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Will my Supra ever run?!!
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Forum Camshaft Tuning Info


On four stroke engines, it is important to realize that the cam rotates once for every two rotations of the crankshaft.

Volumetric efficiency is based on cylinder fill. If a 2.0L engine is filled with 2.0L of an air/fuel mixture, we say its volumetric efficiency is 100%. If a 2.0L engine fills with 3.0L of an air/fuel mixture, we say its volumetric efficiency is 150%. A forced induction engine will have a larger than 100% volumetric efficiency since the intake charge and combustion chamber are being pressurized. A naturally aspirated engine can also have a slightly larger than 100% volumetric efficiency, but it will only happen for a short duration, and is usually only in the peak of the powerband.

The art of designing camshaft profiles is meant to increase the volumetric efficiency in the RPM range that the customer requires. Camshafts don’t make magical horsepower from nowhere, they simply move the powerband around by changing the volumetric efficiency to attain the desired results.

The four strokes of the engine are:
Exhaust
Intake
Compression
Combustion
**The “start” is not important because it’s a CYCLE, meaning it repeats**

Looking at a camshaft, the sequence would be as follows:
The exhaust lobe pushes open the exhaust valve and the piston comes up to push the exhaust out, then starts to close. The intake starts to open, just as the exhaust is closing, piston goes down, and the intake valve closes. Then both valves stay closed for the compression and combustion strokes. This means that the first lobe to come through the rotation will be the exhaust lobe, immediately followed by the intake lobe.

Overlap is the point where the exhaust valve is closing, and the intake valve is just opening.

To increase overlap, you have to RETARD the EXHAUST, and/or ADVANCE the INTAKE.
To reduce overlap, you have to ADVANCE the EXHAUST, and/or RETARD the INTAKE.

Simple cam tuning rules for NATURALLY ASPIRATED engines:
Advancing both cams => more low-RPM power, less high-RPM power
Retarding both cams => more high-RPM power, less low-RPM power
Less overlap => more low-RPM power, less high-RPM power
More overlap => more high-RPM power, less low-RPM power

In a naturally aspirated engine, the extra overlap is called "scavenging". Scavenging is using the out-flowing exhaust to help draw in the next intake charge (partially causing lumpy idle).

Simple cam tuning rules for BOOSTED engines:
Advance intake and exhaust => more low-RPM power, less high-RPM power
Retard intake and exhaust => more high-RPM power, less low-RPM power
Less overlap => lower EGTs, faster turbo spool, less fuel
More overlap => higher EGTs, slower turbo spool, more fuel

Boosted engines don’t like overlap. The incoming cold air and fuel cools down the outgoing exhaust charge, condensing the exhaust gasses. This is VERY counter-productive in a turbo application since the engine needs no help from scavenging to fill the cylinder. I've heard this being called "turbo chill".

Cool, condensed gasses in the same space push less hard on the turbo, causing lag. HOT gasses are better at spooling the turbo, thus the advanced exhaust timing to open the valve sooner in the power stroke. This steals some of those hot, expanding exhaust gasses to help spin the turbo a little faster. When the piston is near the bottom of the bore, hardly any energy is going into rotating the crank anyway, so stealing expanding gasses won’t hurt anything. The retarded intake just helps cut down the overlap further.

Retarding overall cam timing:
Retarding overall cam timing is better for high-RPM power. This is because the valves are closing later. The intake valve is closing AFTER the piston has started to travel back up the bore for the start of compression stroke. This is terrible at low RPM because the intake air velocity is low, and air that was once in the cylinder is now being pushed back into the intake manifold and causing turbulence.

At high-RPM, the rules change. Air has weight, and thanks to Sir Issac Newton, we know that once it is moving, it doesn’t want to stop moving. This means that the air can continue to flow into and fill the cylinder, EVEN AFTER the piston has begun to travel UP the cylinder bore. This can allow an engine to exceed 100% volumetric efficiency, if even by a small amount.

Advancing overall cam timing:
Advancing overall cam timing is better for low-RPM power. This is because the valves are closing a little sooner. The intake valve is closing AT or NEAR when the piston is at the bottom of the bore for the start of the compression stroke. This is great at low RPM because the intake air velocity is low and easily affected by changes in the direction of piston movement in the engine. Almost as soon as the piston gets to the bottom of the bore on the intake stroke, the valve gets slammed shut so no air can escape as the piston begins to travel back up the cylinder on the compression cycle.

