Isn't the cc305 and the hotcam pretty close as far as lift and duration??? Whats the HC's LSA. When we degreed my cc305 the lsa ended up being 112 and had a little extra exhaust duration. Would the tighter lsa make me bleed boost?? Ihave the stock s-trim pullies for 7# and I see anywhere from 10 to 12 with the stock heads and 1.5's.

 

The HC is 218/228 .525 with 1.6's and the CC305 is 220/230 .544 with the same 1.6's. I dont remember what the LSA is on the Hot cam......
Am I getting this, that the general consensis is a blower cam should be more agressive on the exhaust lobe? and have a wide lobe seperation? If so what is the "new idea" that you are trying???

 

Hey mike... You recommend a 224-236 in early posts and then steer people away of hte +12 duration????

I did have a 215/220 cam in my S/C an the car did 393@5200rpm. The car was lots of torque fun bla bla bla... but...

after 5200 it would die like a FREE FALL!!!!!!

I lost 70rwhp from 5200-5600rpm...

I went to the 224/236 cam and the rev range went up, but it didn't fall on its **** after its peak.... I had peak at 5750 and had 20rwhp less at 6200+

So i guess the exhaust choked.. maybe it was because my heads didn't flow all that well on the exhaust, but we will find out... I have my new cam 224/236 116LSA high lift version. Now is the time to change it if the results might be proven.

 

I recommend the 224/236 because it is tried and works reasonably well, but I don't think it's optimal. I haven't tried something different yet, so I'd rather not use someone else as a guinea pig. But. . . if someone is willing to try a little experiment before I get around to it. . .

Rather than looking at the intake duration/exhaust duration, LSA, advance, it is better to look at IVO, IVC, EVO, and EVC. Of course these can be calculated using duration, LSA, and adv, but the timing of actual valve events is what tells the real story of what goes on and why. For instance, generic statements about narrow LSA being bad for superchargers aren't necessarily true unless you calculate actual overlap degrees.

Mike

 

Well.. What do you call optimal?? 5-6rwhp more?

For instance.. I would like to know what do you consider optimal for a 224 tops intake duration and such. I dont want to go beyond that as I dont want to rev it more than 6300-6400 AT MOST. I think that 224 in a 383 gives you a nice rev range for a street car.

I have played a little with EAPro. But it looks like im going to play some more and see what I can come up with, as I prefer to loose $300 right now than having to remove and replace again.

After this .. I hope its DONE!!

 

5hp, 10 hp, 20 hp, who knows? Nobody's tried it yet. I don't even know for a fact that it will make more power.

Your 224 limit on duration is exactly the kind of thing I was referring to earlier. IVC has a large effect on rpm range. IVO has a very small effect on rpm range. So, you can increase duration on the intake without increasing rpm range IF you add it on the IVO side. An example is that a 230 intake lobe on a 108 centerline will make the same low-end as a 224 lobe on a 111 centerline.

Maybe 224/230 is optimal, maybe 224/224, maybe even 224/218. Reverse split cams work very well in LS1's, import cars, street bikes (my ZX-10R cams are 245/225), supercharged imports, and turbocharged cars. Hot Rod magazine printed an article on a 200 mph supercharged Civic who's cams were 250/210. Some dirt-trackers are even starting to use reverse split cams, which goes against all traditional SBC logic.

Can anyone explain why turbo cars run well with reverse split cams? They have even more backpressure than supercharged cars. And don't say that "they need more exhaust velocity to spin the turbo" because that's a load of BS. Velocity around the valve and velocity through the turbine wheel are unrelated.

I built an elaborate spreadsheet that plots piston position, piston velocity, valve position, cylinder pressure, and torque applied to the crank. What I found agrees with David Vizard's SBC camshaft book: supercharged motors retain cylinder pressure later in the power stroke than naturally aspirated. So, you stand to gain more work from this pressure if you delay EVO. This means less duration on the exhaust.

Mike

 

Turbo cars work well with a reverse split cam because of the exhaust back pressure... It closes the valve sooner so there is less chance of contamination of the intake charge and even reversion to the intake.

Its not the same thing as my exhaust... I think I am seeing around 5-6psi back pressure at WOT vs 12-15psi boost that I will be seeing.. Gases will flow forward. On most turbo cars its the other way around... You get 10-12psi boost but have 16-20psi backpressure. So that plays a role.

On the bike issue... I feel that exhaust headers from bikes are even better designed or combined in length and shape than are the LT1 headers and I also feel that the siamese exhaust port and that not all ports are the same has something to do with the E/I being different than in ls1 cars and bikes. I bet that your bike has a very high E/I ratio or maybe even flows better because of the header tunning, unless you are getting the boost of the ramming effect when going up in speed (100+mph). So all that plays a role in why a bike camshaft is very reverse.

I will play with EA Pro and let you know what I find out.

