I figured this would make a good advance tech thread. This is my first time posting a new thread in here, even though I have fun reading around in here on a regular basis. Anyway, on with the question.

I know that one of the most important aspects for making the most power on a given combination, has to do with matching the cam to the head flow. Of course there's MANY other factors that need to be matched as well, but I would like to focus this on the relationship between cam specs and head flow.

Suppose we have the following hypothetical situation and we need to select a matching cam:
Let's say that you were given two sets of heads. One is a set that was ported by your local head porter, who all the locals swear is the greatest head porter to ever grace the planet. We will call these heads, (A). The flow numbers from this set are as follows:
Lift..........CFM I/E
.200 ........... 123 / 102
.300 ........... 168 / 135
.400 ........... 224 / 161
.500 ........... 271 / 185
.600 ........... 263 / 180
.700 ........... 258 / 177

The other set of heads are from one of the well known head porters for the LT1 or LS1 world. We will call these heads, (B). The flow numbers from these heads are as follows:
Lift.........CFM I/E
.200 ........... 140 / 106
.300 ........... 204 / 152
.400 ........... 256 / 183
.500 ........... 282 / 201
.600 ........... 287 / 212
.700 ........... 294 / 219

As far as details on the application go, let's assume the vehicle must idle under 1200rpm, must be a hydraulic cam, and the shortblock must retain NEAR stock cubic inches.
-------------------------------------------------

Okay, I had typed out an explanation of my thoughts on this subject, but I ended up confusing myself trying to rationalize it all. So if anyone can set me straight here, I'd appreciate it.

 

This gets talked about here a lot. You might want to look at this thread http://web.camaross.com/forums/showt...5&pagenumber=1

I posted this there. It really doesn't address heads as such, but maybe it will give you some ideas. Intake runner volume is an important head chracteristic in choosing a cam. If I have the energy tomorrow maybe I will expound on the topic. In the meantime, here's that other post.

I will now go out on a limb and put my "LT1 Cam Selection Ideas" out for criticism/comment. Enough of vague talk, here's "how to do it".

You don't want any of the valve events too late or too early, but just right. Did you ever drive a car with a race cam on the street (or even in the pits)? You wouldn't like it. There is no black magic here. Keep in mind, people have been experimenting with cams in NA SBC's for many years. It is well known what is too much cam, to narrow or too wide an LSA, etc. Stick with what works, unless you have the time and $$$ to experiment.

Here's the story on valve events.

IVC: most important 'cause it determines DCR.
EVC/IVO: important because of their effect on overlap.
EVO: least important (but not unimportant).

How to pick a cam for a HR NA LT1:

1. Chose IVC based on desired DCR. Aim for ~8.5-9:1 depending on what fuel is available, etc.

2. Decide how much overlap is needed based on the intended use. Rules of thumb for a NA SBC based on advertised duration for hydraulic roller cams:

Daily driver: ~50-60 degrees
High performance street: ~70-80 degrees
Race car, occasional street use: ~90 degrees or more

3. Chose an intake duration based on head flow and desired rpm range. Better heads need less intake duration to make hp and the converse. You can't compensate for poor heads with more intake duration beyond a point. Excessive duration will kill low end torque. In general, think of 270 degrees as "small" and 300 degrees as "large". Bigger motors can use more duration. Here are general guidelines for what constitutes a small, medium, or large intake lobe at 0.050" (correlate with the advertised durations above):

Small: 210-220 degrees at 0.050"
Intermediate: 220-230 degrees at 0.050"
Large: >230 degrees at 0.050"

4. Chose an LCA based on the following.

350 stock heads ~114
350 good heads ~112
stroker, good heads 108-110

5. Chose an exhaust duration based on exhaust flow and intake duration. If your heads have killer exhaust flow and a good exhaust system, exhaust and intake duration shuld be the same. Most LT1's need at least a couple of degrees more exhaust than intake duration.

Intake center line: not enought time to go into it now. Usually, 4 degrees of advance is good, which means on an LT1 that the cam is ground with an ICL 4 degrees less than the LSA.

Lift: get as much lift as you can "afford" within the limits of HR technology. More lift = more spring = more stress on the valve train = need for better parts = more $$$. Rule of thumb: limit lift on a street HR to ~0.600". If it's not a street car, use a SR.

Voila - you have a cam.

Note: much of this does not apply to blower or N2O optimized cams. N2O cams follow the above pretty well except that they need a lot more exhaust duration. Blower cars are quite different. The need more exhaust duration and less overlap as well as a later IVC point, depending upon the static CR and fuel used, etc.

