Ain't that the truth.... cool thing is if you do everything correctly you can get them both.

Good posts keep em coming.

 

Hey Rookie, good questions. Bigger cams aren't being a crutch, it's just a way to open the valve quicker, higher and longer. back when I was drag racing the Super stock classes couldn't have ported heads but limited work done within 1/2" of the seat. A good example would be the guys who ran the pontiacs, those heads without porting could at best flow around 240 cfm and would peak flow at approx .550 lift. But they still ran enormous rollar cams in excess of .750 lift with durations @ .050 around 285-290.If they bolted on ported heads I highly doubt the camshaft would be any differant. My theory and I'll stick tight to it is to choose a cam for what you want the motor to do, don't choose the cam to match your heads, it can't be done. the head is only a restricion and the motor is going to pull as much as it can get through that port. if you do cam now and add ported heads later, you wont need anything differant than what you've got. you'll just make more power and probably carry a few more rpm's. And to your first question, NO, I don't work for AFR and never have, I thought my post's made it apparent where I worked. I was at roush for 10 years and I ran his cylinder head R&D for all the V-8 programs including helping them with the IRL team as well, I left Jack at the end of "98" as I saw the writing on the wall that he was within several years going to move his operation down south, Was not gonna do that. I worked for a development co. for couple of years doing mostly R&D for Ford, Harley D. and several race teams. when I was just about to accept a job with Harley in their new devp. faclity I was approached by one of Roush's best engineers that had recently quit and moved to Livernois motorsports when they were just getting started, He wanted me to stay in the area and I really didn't want to move out of state anyway so that's where I've been for the past 4 years

 

Nothing wrong with huge VE, vol eff is a good thing.

BTW it's BSFC, Brake Specific Fuel Consumption.

A cam that is right for a stock cylinder head cross section and flow curve is probably going to be different from a ported head. More cross section you have the less cam you need to do the job.

A cam can help a bad stock casting make power, but it will never make the same power as a cam setup for a ported head in the same RPM range.

Bret

 

Tucanare,

Head guys vs. cam guys here lol.

Yes the cam will fit a RPM range, but changes to the cam will make it have a better TQ curve in the RPM range you are running when it's matched to the head.

IMHO matching a cam to a set of heads can be done.... Then again you port heads and I design valvetrains so it's hard for us to agree on this one.

Bret

 

So can you explain why some cams (while being in the same power range) work better with some heads and not with others?
The reason I'm asking is take AFR's for example, and my Stealth II cam 224/220, .581/.581 116+0. This combo has been run and it was found that although the Stealth being in the same power range as a TR224 or similar, it did not fair very well with them. However with a ported 5.3L with good exhaust flow (like TEA), it was producing much more (20>30 more rwhp). {valve size, SCR and quench being equal}.
Basicaly could you give us your thoughts on how do we determine if the cam we choose fall within the parameters of our heads? without over camming, reverse, equal or standard split or even under- caming.

 

Rrett, Your right, I was the cylinder head guy but I also sat in and watched the cam swap tests and went over the data with them. The one thing I saw for sure is if we found a better cam for the big tracks it was always the best cam for big tracks regardless of the port size, same for the short tracks and the trans/am as well. We made some huge port size changes with t/a as well as the restrictor motors and when we found something with the newer ports we would always run a full matrix of cams through them that had differant qualities but the cam that was our current best still was the cam that ended up the best, The H.P. curve of the cam and the places where it was better or worse was always exactly the same. Maybe because these motors were so efficient and we were always looking for the 2's and 3's that we saw this. I guess it could happen with some motors that have an inefficient design and you have to chase more with street driven cars to get the perfect cam. But in my mind if we went through the same matrix of cams on an LS1 as we did with the cup engines and found the perfect cam for the rpm band I was looking for I would bet my life that it would end up being the same cam if you now ported the heads. I guess what I'm saying is that it doesn't mean that swapping a cam with the ported heads couldn't be better, What I'm saying is that the cam you just replaced was probably not the perfect cam in the first place. How many people or shops could afford to set up and run 50-100 cams with slight variances to mathodicly dial in the motor. I'm sure your customers wouldn't want you making a thousand dyno pulls or could afford it to find that last 20-30 H.P. When you don't have an unlimited budget like a nascar team you pretty much just take a best guess at a cam by the rpm band your looking for, I've never seen in any catalog 2 differant cams for the same h.p. band but 1 is for a stock head and one being for a ported head. With all the cam companys out there you'd think just one of them would have some cams dialed in for this if it was true....I just haven't seen it. Sorry I had to disagree with you. I didn't "just" do porting, I also was in on manifold design and setting up valve train geometry as well

 

Tucunare,

I can understand where you come from on that. A camshaft will have a given RPM range that it works in and yeah you can pull your hair out trying to make something better, hell I have that case with one cam I have done, even gone far enough to litterally beg for a series of lobes to be changed over to a S journal from a R journal at Comp and got a big NO from Billy Godbold. lol They just weren't going to work on a smaller journal, and I didn't wanna pay the coin for the new design with specs like them just to try to find 5hp more on a "stock" motor, just no cost benefit there.