At high-RPM, this may become a restriction since the air has inertia and responds a little slower to pressure changes, potentially choking the air flow to the engine a little.

Conclusion:
This information is aimed at allowing tuners to understand what happens when cam timing is altered. When a larger duration camshaft is being installed, unless the lobe centerlines have been changed, the overlap will be increased. If installing larger camshafts in a turbo application, advancing the exhaust and retarding the intake will reduce the inherent increase in overlap caused by upgrading to a larger profile. Most cam grinders, especially regrinders, put the new profile in the same position as the old profile because it is easier, or the only way possible. This has to be changed when the cams are installed in an engine to attain the desired result.

A forced-induction engine should idle smooth when properly tuned, and a naturally aspirated engine should be “lumpy” and have a lope if it is tuned aggressively towards the high-RPM range. If a forced induction engine is loping at idle, fuel is being wasted, turbo spool time is being increased, and power is being lost.

-Dave Atchison
 

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Forum Camshaft Tuning Info

.......

A forced-induction engine should idle smooth when properly tuned, and a naturally aspirated engine should be “lumpy” and have a lope if it is tuned aggressively towards the high-RPM range. If a forced induction engine is loping at idle, fuel is being wasted, turbo spool time is being increased, and power is being lost.

-Dave Atchison
I was with you 100% until here - ;)

If you've got a forced induction engine loping at idle, you are not necessarily loosing fuel, spool time, etc - only because you're not taking into consideration exhaust flow.

I'd disagree that scavenging is unimportant on a forced induction engine - on the contrary, I would argue that proper exhaust tuning (and in turn, scavenging) is even MORE important than on an NA motor!

If your exhaust backpressure is so high that you are stalling the airflow out of the engine, then you've chosen a turbine side that is too small, or you don't have enough flow out of the turbine (needing bigger exhaust).

Some overlap is beneficial, even in a boosted motor, for the exact reason you stated - you have to get that spent air/gas out of the cylinder quickly, and at high rpm, you will lose a good bit of potential stroke to pull the air charge in, if you wait to open the intake valve (decreasing overlap)

Closing the exhaust valve earlier will only serve to partial dilute the mixture being drawn in.

Anywho, just me .02 :)
 

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Will my Supra ever run?!!
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Discussion Starter #7 (Edited)
I was with you 100% until here - ;)

If you've got a forced induction engine loping at idle, you are not necessarily loosing fuel, spool time, etc - only because you're not taking into consideration exhaust flow.
What do you mean about not taking into exhaust flow into account when an engine is loping at idle? Loping is caused by poor intake flow, not exhaust flow. Low velocity intake flow, or excessive overlap sucking the intake charge straight out the exhaust is what causes loping. Loping is due to a cylinder that's not filled enough to create a strong enough burn to cause a smooth idle.

I'd disagree that scavenging is unimportant on a forced induction engine - on the contrary, I would argue that proper exhaust tuning (and in turn, scavenging) is even MORE important than on an NA motor!
I would say scavanging is much LESS important on forced-induction engines (same, but different way of saying it). If you look at overlap specs on high-end forced induction cams, the overlap is cut back to less than 5 degrees, compared to about 25-30 on stock N/A cams, and as much as 80+ on performance N/A cams. If you're talking about turbo engines that rev to 10k+, I'll conceed that the intake velocities are reaching the point where scavenging is beginning to work on a forced induction setup as well, but we all know that 99.99% of street driven vehicles will NEVER reach this.

If your exhaust backpressure is so high that you are stalling the airflow out of the engine, then you've chosen a turbine side that is too small, or you don't have enough flow out of the turbine (needing bigger exhaust).
I never spoke about exhaust backpressure being so high that you're stalling the airflow. I stated that if you leave the intake valve open for too long (excessively retarded), when the piston comes back up, it pushes the air back out of the cylinder, and into the intake manifold, causing the INTAKE charge to slow or stall.

Some overlap is beneficial, even in a boosted motor, for the exact reason you stated - you have to get that spent air/gas out of the cylinder quickly, and at high rpm, you will lose a good bit of potential stroke to pull the air charge in, if you wait to open the intake valve (decreasing overlap)
The point of forced induction engines is that the boosted intake charge pushes the air in all by itself, not requiring the aid of overlap (in street RPM applications). You're also not losing any intake duration... you're just changing when you're doing it, so you wouldn't lose any measureable amount of potential stroke pulling the intake charge in (because it's being pushed), and you've still got the same fill time in crank rotation degrees.