Nits, picks?

Rich Krause

 

Rich, you say get as much lift as you can. At what point would this be negated, or where is the point of diminishing results. You always hear, "once to peak and twice through mid lift", so how would more always be better. Also, if your heads flow a peak of 215 @ 500, like a stock LT1, would it be beneficial to go much more than that? I always thought the lift was the reason people say a CC306 is "too much for stock heads". If its just the duration, why not make a stock or close to stock duration cam that has a good bit more lift (within reason), for more power? I know there is power in duration, as there are some stock classes that mandate stock lift cams and they simply turn high rpms for power (i thought). Is there simply not as much power in lift, compared to duration?

 

Hmmm.... Interesting question for Rich, I still want to hear his side, but here is my little tid bit.


This is what I got thinking about in this whole context.

"why not make a stock or close to stock duration cam that has a good bit more lift (within reason), for more power?"

1.6's with a ZZ3/4 cam is pretty close to this, funny thing is that a 2002-3 LS6 cam is too. 208/211 for the ZZ3/4 and 204/218 for the ZO6 cam. There are alot of things too all of this, where the peak is relationship to runner sizes etc..

"I know there is power in duration, as there are some stock classes that mandate stock lift cams and they simply turn high rpms for power (i thought)."

Yep something like Cheap Street at .485 lift. A valve job in the head rules is super important here. Think of it as the lobe area, there are two ways to gain lobe area, lift and duration. Lift is limited by rules, and usefull spring life. Duration is limited by what the driver would consider driveable, and the RPM range. That is a simple explination.


"Is there simply not as much power in lift, compared to duration?"

There is not as much RPM. On a side note it's not the only thing. I occasionally think about the engine I would put in my car, as a engine builder your drive to work or time playing with something in a mindless manner give you times to think about this. The problem is that any engine builder goes all out or doesn't do it. We can't have a half *** engine in our rides, it's stock or unreal so our plans for our own engines get to be a little silly. Now on to the relevant part. My SS needs a LS1, but I don't want stupid amounts of TQ or piston speed that a stroker would give me. Neither do I feel that a re-sleaved LS1 block is a street engine, nor do I want to pay for a C5R block. I'd like some RPM to make HP, stock cubes to keep it cost effective, but retain decent mileage, the most important thing is that I want it to drive along smoothely no I'll effects accelerating from 45 to 65 in 6th gear. So how do you do all of that....... here is where it works with your question. Say I stick with a small cam such as the ZO6 cam, add some rocker arm to it, say a 1.85:1 rocker to achive .600 lift. That solves the driveabilty problem because I have tons of idle vaccum and low duration for low rpm situations, gives me tons of TQ but limits the RPM range, but only with stock sized heads and intake manifold. If I get a slightly larger intake port that flows a unreal amount of air, a intake manifold to optimize the upper rpm band, but not kill the lower band and flow awesome. I could in fact make it all work out. While I slowly gather parts for my engine, this is going to be my little experiment. Basically a unreal HP sleeper LS1 that I can drive to work. It's not your average setup, but engine builders think about the ultimate engine all the time.

So anyways, less duration is going to make less power, but say throwing 20 deg of duration at something if it's done right may not help you out all that much. Sizing the intake manifold, and getting the right cylinder head will get you much closer. On the other hand, that is hard and expensive to do so a regular intake, well ported heads and a little more duration will get you to the HP goal in a much easier manner, especially with a good starting ground like a LS1.

Bret

 

FWIW, I would have both heads checked on the same bench and compare the #'s. Some of the "big name" LS1/LT1 porters supply flow #'s that do not always jive with the flowbenchea that most people use. It is ALWAYS a good idea to re-flow heads to 'confirm" #'s. Some flow benches read high, some read low, some people lie about flow #'s. These are 3 GOOD reasons to re check flow #'s.

I am assuming these are both LS1 flow #'s?

The LS1 is a "special" head and I have seen flow #'s change DRASTICLY from a valve job and a little shortside work so I am not doubting the 2 sets of flow #'s. If person A has not had several R&D hours with LS1's, those #'s could be accurate.

If person B had those heads heads flowed on the same bench as A, the #'s might be closer, maybe not. Selling LS1 portjobs is ALL about claiming high CFM #'s and no body re checks these #'s so they just accept that the #'s are accurate. They USUALLY are not. MTI seems to be the only place that I have flowed their heads and they match up with my bench. I have not flowed Car Teach heads but SEVERAL other LS1 shops are about 20 CFM high on their flow #'s.