Problem is when we are talking about gains of 75cfm and compression ratio changes of up to 2 points, that dictates different camshafts. I've done some camshafts for guys that run stock heads on a car then switch over to a set of ported heads and that same cam kicks butt there as well too. In this arena the combinations change so much it's crazy, and when you change heads you are most likely changing a lot of other engine specs as well. You could easily turn a tame nice running car on stock heads and compression to a detonating mess when you swap the heads over with a raised compression ratio. I know I push the limits of pump gas more than most race motors push the limits of race fuel, at least if you are talking about NA motors. BTW did you work on the cup motors in the Pre 12:1 rule era? Sounds like you did if you were around in the early days of the plate motors.

The big difference I have seen in street motors vs. race motors is how big of a change a proper camshaft will make to the TQ curve, usually bigger differences than what you see with a change in cylinder heads, and paired up correctly they make huge differences. OTOH when you have a circle track/road race/drag car that has a cam that works in it, a cam change will make a slightly smaller impact. If that cam was PERFECTLY optimized for the car/motor then you ain't gonna do any better.

Issue that's relative here is that guys here don't have a optimized camshaft, even when you consider the large amount of restictions on the cam design due to the fact that it is a street car.

I agree, you are most likely going to get the intake valve events correct and they will be correct for any cylinder head you can put on that motor for the most part. As long as the RPM range and compression ratio stay the same. You can still change the TQ curve matching the right exhaust valve events to the new heads, granted it's not going to be as much as any move you make in the intake events. I've still had setups that had way to much exhaust lobe for them, but when you tried to fix that on the cam you lost power, so yeah even a set exhaust lobe for a given combination can be perfect if you change the setup.

The unfortuneate problem here is that NOBODY is going to do cup style testing on a LS1 for performance reasons. There are probably more chassis dyno pulls done with LS1's every year than engine dyno pulls and there is no way they could even find a repeatable 1-2hp change, so it would be close to chasing your tail here. It's also a setup that's not even close to it's evolution, it's closer to a ape than a human in comparison to a cup motor. Hell everytime we find a change that adds power, nobody comes in to put a kabosh on going any further. i.e. journal sizes, bore limits, component masses etc.... We pretty much have a free range to work on here.

Bret

 

Bret,

Your an engine builder right? Ever spent any time on a dyno? BSAC=Brake specific air consumption. This represents the engines efficiency rating in converting air into power. (Pounds of air to support 1HP for 1 hour.) Most people ignore this value and focus on BSFC. (Pounds of fuel to support 1HP for 1hour.)

FYI, an engine can move a huge amount of air and not make any power. Assuming the tune and everything else is correct, this is usually indicative of too much exhaust flow, or too early an exhaust event. Usually detectable with huge VE numbers, and low power output.

Then again, I'm just a "rookie" and could be way off base here!

 

Rookie,

Never looked at that... I look at the actual CFM going into the motor and Vol Eff rather than the BSAC. That is a good way to measure it though.

I agree that a motor can move a lot of air and not make good power.... it can also be a indication of too many losses in the system as well. Too early of an exhaust event might also says too much LSA on the cam, or too much duration, from what I have seen it means take out that advance on the cam and make the ICL and ECL the same.

Bret

 

Not bad rookie, We would see this all the time when we would run the big volume heads with high lift flow numbers, The air consumption through the bonnet would be way high but the motor was down on power throughout the curve, This would drive Jack nuts. He just couldn't believe that if you made the motor pull in more air fuel that you weren't going to make more H.P.. So he would end up throwing a dozen cams or so at it just to try to prove a theory....uh uh, never worked

 

Now we're talking a little bit more than our original discussion, I was keying in on the volume aspect of it.

 

Tucunare,

At what lift should the flow of a LS1 cylinder head be maximized for the (everyday user/ racer?) As you noted, most stay below .6'' of valve lift.

You mentioned mid-lift flow as being the most crucial.... In your opinion, how would a head that flowed great from .1'' to .4'' and maxed out at .5'' perform....when.... paired up with a camshaft that had max lift of .6''?

 

I think the key is good low and midlift flow coupled with a smaller cross sectional area for high airspeed thru the ports which promotes a LOT of good things to happen (can anyone say AFR 205??). I try my best at getting the big peak numbers as well, but as I said MANY times in the past, I made some consessions to peak flow in the design phase of the AFR 205 which helped my low and midlift flow across the board and I maintained the small cross section in the port which was one of my primary objectives.

This post has been very informative (I'm not just looking for an opportunity to pimp AFR....LOL), but the reality is that alot of what is being spoken about lately in this thread directly relates to our product and helps answer the questions as to why alot of you have seen impressive results, both peak numbers and especially in the area under the curve.

Thanks,
Tony M.

 

Tony,
Just drove my SS home from FM and beginning to get a feel for my new engine w/205. I went with a smaller cam and better heads for emissions and streetability reasons.