Closing the exhaust valve earlier will only serve to partial dilute the mixture being drawn in.
Closing the exhaust valve sooner will cut down the overlap. When getting performance cams of ANY engine, the exhaust will always be the main power getter out of the two (intake vs exhaust). It will NOT dilute the next intake charge because you're using the exhaust charge to draw in the next intake charge (remember scavenging?). You're actually diluting the exhaust charge with intake, and that's what you're aiming to reduce (turbo chill).

Anywho, just me .02 :)
Thanks for adding to the thread in a classy, respectful fashion! I welcome all questions and comments, and the occasional respectful arguement as well! :)

1-2 clutch u said:
{wish I woulda payed you 30k instead}
I wish you woulda payed me 30k instead too :p .
 

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What do you mean about not taking into exhaust flow into account when an engine is loping at idle? Loping is caused by poor intake flow, not exhaust flow. Low velocity intake flow, or excessive overlap sucking the intake charge straight out the exhaust is what causes loping. Loping is due to a cylinder that's not filled enough to create a strong enough burn to cause a smooth idle.
Absolutely correct! I only brought this up to point out that what is best for idle isn't always what is best for WOT performance.

D-Dayve said:
I would say scavanging is much LESS important on forced-induction engines (same, but different way of saying it). If you look at overlap specs on high-end forced induction cams, the overlap is cut back to less than 5 degrees, compared to about 25-30 on stock N/A cams, and as much as 80+ on performance N/A cams. If you're talking about turbo engines that rev to 10k+, I'll conceed that the intake velocities are reaching the point where scavenging is beginning to work on a forced induction setup as well, but we all know that 99.99% of street driven vehicles will NEVER reach this.
Very true - I admit that sometimes going through the 'theory' behind all this, I'm sometimes late to figure whether it's really a big concern in my powerband or not. ;)

D-Dayve said:
I never spoke about exhaust backpressure being so high that you're stalling the airflow. I stated that if you leave the intake valve open for too long (excessively retarded), when the piston comes back up, it pushes the air back out of the cylinder, and into the intake manifold, causing the INTAKE charge to slow or stall.
I apologize, I didn't mean to make it out as though you did say that - I was only trying to point out that if you are opening your exhaust valve a little on the early side, it should not be a huge problem - your exhaust pressure just aft of the exhaust ports should not be so high as to prevent the exhaust from leaving the cylinder quickly on its own.

D-Dayve said:
The point of forced induction engines is that the boosted intake charge pushes the air in all by itself, not requiring the aid of overlap (in street RPM applications). You're also not losing any intake duration... you're just changing when you're doing it, so you wouldn't lose any measureable amount of potential stroke pulling the intake charge in (because it's being pushed), and you've still got the same fill time in crank rotation degrees.
Quite true - but you can certainly tune the intake and exhaust to give you some scavenging over a narrow power band, giving you (hopefully) more power than the guy racing you ;)

D-Dayve said:
Closing the exhaust valve sooner will cut down the overlap. When getting performance cams of ANY engine, the exhaust will always be the main power getter out of the two (intake vs exhaust). It will NOT dilute the next intake charge because you're using the exhaust charge to draw in the next intake charge (remember scavenging?). You're actually diluting the exhaust charge with intake, and that's what you're aiming to reduce (turbo chill).
What I mean, is if you have too much pressure in the exhaust, the backpressure will keep some of the exhaust from flowing out properly, and dilute the incoming air charge). I meant that statement in regards to having too much backpressure - and in OHV applications, it has been my experience that camshafts that are so called 'blower cams' cover this up by shutting the valve quickly (decreasing overlap)

If you have proper exhaust flow, then you shouldn't have that buildup of exhaust pressure that your engine is working against - proper exhaust flow will let you take advantage of a little extra overlap (nothing like a hugely cammed NA, but along the same lines) for increased scavenging.

D-Dayve said:
Thanks for adding to the thread in a classy, respectful fashion! I welcome all questions and comments, and the occasional respectful arguement as well! :)
Not a problem, I love discussing things like this (and learning more, as always!!)