You could do a search or post a question on that brands flow #'s on LS1.com. You probably need to ask "does anyone have ACTUAL flow #'s for ______ heads?" or just ask some other porters if they have flowed them.

NightTrain66

 

A good discussion, but to make sense of comparing cam specs you have to set some limits. That's why I framed my somewhat provocative post in terms of an LT1 and meant to say (or at least imply) streetable hydraulic roller cams. After all, a non-streetable HR is contradiction in terms. If it's not going to be streetable, ditch the HR cam and go SR! SR is a better route altogether when talking really hi-po. But that's my point - without limiting the dioscussion it can become very unfocused.

So, on to lift v. duration. My point about lift was in the context of street LT1 HR cams (and the same principles will apply to an LS1 with slightly different particulars). Look at the CC306 as a benchmark. It has 230/244 duration at 0.050" with 0.510/.540" lift (1.5). This cam makes less hp than than a cam using the CC XE #3192/3196 combo. The latter is a 224/236 with .567/.585" lift. So it's "one size" smaller but makes more hp (and torque) and produces more vacuum. I have seen this cam swap done with no other change and it works as I described.

Why? More "area under the curve". Saying "more lift" is quite similar to saying "more area under the curve" and that was my point. This principle works even if the max valve lift exceeds the heads "choke point", though the proportional gains will be all the greater if the choke point hasn't yet been reached. This is because for a given adv duration, a higher lift cam with steeper lobes will have more duration at the intermediate lift points (i.e. more area under the lift curve).

Of course, the CC306 will make MORE hp than the #3192/3196 cam if the rest of the combo is set up for very high rpm. I think that was one of Bret's points. If the rest of the combo is right, and this would include large intake runners, supporting components like springs, retainers, pushrods as well as the bottom end (to include a higher static CR to compensate for the overlap as well as support for high rpm with light pistons, long rods, etc.) then "long duration" will trump "high lift". The high lift will be rpm limited sooner than the long duration cam. And well all know that rpm's make hp (if everything else is right).

So, did I contradict myself? I don't think so. It's an illustration of TINSTAAFL (there is no such thing as a free lunch). This is a basic fact of cam design. Unless you change the paradigm (go to SR from HR) when you gain one thing, you lose another. I still think "lift makes more hp than duration" is valid, in context of a typical HR streetable combo. Anyway, I was just trying to be provocative but also to try to give some guidelines for navigating the slippery slope of cam selection.

Here's some more provocative statements. Again, I am talking street HR cams.

What's "wrong" with most NA performance cams: too wide an LSA, not enough lift, too much duration.

What's wrong with most SC cams: too narrow an LSA, not enough lift, too little exhaust duration relative to intake.

Rich Krause

 

Rich, thanks for the link, that was a good read. (Also, I put a HR, idle RPM, and cubic inch limitation in the original thread )

I have a couple questions about some things you mentioned though.
Just to make sure I have things correct in my head, I thought that advancing a cam raised the numerical value of the LSA? So if you had a cam with an LSA of 108, ground with 4 degree's advance, you would have a cam that acted like it has a 112 LSA?

Brain, here's my take on the CC306 being to much for stock heads. Since a stock LT1 casting, as you mentioned, flows around 215cfm @ .500 lift, the CC306 has enough lift and duration that it holds the valve open at a higher lift than what is optimum for a pretty long period of time. Since the majority of the lift cycle is above the peak lift flow of the heads, it's just not an ideal cam for stock heads.

Bret, the cam you're talking about sounds similar to the setup I'm running now. I've got a new cam that Thunder Racing recently released that they refer to as their "Old Man Cam," or "Sleeper Cam." It features a 214/220 duration with .600/.527 lift. If you would like any details on it, feel free to PM me. I'd rather this thread not turn into a big discussion about my cam.

NighTrain, this is a hypothetical situation, so we're assuming that these are ACTUAL head flow #'s. Not advertised. So you can also assume that they were flowed on the same bench if it makes you more comfortable. And when I originally posted this thread, yes the flow numbers were dreamed up LS1 head flow numbers.


The direction I was hoping this thread would go is kind of veering in a little different direction here. There's hundreds of cam tech threads on here, but I don't think I've ever seen a thread where there was specific relation between cam specs and head flow numbers. Is this is really a simple concept I'm making too hard here? Do you simply find a cam with a lift that matches the heads peak flow number, and use as much duration as you can be comfortable with? Same type of thing with the LSA (per the other thread)?

