Orr89rocz

iTrader: (13)

Its just the flow characteristics in the port itself. Some guys who do take a good look at e/i ratios find that more duration split on higher e/i ratios hurts power. Some guys only worry about the discharge velocity profile and such across the exhaust port and dont worry about flow.

You can always get the exhaust side to work with the right cam. Top Fuel engines can make near 8000 hp but the exhaust valves arent that big. Same with n/a pro stock type stuff, intake valves are huge and flow alot but the exhaust side is not big at all.

I'm not sure where i stand with e/i ratios because it depends on the port type. Rectangular port L92 type head may not show good e/i ratios but the exhaust side does flow a good amount of air. Its just offset by the huge intake port side that flows so much. Typically takes a different cam type tho but i've seen lower duration spreads work too on these

Rickenbackerman

iTrader: (1)

I know Tony's talked about this elsewhere on here (and Tony correct me if I've got this wrong), but my understanding is that since the exhaust ports flow so well, by opening the exhaust valve early due to too much overlap, you're letting some of the unburnt charge out the port that would be better served staying in the chamber to continue burning and doing what it's supposed to do - push the piston down and make horsepower. "Normal" heads may like some overlap to let the escaping exhaust gases help pull the next charge in, but AFR's don't need the extra help.

Tony Mamo @ AFR

iTrader: (13)

That covers it pretty well.....(nice job btw!)

I have more to add about this entire situation but Im a little pressed for time now.

The abridged version is the OP's gameplan doesn't allow for the right compression with a low 230's cam....especially on a tight LSA (which is a mistake with the AFR 215 head anyway).

Basically your forced to run unmilled heads otherwise you wont have enough piston to valve clearance.....certainly not enough of a window to be comfortable. Now your static compression sucks and your DCR is even worse....coupled with a sizable cam the low end response will really suffer and it will take alot more RPM's to start pulling hard.

So I ask you....do you want "alot of lope" and a car that under performs, or a more moderate lope (clearly not stock and still sounding healthy) that runs like a scalded dog because its "cylinder pressure management" is soooo much more effective.

Its counter intuitive.....the car sounds intimidating and doesn't run hard....not to mention your drivability and low RPM responsiveness sucks from the additional overlap, and you have cam surge at part throttle to deal with as well (and a peaky power curve with very little area under the curve).

My optimized 224/228 cammed car (my C5 when I had the stock shortblock and AFR 205's) sounded mild but would put cars that sounded twice as mean on the trailer.....and I drove home from the track smoothly knocking down 27+ MPG on the freeway. Not suggesting we have to go quite that conservative but the point Im making is a winning combination (IMO) is more important than its ability to intimidate (some) at a traffic light.

Will get into this in more detail if necessary when I have more time....but I kinda highlighted the larger issues I wanted to discuss and give some of you guys something to chew on and think about.

-Tony

RonSSNova

iTrader: (3)

Ah, I also caught the term "a lot of lope". Trust me, there is nothing like beating up on the rump rump guys with a sneaky fast mild sounding car.
When you tell them your combo they won't believe you and will accuse you of having a hidden bottle or a much larger engine.
Especially when you drive it out the gate.
Ron

Rickenbackerman

iTrader: (1)

I LOL'd at "rump rump guys".

mac62989

iTrader: (1)

Tony, are you saying a smaller cam would work better with these heads? What did your car put down with that setup? Most of the other **** you said went way over my head...

Tony Mamo @ AFR

iTrader: (13)

OK....

The subject of cam "lope" (aka rumpety rump!) has been brought up in this thread and I get it alot (in PM's) and I see it alot on this board.....lets face it alot of guys want it and while Im not completely adverse to it I think people need a better understanding of whats really going on.

Let me lay out a couple of scenario's just for fun that should help educate those unclear about this and it might prevent some from going down a road they might not be happy with in the end. Note much like the OP's situation in this thread that this exercise assumes we are dealing with a stock shortblock and NOT flycutting pistons which as most of you know is very prevalent around here.

