Care to share the spec's of the old and new cams?

 

Yes, I already knew that. You should also know a lot of people aren't going to be as open or very open about the information they collect. Especially with competitors out there. That should be pretty obvious too.

 

I would like to add a few things not brought up yet. We have theory's of boost bleed off and which valve events are better for FI setup's.
Now my question is for the guy's with FI like the Vortech setup's on the F body's.
With a blower that is very small and not capable of pushing much CFM's I belive cam shaft design might be even more critical.
But I have no proof of that. I just feel that with a vortech setup you need to try and get everything as efficient as possible to help that little head unit work.

And the boost is a measurement of restriction saying....
The last Vortech F body we did made 7 psi, when we changed out to a fast 90/90 and a set of ported heads his car made 5psi. More HP? Yes but less boost.
We took the restriction's away and less boost was "read" on the boost guage. More air was geting into the motor however and the proof of that was the additional HP, and the fact that the tune required more fuel to get the car back to the same A/F ratio.

 

Let me also add that we all have oponion on what works best.
If you look at different FI setup and try and compair one setup to the next it is tough.
However on this board alone I have seen a huge number of different guys that have boosted cam setup's. Many have different cam's. Not once have I seen a cam go in and the car loose power over stock. There are even a few guys running G5X2 and G5X3 cams in their FI setup's. Is it the best cam for that setup? Probally not, but does it work? Yes. It clearly makes more power then a similar setup with a stock cam.
Remember like 3-4 years ago and still today when people say that a 114+LSA cam with a 4 or more degree split in duration is a "nitrous cam"
then a guy comes in with a TR 230/224 on a 112 that makes 400 NA and 545 on a 150 shot. We can argue what we believe all day, but the proof is in the results.
I for one don't believe that if your spraying a 150 shot the cam is real improtant, and also feel that if your making power with a blower and any cam then the cam must work no matter who says it won't.

 

From stock to 224/232-581/595.

 

It all comes back to what kind of motor you have or how you want to use it. Overlap does work for FI. Look at the import cars. When they're doing high rpms, they're using buttloads of overlap. Then, when they're driving around town they change to their primary lobes, and now the overlap decreased. With pushrod engines, you don't have that luxury to change profiles(unless they come up with something better than the L92), so you're fixed to one profile, and that leads to fixed power band. It's either low, mid, or high. Your choice. With a high overlap cam, you might be bleeding down low with FI, but when that sucker starts revving up, it's really going to pull. Again, it's to a point. You don't want a ginormous amount of overlap to make your motor rev 10K+, you just want enough for whatever you want your powerband to be, even if it is 10k(good luck with that one in the streets, unless you have nascar money).

I say screw the overlap and go for a later IVC, that way you'll pass smog easier and rev high, especially with positive displacement FI. Sounds almost like a MILLER cycle, if you choose to have a longer intake duration than your exhaust. I think IVC is the biggest factor for rpm. I could be wrong.

 

Precisely.

 

Turbo and Blower cams are TWO DIFFERENT WORLDS IN TERMS OF OVERLAP the results CAN'T be transfered from one to another.

;-)

Bret

 

Flow is induced by a pressure difference. Do you think that 12psi of boost is greater than the exhaust pressure?

I think the arguement here has missed a few key points that would determine what type of cam would work best in a setup. Those would be exhaust/intake pressure at valve events, residual gas, and compression ratio. IMHO there are some situations where a "moderate to big" cam would work better than a tight cam and vice-versa.

 

Bump...

SO how many people have tried some cams with more overlap ??? or tighter LSA's in a blower application ?

From reading the Aussie LS1 site, some of their top guys would suggest cams around the 230/240 with LSA's of 110 and tighter can work exceptionally well in a high power build.

Why would the thinking be so different on each continent ?

 

I have done a fare bit of camshaft testing on differant types of F/I over the years and found, as has been somewhat stated here, that differant types of F/I require differant camshaft designs. I have personally used camshafts from 112 to 121 LSA depending on the requirement, we recently used a 118 LSA cam on a 6.5 litre Twin turbo LS2 that made 760rwhp (aussie dyno dynamics dyno) on 14.8psi and pump fuel with only 16 degrees of timing (far from being maxed out), the car drove like a stocker, got awesome gas mileage and passed an engineering test for legality with 238 degrees at 0.050 on the exhaust! We would have tuned it up more if we could keep the heads on, (L92 for interest sake) and with a LSA like that you might think massive revs, however it made that under 6500 rpm.

Other testing has been based around Twin screw blown LS engines, you can have two camshafts with 114 LSA and have two completly differant results in power, the fact is a camshaft designed for NA use is probably not going to work great in a PD blown engine, the converse is true with Centrifugal however...