 

Hmmm

Two things I need to respond too.

"Of course, the CC306 will make MORE hp than the #3192/3196 cam if the rest of the combo is set up for very high rpm. I think that was one of Bret's points. If the rest of the combo is right, and this would include large intake runners, supporting components like springs, retainers, pushrods as well as the bottom end (to include a higher static CR to compensate for the overlap as well as support for high rpm with light pistons, long rods, etc.) then "long duration" will trump "high lift". The high lift will be rpm limited sooner than the long duration cam. And well all know that rpm's make hp (if everything else is right)."

I ment that the opposite way actually. Well kind of. A engine system will have certain traits. If the cylinder head port size and intake manifold runner length are set up to make power at a certain spot then the cam has less effect on the HP than it does on the TQ curve below HP peak. With more cam you could lose 50 ft lbs of TQ in the mid range and still have roughly the same HP (within 5-10hp, which in a 600hp engine is less than 1-2%)

Now duration is something at points that is hard to overcome. The air only has so much time to get flowing into the cylinder and the longer the window for that the higher the RPM band that it can run in. It will usually have less low rpm power because it then has too much valve window and have a low VE there.

Alot of this has to do with the flow curve too, one like you mentioned having less average flow at about any max lift level is going to get it's but kicked. A head with a flow curve that peaks high and is about a strait line rather than a curve with a fat mid section is going to like more lift. So this does play into it. What Rich has said about the relationships of a cam and a port in terms of lift level is true, you are looking at getting the most flow even if you go over the stall point on a bad head. Basically a good head will make more power and the same cam would be optimum on both.

Now area under the curve or lobe area depends on the application how you want to achive that lobe area. Some applications like more duration for their lobe area and some like less. Some situations like a SR with lash need more duration to get the same lobe area. The same duration numbers on a Solid Roller vs a Hyd Roller with the same lift will yield a smaller effective lobe area on the Solid, but most times it want will give you more lift. Solid Rollers since they are for RPM should be over 230 degs of duration anyways, so those disrepencies between the 224 SR lift and the 224 HR (3192) will be there, the 319X series lobes are for bad *** HR motors, which are sub 6500rpm motors.

"Bret, the cam you're talking about sounds similar to the setup I'm running now. I've got a new cam that Thunder Racing recently released that they refer to as their "Old Man Cam," or "Sleeper Cam." It features a 214/220 duration with .600/.527 lift. If you would like any details on it, feel free to PM me. I'd rather this thread not turn into a big discussion about my cam."

The Old Man Cam is a interesting cam. I'd rather run a cheaper stock GM peice with more rocker arm to save the lifters since the 214 is actually a 3190 Comp Lobe. Hence my Old Man cam is a LS6 cam. Which I recomended to my father for his vette.

To address this topic some more. Camshafts in a system that is close to optimum, will allow you to run whatever you want to get the drivng characteristics you are looking for and keep about the same HP level, which in a street car is really what you want. The farther away from optimum (in port size and intake manifold) you will see more gains with more cam. In something like a Engine Masters engine where everything is optimized for a range then there is a cam that is perfect and little changes in it can loose average power dramatically, maybe not peak but average. I know that seems contradictory. When I build a street engine I look at alot of stuff and take tradeoffs, the Engine Masters stuff only has one goal, max average power, so a drop of 10 average is a huge amount to me. In a street car you would never feel that. BTW when I talk more cam I mean more duration with roughly more lift too. The hardest thing to do in cam design is to get more lift in less duration, it's hard to do and is hard on some parts, lifters mostly.

Bret

 

Just to make sure I have things correct in my head, I thought that advancing a cam raised the numerical value of the LSA? So if you had a cam with an LSA of 108, ground with 4 degree's advance, you would have a cam that acted like it has a 112 LSA?


Nope.....

LSA is the first thing you have to look at. A 112 LSA means that both the ICL and the ECL are at 112. When you advance it you take that number say 4 degs from the intake and add it to the exhaust. So 108 ICL and 116 ECL. Which should make it act TQ curve wise like a lower LSA cam, but still idle like a 112 LSA cam. Opposite is true for retard.

Bret

 

Bret, as usual has some useful information.

Just to try to get back to the original question for a second. As before, I will be specific so as to give people something concrete to dispute or support.