FACT #1.....When we are modding a stock shortblock, we have only "X" amount of comfortable piston to valve clearance to deal with due to no notches/valve reliefs in our stock pistons.

Scenario #1.....I see alot of guys go for larger cams in the low or mid 230's @ .050 and leave the heads stock (or very close to stock) regarding chamber volume and gasket thickness because they need the extra room to have enough piston to valve clearance for the "big" cam their confident will yield them the most power (and sound cooler with more lope).

FACT# 2....A tighter lobe seperation angle (LSA) will always reduce available piston to valve clearance.....always. A 232/236 cam on a 111 LSA will have alot less P to V than the same cam on a 113 or 114 LSA

Scenario #2.....Lets run a slightly smaller cam (not a wussy cam mind you) thats lets say 227/230 @ .050 and run it on a wider LSA reducing overlap and increasing available piston to valve. This allows us to do two things.....drop the gasket thickness to optimize the quench distance and also mill the heads....both of which are ideal for increasing the static compressions (and the DCR) of the combination.

FACT #3.....Compression is GOOD (think of me right now as the "gear head" Gordan Getko telling you that.....LOL). Hope you guys get the joke.....but seriously, compression is good because compression is cylinder pressure and cylinder pressure is what this game is all about. You want as much compression as the octane your running will tolerate. It will make more torque, hence more power, and it will even increase your fuel economy and engine responsiveness. In fact its one of the few things engine related that doesn't have any negative trade off associated with it (big cams make more peak power but hurt the bottom....some manifolds will boost peak but hurt the bottom.....you see where I'm going here).

Comparing Scenario #1 and Scenario #2

While #1 will look good upstairs (peak power), it will be a dog down low....you have to much cam for too little compression.....this destroys DCR btw and the engine is much more sluggish and lazy than it needs to be. It will lope hard (lope is simply overlap) but it wont make much cylinder pressure, it will give you cam surge, and you just threw your fuel economy in the toilet as well.

#2 on the other hand will sound more mild....it has a smaller cam, a wider LSA, and more compression which tends to clean up the low speed response some. It wont sound as intimidating cruising through your favorite burger joint but it will have a cackle and a crispiness to its engine note that will get the sharper guys interest I assure you (think of the idle quality in my 383 Vette video as its cackling at an idle right before I drop the clutch and spin the tires thru the first three gears).

FACT #4....A wider LSA cam has a later intake closing point (than the same cam with a more narrow LSA) and intake closing point is one of the most important aspects of selecting the right cam. Cams with later intake closing points tend to peak later and carry the power better past peak. Why is this important.....because it helps the shorter duration cam which boosts low/midrange power also make good power upstairs....and this is bonus.

Back to discussing the #2 (milder) combo's power curve. Due to all the factor helping the low speed power (more compression, smaller cam, better quench), the #2 combo walks all over #1 if you were to layover and compare the two hypothetical power curves we are discussing. I'm talking about serious advantages down low.....to the tune of 40 ft/lbs or so. In fact scenario #2 is a cylinder pressure capturing machine and it will handily beat #1 through potentially the redline of the combination but the curves will get closer and closer with RPM and probably end up somewhere around a tie or so at very high RPM.....maybe....truthfully I feel #2 might eek out #1 in peak power as well but I'm more concerned with making a point here and explaining how the power curves would trend.

A picture would tell a thousand words....I will try to post something later if I get the chance.

Scenario #2 also is extremely responsive, gets much better fuel economy, has minimal to zero cam surge, and much stronger "tip in" throttle as well.....its just a crap load more fun to drive.....feels immensely more powerful and has alot more "area under the curve" power and obviously more average power than Scenario #1. As you guys should expect at this point it will also walk away from #1 at the dragstrip (and from a roll on the freeway) because its going to leave harder and recover from a shift faster as well. If we are discussing road racing forget it.....#2 will be lapping #1 in short order.....no contest.