*edit* One quick thing that many in the OHV world don't understand - LSA (Lobe Seperation Angle) - BIG time proponent on how wide/flat or narrow/peaky your powerband will be. Seems to me that on a DOHC engine, with the exhaust and intake camshafts seperate, you could seriously do some tuning on the LSA side of things.... adjustable cam gears are good there :)

John
 

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Will my Supra ever run?!!
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Discussion Starter #11
Absolutely correct! I only brought this up to point out that what is best for idle isn't always what is best for WOT performance.
I think it's pretty much safe to say that what's best for idle is almost never best for WOT. Performance parts don't usually give you "magical horsepower from nowhere" (unless you're talking about turbos, NOS, superchargers, etc.). When dealing with performance engines, the most crucial thing is to realize where you want your powerband to be. People get wrapped up in this whole WOT, high-hp world, and don't realize that there are people out there who would like bottom end. I've designed and built several high-RPM, high-hp engines, but I've also designed and built some low-RPM torque-monster and commuter engines (my dad's Prelude was one of my commuter torque monster engine guinea pigs).

I think it's very important to point out that modification goals have to be suited to what YOU want, and not what someone else wants, so don't go get the biggest set of cams money can buy if you're trying to drive your car in thick traffic every day.

you can certainly tune the intake and exhaust to give you some scavenging over a narrow power band, giving you (hopefully) more power than the guy racing you ;)
Here's the catch though. Peak vs. overall. Is gaining 4hp for 1000RPM worth losing 2hp over 4000RPM? It all comes back to what the individual's goals are.

What I mean, is if you have too much pressure in the exhaust, the backpressure will keep some of the exhaust from flowing out properly, and dilute the incoming air charge. I meant that statement in regards to having too much backpressure - and in OHV applications, it has been my experience that camshafts that are so called 'blower cams' cover this up by shutting the valve quickly (decreasing overlap)
"Blower cams" are just like any other cams. They keep the exhaust open farther, and for longer. The key is not to leave it open for too long, or if you do, open your intake a little later. It's duration vs. lift. If you don't open it as far, but open it for longer, you can have the same amount of flow as if you open it far, but for a short duration. Cam grinder experience is a good asset to have here. If your grinder has lots of design experience in this area, he'll give you what you want, and not screw it up your application. Remember, you get what you pay for when you have a cam ground!!!

*edit* One quick thing that many in the OHV world don't understand - LSA (Lobe Seperation Angle) - BIG time proponent on how wide/flat or narrow/peaky your powerband will be. Seems to me that on a DOHC engine, with the exhaust and intake camshafts seperate, you could seriously do some tuning on the LSA side of things.... adjustable cam gears are good there :)
That's the main reason why I stopped playing with SOHC engines. I got bored with them... the adjustable cam gear only allow you to retard or advance BOTH intake and exhaust. Not really living up to the term "adjustable". With a SOHC engine, you're pretty much left with whatever the cam grinder decided he could fit onto a cam that would fit in your engine. I got out of SOHCs as soon as I started getting into tuning, and I haven't owned a single cam engine since! It also helps on the N/A-T conversion process.
 

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I think it's very important to point out that modification goals have to be suited to what YOU want, and not what someone else wants, so don't go get the biggest set of cams money can buy if you're trying to drive your car in thick traffic every day.
This statement needs to be said again and again. It is flat truth - YOU must build YOUR car, the way YOU want it.

I started getting heavy into engine building with my first car, a '77 Trans Am - had a Pontiac 400 in there, and it was a low end torque monster. 3.75" stroke will do that for you ;) Then I learned you can actually rev that big beast of a motor, as the 4" bore + loooong freaking rods all stock will let you take that motor up to 7k rpm without much problem (providing good rods + stout valvetrain).

So, cam swap + head swap, and the motor was a radically different beast. Starting learning about dynamic compression ratios, and camshaft tuning - I went through, no lie, about a DOZEN different cams, comparing characteristics of more duration/lower lift, more lift/less duration, various LSAs, and everything.

I had that car anywhere from running 16s stock, to a personal best of 11.4 in the 1/4, till I got rear-ended by a drunk SEMI driver.

I ended up swapping off the Ram Air IV cam grind I was using, and going back to a 224/230 @ .050" - Not having power until 3krpm was getting old, when I just wanted to go cruising. This is also why I got into forced induction ;) My dream car will always be to get my '77 TA back again, with an Indian Adventures II Aluminum Block, and built a twin turbo 428 running EFI.