1. We have dealt with lift as relates to heads. More lift is better even if the max lift exceeds the point at which the head "stalls". Obviously, lift has tradeoffs, which we don't need to list for this crowd.

2. Steeper is better no matter what the head flows, also with tradeoffs.

3. Intake runner size is the biggie when you are trying to match heads and cam. If you have huge intake ports, you better have a big cam and the rest of the parts needed for high rpm use, 'cause that's where your heads will shine. Smaller ports need smaller cams. A mismatch makes a crappy running combo. Rules of thumb for the LT1 are as follows.

Stock ports can be considered "small". I never measured them, but I remember that they are ~170cc. Do not use a big cam, it won't work well. Stick with intake durations of less than 220 degrees at 0.050".

Ports in the "medium" 190cc-200cc range are ideal for high performance street use. Cams in the 215-230 degree range should work well and oughta be good for up to 6,300-6,500rpm or so.

Ports over 200c should be considered "large". I wouldn't bother with an HR cam for this type of head. It will want to rev past 6,500rpm and need big lift and duration. Figure 230+ degrees at 0.050".

4. The relationship of I/E flow is important in picking a cam. Pick you intake duration according to the rpm range you want. Pick your exhaust duration to go along with the size of the intake lobe taking into account the I/E ratio. Most LTx heads are in the 75% range, less than ideal. That's why almost all LTx cams are "split pattern". They need to be to make up for the exhaust flow of the heads, as well as the restriction imposed by the design of the exhaust sytem (ie no duals, in general). The better your I/E ratio, the less exhaust duration you need.

That's the best I can do on short notice for the question about matching the heads and cam.

Rich Krause

 

Generally this is true. It all depends upon what you consider big ports. I'm not totally from the school where big ports area bad thing, and obviously small cams are a favortie of mine. My thoughts are that there is an inverse relationship between port size/ cam duration"size" in a quality setup. By "quality" I mean excellent flow. So a Large port, say 220cc on a 355 with a small cam will give you some awesome TQ and power. True some people feel that a small cam will waste these heads, Alot of lift small duration and good flow make a lower RPM TQ monster. One way to get high ft/lbs per cube is this combo. The best way to do that is with a high lift, low duration setup. A 204 @ .050 with almost .600 of lift would make a very interesting setup with the right heads.

Quote:

Stock ports can be considered "small". I never measured them, but I remember that they are ~170cc. Do not use a big cam, it won't work well. Stick with intake durations of less than 220 degrees at 0.050".

In my thoughts tradtionaly this is what happend. years ago, guys had 185cc ports with extremely large cams to make power. Even a well ported "fuelie" head back in the day with a typeical solid flat tappet cam would be a 245/255 cam with .500 max lift. That is the only way to make power with such a small port, is make it breathe above where it wants too.

Quote:

Ports in the "medium" 190cc-200cc range are ideal for high performance street use. Cams in the 215-230 degree range should work well and oughta be good for up to 6,300-6,500rpm or so.

Ports over 200c should be considered "large". I wouldn't bother with an HR cam for this type of head. It will want to rev past 6,500rpm and need big lift and duration. Figure 230+ degrees at 0.050".

This might seem odd but a 215cc port if it flows well say 290-300cfm is not too big even on a 350 if you put the right cam to it. With me that would be a 214/224 cam. I've done it, and it works awsome NA. I would agree that a high lift HR would be the way to go in this manner. One thing you gotta remeber is that too high of a velocty will kill HP faster than a small cam will. Especailly if you have the right manifold for the situation, adding tuning pressure to the equation. Let alone what happens to a engine when things like alcohol, Nitro, N2O, etc are added. A 1:2 or a 4:1 air fuel ratio is there (Nitro and Alcohol) you have to compensate for the added stuff going down the port with port size. A NA engine needs the least port size of any engine desing because it is pulling the least amount of stuff donw the port. If you push more down the port you need more area also.

Quote:

4. The relationship of I/E flow is important in picking a cam. Pick you intake duration according to the rpm range you want. Pick your exhaust duration to go along with the size of the intake lobe taking into account the I/E ratio. Most LTx heads are in the 75% range, less than ideal. That's why almost all LTx cams are "split pattern". They need to be to make up for the exhaust flow of the heads, as well as the restriction imposed by the design of the exhaust sytem (ie no duals, in general). The better your I/E ratio, the less exhaust duration you need.

Right on. Small Block Chevy heads in general are always have a bad I/E ratio. So a split duration cam is the way to go. It's all based off of the 23deg design.