 

So, since turbo cars have more backpressure than boost, you must reduce overlap to prevent exhaust from backing up into the intake? Isn't this the same as a supercharged car, where boost is higher than backpressure, so you should limit overlap just the same?

You can reduce overlap to prevent both scenarios, boost in the exhaust AND exhaust in the boost. This does not mean that you need a reverse split, though, only less overlap.

They use less exhaust duration to take advantage of the pressure remaining in the cylinder later in the power stroke.

Let's compare a good NA cam (GM 847) to an accepted turbo cam of, say, 236/230 - 114, +4. The 847 cam is 234/242 - 112, +6. We'll throw the good ole' supercharger 224/236 - 114, +4 in the mix also.

EVO: NA 59 BBDC, Turbo 53 BBDC, SC 56 BBDC

But I though a boosted motor had more exhaust in the cylinder, so you had to let it out by opening the exhaust early??? Not so. You have more exhaust in the cylinder DOING WORK, so let's keep it there until its done. So, why is the SC cam any different from the turbo cam in this aspect??? That's my point.

EVC+IVO (overlap): NA 14, Turbo 5, SC 2

Much less overlap for the turbo and SC cams, as expected.

IVC: NA 43 ABDC, Turbo 48 ABDC, SC 42 ABDC

This, more than anything else, determines rpm range. I would expect the turbo motor to have a higher rpm peak than NA, all else being equal - which it is not. SC should close intake early to make up for a lack of low rpm boost.

So, let's "fix" the supercharger cam by making EVO 3 degrees later (to match the turbo cam). We'll close the exhaust valve (EVC), say, 5 degrees sooner than the turbo cam since a SC motor has an easier time pushing exhaust out due to lower backpressure. We'll keep overlap the same as the Turbo cam, since it is equally important in both, albeit for different reasons. Let's leave IVC alone since we like the rpm range of the 224/236. What does that give us?

EVO: 53 BBDC
EVC: 3 BTDC
IVO: 8 BTDC
IVC: 42 ABDC

The final spec's are 230/230 - 112.5, +5.5

Any takers?

Mike

 

I will run EAPro now.. give me a sec

 

I get a final spec of 230/236 on that cam according to ea pro
111lsa 4 advance

HP results are

RPM --224--230
5500--820--823
5750--853--854
6000--874--875
6250--878--884
6500--866--885
6750--842--860
7000--798--815

AS you can see... up to 6250... difference is negligeable...

the difference starts to show when the 224 is too small for the 383 at that rev range and the 230 shines over.. .FWIW 230 is too much... Yes it made more power.. but I still prefer the 224 for ym rev range. The other thing is... you changed the instake duration.... it should have been the other way around

 

Look what happens when I put 8 EVO in your cam

it gives me a 241 exhaust duration

RPM --224--230--230/241 cam
5500--820--823--826
5750--853--854--858
6000--874--875--879
6250--878--884--889
6500--866--885--892
6750--842--860--873
7000--798--815--828

See?

a higher and flatter curve... and true, the same thing up to 6250, difference is negligeable. but the more intake duration the more exhaust duration you need.

Im still sold in the +12 duration in the exhaust.. come on mike convince me!! now is my chance to change my cam.

 

Now with your cam.. it was 53 -3

here are the results

RPM --224--230--241--230/230
5500--820--823--826--816
5750--853--854--858--849
6000--874--875--879--869
6250--878--884--889--872
6500--866--885--892--857
6750--842--860--873--842
7000--798--815--828--796

AS you see... according to EAPro... your selection is worse than the 224/236 cam with more intake duration than the 224/236 cam..

See how both the 224/236 and the 230 230 free fall the same way... the difference is that the 224 freefalls for intake as you can see when you put up the intake in the second cam to 230. but your choice falls because of lack of exhaust...

S/C LT1 cars need exhaust is what I believe... Let me know what you think of this...
These are my expected FLYWHEEL HP for the YSi-trim.

 

Too bad we're not racing computer programs. . .

I have no idea what parameters EAPro uses in its calculations. They may only be considering port gas dynamics, compression ratio, etc. . . without looking at the PV curves / Moment curves to see what happens in the cylinder during the power stroke.

I'm not trying to convince anyone else to do this since I don't have hard data saying it works.

My recommendation early in this thread was to use the 224/236 cam.

I'll try a different cam myself and if it works, GREAT! If not, TOO BAD!

Mike

 

Dont get me wrong... we are just debating here.... EApro uses many things to calc its performance....

Its a nice feauture... The reality is that in 800hp 10 go unnoticed... and you will probably up the boost or do other changes than just a cam swap. Unless its a radical change...

I do feel from past experience with my car that the LT1 needs more exhaust specially when supercharging or nitrous....

The LSx doesn't.

Im just here debating because my high lift 224/236 cam is waiting to be installed along with the heads and many other things, so now is the time to discuss cam posibilities and options.

 

If you are going to go through the trouble of swapping cams...why waste your time by going with a Hotcam? Why not get the best cam you can?

Seems kinda obvious to me.