So, it aint an easy bang it and go from there, my suggestion would be to buy a tried and proven cam of one of the vendors that has the runs on the board, or go small, you cannot go wrong.

Matt.

 

Agreed with Matt.... I've used some forced induction cams with LSA's down in the range of what you would see on a circle track car.

Bret

 

This thread has some great info! I'm surprized there isn't more actual examples of people trying two cams, one with a good amount of overlap and one with less to none. I'm not going to change my N/A set-up untill I see what it does with the supercharger on. I'm not near as experienced as some of you but it seems to me it can't hurt to try. The way I see it, with a supercharged engine overlap can't make that much difference in power. I can see why it may make less boost but I think the power would be comparable. My example: my car makes 408rwhp n/a with a F14 232/234 112lsa. I'm going to add a supercharger and plan to have around 8 psi. Let's say it makes 600rwhp. Now I change out the cam with one with a lot less overlap. I now get 10 psi but still make the same 600rwhp due to the new cam making less power before the boost. Is this not reasonable thinking? It will be much easier to debate once the supercharger goes on but unless I make a considerable amount less hp then my goal of 600, I see no reason to change the cam.

 

Three points...

1) Lift is not something that most folks should belabor in threads like these, because most folks are not running combos that would merit going over 600 lift anyway. If you are building a beast of a car with heads that flow 350 at 650 lift well you are probably getting great advice already on cam selection (one would hope). If not, you can do some research. If you are running some good heads like say AFR 225's, your cam guy would want to look at the lift numbers before spec'ing a cam. If for example they hit 325cfm at 625, that's great, but if they hit 320 at 600 and then don't pick up much from ther, most cam guys will just grind a 600 lift cam since they won't necessarily advocate a higher lift cam that might be (a) less stable and (b) require changing the springs much more often. I've run as much as 630 lift with the blower, but am currently running around 600 lift.

2) Andereck's comments mirror others I have seen by Intmd8 and some other guys who do a lot of tuning, that overlap is important. I ran a 236/246//114 cam with my YSi and my power curve was straight across, which was the goal. Guys that race competitively in NMRA running blower will always run at least a 10 degree split and sometimes a bit more, though perhaps the amount of intake duration that they run is also reflective of other restrictions in their combinations. My combo went 9.40@143 at close to 3500 raceweight, and the next fastest similar combo went 9.25@145 or so but he's almost 250 lbs lighter than me. That's telling me my combo was making some good power. I dynoed 680rwhp a week before I went 144mph in July of that year.

3) My turbo combo is 10 times more soggy down low than my blower setup. My blower setup was like a 600 cubic inch n/a setup. My turbo setup feels like an Evo I test drove a few years ago, nothing down low but would push you back in your seat at 4000 rpms.

Bret, posting in a thread, and then 10 posts later saying you won't share data does not work well on message boards, maybe you should not even post. The whole point of message boards from a user standpoint is to do research and interact with a large community of fellow enthusiasts. And I agree with EngineerMike (gasp) about making comments personal, there is no need this is tech site.

Andereck, I'm running a 234/234//113.5 or 114 camshaft, what do you think of that with my turbo setup?

 

John, sorry for not replying sooner. The fact is I just don't know. I don't feel qualified to evaluate your cam choice because I just don't have any experience with turbocharged engine combinations and their special requirements due to exhaust backpressure.

My feeling is that a turbocharged engine will not benifit from positive intake pressure scavenging due to the exhaust pressure being as high or higher under boost conditions negating flow in the right direction. This doesn't mean that some overlap would hurt however. Under light or partial throttle some overlap will help with cylinder fill, even with a log manifold.....I think.

I would probably set the intake c/l around 107-108 for good bottom end and midrange when you're not on the pipe. No reason the car has to be sluggish off boost.
With the basic numbers you've given I think it would be hard to get into trouble regardless of what you do. I do however think most cams of that nature will call for a later intake c/l than what feels right to me.

Take it for what its worth, as I said I'm not comfortable in that area.

 

I'm bringing this post back up because it's the most recent on this highly debateable subject. For guys like me who search and then read through all of these posts in hopes of getting a better idea of what would work with our combinations this thread is still open for business.

After I read this I did some searching on Comp's article list for any relavent testing of a supercharged engine with camshafts of different overlap and found a decent one. It supports EngineerMike's position quite well. On a BBC with a large traditional roots blower with relatively low boost running more overlap overscavenged the heck out of the cylinders down low but once the engine was screaming gained significant power. My conclusion of this particular instance would be your overlap on a positive displacement engine should reflect your purpose for it. On a street engine keep the overlap small but for all out race you can improve top end with more overlap. Remember, you can't drive a dyno.

Here's the link to the article:
http://compcams.com/Community/Articl...?ID=-749654412

Vernon