins can be cammed like it's NA. Backpressure ratio is a key component.
Superchargers are more forgiving.
On The Tree
Joined: Aug 2007
Posts: 141
Likes: 2
Darin has been researching and designing induction systems for over 33 years. Throughout his career, his cylinder heads and intakes have been used in numerous disciplines such as NHRA Pro Stock, IHRA Pro Stock, Pro-Mod, Pro-Nitrous, tractor pulling, NASCAR, Land-Speed record engines, and much more. He has given over 37 lectures on wet-flow dynamics, cylinder head and induction system design, and induction system tuning. He has also taught over 50 engine building and induction system design classes.
TECH Apprentice
Joined: Apr 2012
Posts: 333
Likes: 4
From: New Zealand
All of that is true, and if you look at the dyno graphs they got their mountain motors to pull it is mind blowing how flat and how high in the rpm range their long stroke engines held their power.... anyone else trying to copy that would have seen a leg out of bed long before the redline Darrin got..... bar a small handful of fellow legends who also belong in a hall of fame.
That aside, I doubt he has ever been associated with a turbo setup producing a PR of 3:1 (like many here will have. for budget reason mostly). His combo's will all be efficient and will want an NA cam. Now if he has tested a single turbo 3:1 budget set up and found the same results I'll be first to say "great" - takes a lot of thinking out of my equations. I strongly suspect the inefficient high backpressure systems will bleed off a LOT of power/TQ under the curve in a high overlap situation that the NA motor will tolerate with decent exhaust.... the peak power may well be very good, but the soggy bottom end may be crap to live with daily. Just my concern, not my knowledge as I have yet to test cams back to back on this issue... plus I will never go back to 3:! setups lol
That aside, I doubt he has ever been associated with a turbo setup producing a PR of 3:1 (like many here will have. for budget reason mostly). His combo's will all be efficient and will want an NA cam. Now if he has tested a single turbo 3:1 budget set up and found the same results I'll be first to say "great" - takes a lot of thinking out of my equations. I strongly suspect the inefficient high backpressure systems will bleed off a LOT of power/TQ under the curve in a high overlap situation that the NA motor will tolerate with decent exhaust.... the peak power may well be very good, but the soggy bottom end may be crap to live with daily. Just my concern, not my knowledge as I have yet to test cams back to back on this issue... plus I will never go back to 3:! setups lol