So all of this is what I didn't want to get into yesterday knowing I had alot to say.....

Sorry for the novel but this is interesting real world sheeet and I hope it helps some of you guys that are on the fence as to how to approach building your car.



Cheers,
Tony

RonSSNova

iTrader: (3)

Well said mr. Wall Street.

Ron

Tony Mamo @ AFR

iTrader: (13)

OK....here is my hypothetical dyno overlay of my hypothetical combinations I discussed above....LOL

Sorry for the quick freehand drawing (worked in the pinch!) but I assure you the overall look and shape of the curves is exactly what the two scenario's I discussed above would yield out in the real world.

I decided to show the low compression larger cammed engine shine a little past peak where is finally trumps the #2 curve but its too little and far too late to have any effectiveness. The usable average power and torque handily go to the smaller cammed high compression combination even up top where you would be racing it and looking at the lower/middle part of the curve there is simply no comparison.

To be honest they might have only met evenly at the end of the curve or even been slightly reversed showing a clear victory for Combo #2 the entire curve, but once again the point here is to help you guys visualize what I'm talking about and make it easier to understand.

airforcemanss

iTrader: (23)

i have afr 205s with brand new springs on the car right now. lmk if interested im trying to lower compression an go boost.

Tony Mamo @ AFR

iTrader: (13)

I think Airforceman is wanting to sell some 205's (well I know he is via a quick PM chat and my recommendation to do so).

Kinda in this thread but none the less let me keep the tech train running and finish off what I set out in this thread to clarify.

What we didn't discuss is the guy who wants (and likes) lope and is willing to flycut or replace his factory pistons (and also realizes an engine of this nature is only going to be primarily about high RPM power).

IMO this scenario (which we will call scenario #3) is one worthy of consideration if the potential owner realizes what he is getting into and the additional risk and maintenance a higher RPM engine is synonymous with because that is essentially what a properly designed combo with a larger cam will do best.

The biggest difference between this combo and combo #1 is this situation (a piston with valve reliefs) allows us to mill the heads a bunch and run a thinner gasket for more compression and a tighter more efficient quench. Instead of 10.8 ish like the first combo, this combo will be about a point higher than that and due to that fact will have a much better DCR figure and it will make more cylinder pressure. It wont be as lazy down low, and it will come up on the cam a little faster than the lower compression approach we discussed earlier. The additional compression erases some of (but not all of) the negative traits associated with combo #1, and it will make big power upstairs carrying well past both the former combo's we touched on above.

Here is the same engine as the first two combo's but with a larger cam (lets call it a 235/238 grind) and more compression.....in fact a little more than combo #2 because a bigger cam bleeds off more cylinder pressure so it can tolerate a higher static CR (and like it I might add). Thats another reason why #3 can make more peak torque than the #2 combo but it will happen later in the curve and it will never look as good on the bottom (compared to #2) primarily due to the much larger cam.....that's always a trade off your going to have to make if you want to go "big". Obviously the dashed line is the #3 combo I just highlighted



Now IMO, this becomes a more worthy situation if your looking for alot of lope. It will actually out perform a combo built similar to #2 (by a small margin) but of course will never be as easy to drive around town nor will it be as fun and "spirited" in the lower revs, BUT....at least your getting something performance related with your "lope".....now not only does your car sound mean, it can run the number as well and if you like an engine that pulls upstairs and seems to never lay down this type of combination does that (but all this assumes painstaking details have been addressed regarding valve control.....that includes minding your valve weight, type of rocker arms and lifters, the right valve springs, even pushrod choice.....without perfect valve control which is more difficult to achieve at higher RPM's, combo #3 wont look any better than combo #1).

And all it takes is being willing to flycut which really isn't a big deal, or willing to change out your pistons (which is a big deal and if your that far in you might as well go 383!).

Anyway.....half the reason I spent so much time writing this was to refer potential customers I'm speaking with here because its a common situation. I also felt it was directly applicable to all the OP's concerns and hope that he also somehow benefited from the time I invested.