 

So then I have an interesting example. I recently did some port work on a set of Ford GT-40p heads for my little 302. I ended up at 146cc intake ports. The AFRs were 165 cc. The valves on the GT-40p were 1.85 intake and 1.45" exhaust. On the AFRs, 1.90 intake and 1.60 exhaust.

Intake
lift (in.) AFR my gt-40p's
.100 60 66
.200 123 129
.300 179 183
.400 229 211
.500 243 207
.600 245 (my cam isnt going *near* 600)

Exhaust
lift (in.) AFR My GT-40p's
.100 52 59
.200 118 112
.300 153 155
.400 178 172
.500 191 177
.600 189 (again, no 600 for me)

Now, why did the 165 make 24 more rwhp ( 329 vs. 305) ?
The AFR 165 made almost exactly the same curve until 5000 rpm (326 lb/ft) and then took off.

One would look at the cross section, the smaller valve size, and the low/mid lift flow, and what you have just said, and think that my GT-40p heads should have been clearly better for my .544" 218/224 Xtreme Energy cam.

I have said before, and I have shown numbers on cam lift angles to show, that .500+ lift on thes heads matters VERY MUCH. Granted, a smaller port that flows the same at 28" may flow quite differently at 100" than a larger port...

I think that by pointing to low-mid lift flow numbers and saying "Look... the power!" is grossly simplifying things to the point of becoming nothing more than a sales tactic.

 

Chris....

As I said it's the right sized port that matters. The ported GT-40 for the most part is too small. Smaller is not always better, especially when you have a head that will run into sonic choke. This statement is the proof that the port was too small "The AFR 165 made almost exactly the same curve until 5000 rpm (326 lb/ft) and then took off."

Given a port of the same size that was HIGHLY engineered to work well at high velocities it might make the same or more power... but the problem is probably the casting itself.

What did happen though is that you made more power per CFM of head flow with the GT40 head. It's more efficent at making power with every CFM you gave it but something else (namely the port size) choked off the ability of the port to make TQ at high RPM.

This is why I said what I said above.... the right size port for the casting at hand and the application is the key. Only thing you can do to change that is have lots more knowledge or money to spend on the knowledge to get the head to work. Then at that point you might as well move to a better casting unless the rules force you to do this.

Bret

 

The conversation evolved man... general statements are general and don't always work. I see your point but you gotta play to the audience as well.

In the case of a stock LS6 casting, a little milling and some porting will get you that 2 points of compression and 75cfm, that's where the problem of a "perfect cam" for a RPM range and cubes doesn't always work. That's all I'm getting at.

Bret

 

Visceral, You've got a lot more going on here than low lift and port size, for one your now talking about nearly 20 cfm at .400 and and 30 cfm @ .500. this trend is also probably starting by .340-.350 lift. While I talk about the importance of low and mid lift flow relative to the cam lift the motor also needs a certain amount of overall airflow to make peak power. I described earlier how we would make that sacrifice on the Road race motors. Another huge thing you've got going on is your ex. valve size. The flow being somewhat close doesn't simulate what's going on in the motor, at lower rpms the motor can get the ex. out fine but then you'll hit an rpm where the throat size is too small and it's like having a potatoe in your ex. pipe. Again we saw this in the Cup motors, We tried a 2.175 int and a 1.55 ex, We made monster gains in Int. airflow, especially down low and it carried the highs as a bonus. On the bench I was able to get the same flow as the 1.600 valve because we were more unschrouded at the bore. the thing is to get that flow the throat had to shrink .050 as well to maintain the proper venturi for airflow. On a flow bench you've got unlimited time for it to reach a peak number but in a motor the higher the rpm you go the faster your trying to push the ex. out and Throat size is very important. When we ran that Combination we started dropping power at 4000 and well before peak we were dowm almost 35 h.p. that was monster losses for us and it sounds exactly like what you saw with your motor in the higher rpms. Your case here is not representitive of the points I was making and people should not use this as a case to back up other theories about port size, Again my statements are not gereral, I'm not simplifying anything, and I've got nothing to sell, I'm just relaying imformation for you do do with as you will. There could of been other factors in your head swap such as port allignment that could of played into it as well, remember in a comparison, "ALL" other things need to be equal, you had a lot going on other than port size

 

Precisely My point was that there are many more factors than a small port and good flow numbers at and below 50% of the cam's max lift. It wasn't you that made that statement.... no worries.

Again, exactly the point, and I wasn't directing my concerns with over-generalizations at *you*.
The AFR LS1 205 is a good head. I have alot of respect for it. BUT... one cannot just point and the smaller port volume and the low/med flow numbers and say "Look! A superior horsepower curve!" like someone other than you was doing. For the $$$ that an AFR 205 costs, set up... you can often have a head well designed to your specific application, built, and assembled from a 5.3, 243, or 317 casting that is just as (or more) condusive to your goals. Unfortunately, I think there is only one or two sponsors that can offer that specialized expertise and reliability. And to the topic of the post... I don't think MTI is one of them. Jayson likes to built really nice cars... great heads extremely specialized to your application is past the point of diminishing returns for him, and there's nothing wrong with that, as long as it's understood.

 

Visceral, no offense taken.