Anyway, I'm happy to have learned as much as I have, but I've realized that the physics between pushrod vs DOHC are the same - it's just different ways of doing it ;) (part of why I don't get the pushrod/OHC rivalry :1poke: )

For a street motor, I like a wide LSA, minimum overlap, mid-range lift, and decent duration - the BC 220/226 cams + Titan camgears look like they'll fit the bill well for that. What's your opinion on them?

For a drag only motor, it's a different ballgame. Tighten the LSA, increase overlap, and set everything for that 4k-8k range you're going for. Will you make more power than the 'street' motor? Of course.

Will you be nearly as fun to drive on the street? Depends on if you like to keep shifting :)

Either way:

I think it's very important to point out that modification goals have to be suited to what YOU want, and not what someone else wants, so don't go get the biggest set of cams money can buy if you're trying to drive your car in thick traffic every day.
 

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Grumpy Old Man
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A lot of the tech involved in my Car is new to me so I'm still feeling my way with what does and doesn't work in this application!

I'm finding quite a bit of the knowldge I picked up at the race team in the 80's is applicable due to the output I'm starting to make the difference being the sophistication of current tech is making it more user friendly in the real world!

Back then a 500>600rwhp 3.0L car would have had maybe an 800rpm powerband from say 6200>7000 rpm and been a filthy pig to drive.

For me I erred on the side of caution selecting my Cam grind but in hindsight taking my above statements into account I feel I could have gotten away with some more lift/duration and still been able to drive it on the street!

This is what I went for> .351"/9mm lift
280 degrees duration 226 @ 50thou

In the future I'll play around with LSA and see what gains are to be made in drivability as for now I've installed straight up according to the timing tag.

I tend to "believe my own eyes" as often the theory doesn't pan out in the real world but it's good to have a start point and this discussion is interesting!
 

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Will my Supra ever run?!!
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Discussion Starter #16
The price is definitely descent. When I worked as a cam grinder, my boss had spoken with Brian Crower a few times and found him very knowledgeable. He's a descent guy, and has a good reputation. Crower has never released a crap product and had issues (like a good handful of cam companies out there have done). Crower products seem to be well tested and of high quality. I've inspected a set of Crower cams myself, and found them to be very high quality compared to other products I've seen. I'd rank Crower products in the top 10% of the industry as far as quality goes.

As far as specs go, those are three very different, very useable cam profiles that should exhibit very different power characteristics. I would suggest tuning them via adjustable cam gears though. I noticed part way through the thread that the stage 3 profile lopes a bit. If you've read the beginning of this thread, you know what that means. More power is there if you tune the lope out! If BC is making the cams from blank billets, I'm surprised they're not tuned a little better. In the end, you can usually reduce grinding time by a good 20-30% by grinding on center, rather than pre-tuning, so he is probably doing it that way to save the end consumer money on the grinding time.

Personally, I like the "Street grind" best for a DD, but if you tune the lope out of the "Race grind", I'll bet you money that they'll purr like a kitten at idle, and roar like a lion when you step on it. If you have the cash, go with the big ones and pick up a set of adjustable cam gears to tune the lope out!!

Well, I guess this sorta shoots down a chance of me being able to do a GP on cams any time soon :p. I might be able to do something in the relatively near future on regrinds and shims at a cheaper price, but I don't have vendor status right now, so pretend I didn't say that :p.
 

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475RWHP 449TQ and climing
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I have a rebuilt head with comp cams 975-12 springs with an installed height of 1.5" and a 55lb seated pressure, and a bind rate of .950. Would I need to change the new springs that I have to the group buy suggested springs to use the 272 profiled cams. I plan on having a 7250 redline.


Seems like the 272 ex and 264 intakes may be a good combo also.

BTW I have cam gears
 

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Grumpy Old Man
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Personally I wouldn't use a single spring in a performance application Ant....

I would have lost the motor if I hadn't had duals when this happened :(

 

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475RWHP 449TQ and climing
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Personally I wouldn't use a single spring in a performance application Ant....

I would have lost the motor if I hadn't had duals when this happened :(

How did you do that. Are the crower springs single or dual. whats your part number for the ones that you are uing. Also are they drop ins.
 
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