Hmmm that's all I have. Not to bust your ***** Rich, your're dead nuts on alot of things somethings I have stuff I think is different.

Bret

 

Bret: your concept of big heads/small high lift cam makes sense in theory. But for it to be sucessful, don't the heads need to big and right, not just big? I have driven a lot of cars on the street with "big" heads and found it less than enjoyable. I'd guess the porting wasn't done properly and the port velocity was poor at low rpm. Is that what's going on with these? Head porting is black magic to me.

I am not so sure about one of your points though. A street forced induction setup can get away with relatively small ports and avoid the problems potentially associated with low end operation and big heads. Yes, you are giving up peak hp. But you can afford to with boost. My combo last year made 597rwhp (without the nitrous) on pump gas with heads that flowed 260cfm at 0.600". With the small ports, it drove like stock with excellent low end torque and throttle response. There was 400ft.lbs at the rear wheels as low as 2,800rpm. Disadvantages? Sure, there's always tradeoffs. It probably would have made more hp with larger ports (though with the blower maxed out, not much I would guess) and maybe it wouldn't have been all over by 6,000rpm, as it was with the small ports.

Anyway, I am putting my theory to the test. This year I have a bigger blower. I had the exhaust ports worked over and they now flow 20% better than last year, with an E/I of 80% vs. last years 74%. I left the intakes alone other than a valve job which netted a bit better low and mid lift flow. So, we shall see how it works with the bigger blower, bigger cam, and "small" intake ports. I want my low speed torque and drivability!

Anyway, I don't feel my ***** are being busted. I have tried to make some specific, though deliberately dogmatic assertions in the hope of generating exactly this kind of discussion. I still hold to the idea that there are a lot of cars out there with intake ports that seriously hamper their usability on the street though. Combine them with a long duration cam and you get a really unpleasant car.

Rich Krause

 

Great discussion guys, I'm learning a lot here.

Something I'm curious about though, is the potential for turbulence with a high flowing head coupled along with a small cam. If you take a head that flows the aforementioned 290 or 300cfm at a given lift, yet the cam doesn't keep open the intake valve long enough (or the head port design just won't allow it) to let all that air flow in, would the restriction cause any kind of turbulence within that intake runner? And if it does, would it be enough of a factor to cost more HP than what is gained with the aftermarket port job?

I guess all of that could go back to having a perfectly matched setup, but I'm still curious about your thoughts on it.

 

Rich,

On a street blower application there is some power with larger ports, but it's not going to hurt you much to have smaller ones.

"I still hold to the idea that there are a lot of cars out there with intake ports that seriously hamper their usability on the street though. Combine them with a long duration cam and you get a really unpleasant car."

True both of these things are not going to work very well unless it is done right.

Two things,

One wouldn't you rather have more flow than more cam? I would since there are more gains from good heads then there are from the right cam. So allowing a bigger port that flows much more, (which we get that a 10% increase in size and a 15% increase in flow will increase the port velocity) and not adding cam you will have a still driveable engine with much more power.

Two, LS1's. Start out in a big volume range from your points. 200cc Stock for a LS1, 5.3L casting and 210cc for a 6.0L and LS6 casting. Now ported for a 5.7L they can be anywhere from 208-225cc. There is a little more to this yes, the port averages about 1/8 longer in length so that eats up a little volume, but not much. One reason they work so well is the head flow. On top of that a big cam for one of those things now is a 230 duration cam. 300cfm out of a LS1 casting and 350cfm out of a LS6 casting, yeah the ports might be a little big but with a nice cam say a 224/224 thye will still be streetable, but have unreal NA HP.

I guess we come from two ends of this. I'm a NA and LS1 guy and you a LT1 Blower guy. I get where you are coming from. I also get how you want low speed driveablity, so do I. My LS1 will have to pull from 40mph to 65mph in 6th gear everyday on my way to work, thinking about that and how you do that in the engine design and still have tons of power is fun, but ulitimately makes one fast sleeper.

Bret

 

Bret- If you wouldn't mind (since you're a self-proclaimed LS1 guy), post some cam specs you would recommend for the heads I posted above. When I originally posted this, I had an LS1 discussion in mind, but I'm certainly not going to turn away someone with as much knowledge as Rich, from the conversation.

Something else I forgot... Why do the Thunder Racing cams kind of defy this theology? I would understand on a big cube motor having a reverse split, due to maxing out the flow of the LS6 intake. But on a 346, why does say the 230/224 cam perform like it does?