Catch you guys later



-Tony

Orr89rocz

iTrader: (13)

Yep as long as you gear/stall it correctly to use the power where its made, who cares whats downstairs in the power band below stall level. With most converter cars I cant tell how low end feels under the stall point rpm anyway. I agree that big cams for big peak power require compression. These motors like having higher cylinder pressures/higher cranking pressures.

Tony Mamo @ AFR

iTrader: (13)

Good point....and this is what I meant when I said the customer needs to know what he's getting into.

Its not uncommon to see a thread about a guy going with a smaller cam after living with all the negative side effects a larger cammed combo brings to the table. The more aggressive you get, the more single focused the car becomes.

Its better to shoot 30 RWHP lower and try to build an explosive better all around combo with a fat power and torque curve if you plan on really driving the car alot.

If your building a Friday night street race toy thats a completely different story of course.....only you know what you plan to do with the vehicle and taking the time to weight the pro's and cons of what your really embarking on (and examining your budget to do so) is just smart.

Too many people get caught up in the numbers game and they aren't really prepared for what it costs to get there or what they will have when the smoke clears.

-Tony

Rise of the Phoenix

iTrader: (27)

Tony, thank you for all the great information you've contributed to this thread. Your knowledge on this subject is far supperior to anyone else out there. You had mentioned a cam around the size of a 227/230 being a far better option than a 232/236 cam for a stock bottom end 346 without notched pistons. Would a 112 LSA be ok for the 227/230 cam, or would you recommend the LSA being 113 or 114. Thanks again for all your help Tony.

Tony Mamo @ AFR

iTrader: (13)

No sweat.....appreciate the opportunity to use your thread as a podium of sorts to try and help with a topic that I feel is often overlooked and completely mis-understood.

Regarding your cam questions, small cams need wider LSA's to help them punch a big number (in some respects giving you the best of both worlds concerning the power curve) and the 215's in particular are extremely strong in low lift exhaust flow so that is another factor that favors a wider angle LSA (promoting less overlap) and also a consideration to use a single pattern cam. I would stay 114 in your application....and probably run with a 227 or a 228 degree single pattern grind here.

I would like to help you design a package if your up for it.....shoot me a PM and we can nail down some of the details and perhaps we can revisit this thread later with actual dyno results. I think that would be kind of interesting for the guys who might want to follow the thread.



-Tony

PS.....Good luck regardless and I hope you have a better understanding of some of the dynamics involved.

Rickenbackerman

iTrader: (1)

I know for sure I'll be posting a thread in the dyno section with numbers and 1/4 results when all is said and done with my package, which sounds pretty similar to the OP's situation (although my car is a street car and not at all set up for drag, I'll still take it to the track this spring).

I think that's the first time I've mentioned the evil word *DYNO*. Tony and I haven't once discussed numbers, cuz I don't give a rats *** about dyno numbers. MPH in the quarter is what separates the men from the bench racers.

edit: not to mention doing so while still retaining excellent driveability, part-throttle response and the ability to pull the stock-headed "rump rump" guys (I was one).

99Bluz28

iTrader: (35)

Great thread, It's got me rethinking my current 227/231 111lsa +2 cam with unmilled AFR 205s and stock compression. I wonder if a switch to a 227/227 112-114lsa +3 would would be worth it for a power increase below 4500rpm, if there's any to be had ?
http://i523.photobucket.com/albums/w...aph2011001.jpg

Rise of the Phoenix

iTrader: (27)

Who specked that current cam for you? I'm no expert, but why not mill the heads some. You'll pick up some more torque and horsepower with whatever cam you go with.

99Bluz28

iTrader: (35)

Yeah, that's going to happen some time in the next year or two, but I'd mainly want more power below 4500rpm. A lower overall power band that I can actually make more use of on the street.

DarkblueTA

Tony, great info. Thanks for sharing.