DenzSS

I'd really disagree with that. I know a lot of builders that have went to great lengths to work in the longest rod they could. Just depends on the engine. I would have liked to have stuck a longer rod in my 408, but we did what we could.

Rod length is critical when determining the characteristics of the rotating assembly. The rest is cake.

JS

iTrader: (4)

Denz,Could u give a cam spec giving your 280DFM head combo shifting at 6800?

Also I like what Cstraub said about tq but everytime u make a post on here about tq people say hp is the major factor.Now I agree that for a light car leaving the line at 6000+ tq isnt as important as hp but for a guy like me who likes to eat and has a 3550lb car running a A4 I would think TQ TQ TQ is what I shuold be looking at for maximun ET?

Am I wrong in thinking this way Denz/Cstraub?
Lastly here in my dyno graph,This is a LS6 Head/224-580 cam 113 +2
My car HATES exhaust,It picks up 13RWHP and 20RWT by opening up the cutout?

I like my HP/TQ curve on this sheet,What converter/gear would u run with my setup for MAX ET.I'm peaking at 4700 TQ and 6000 HP carrying it to 6400.I was thinking a verter around 4400 stall/4.10 gears and a 26in slick?

I was going to shift it at 6500
Am I close?

Cstraub

iTrader: (1)

JS,
No your not wrong, for most part we are dealing with daily drivers. . .and what most want is stop light to stop light power. Because of the limiting RPM factors of a hyd. roller, torque is where its at. Now if these were 2Klbs cars with 288 CID v-8 and a glide, then we can talk HP.

Cam is dependent on what Denzss and I have discussed, combo, head/intake flow, and desired power range. Looks like you have some type of modified head, so I would suspect that with the improved flow, the exhaust lift you have is a culprit.

Chris

DenzSS

I can see why you like your dyno sheet. Your car is basically F-up proof. Flat curve, easy to be consistent. If you shift a little early or late no big deal (well, if it was a M6...with an A4 you're shifting consustently anyway).

As far as cam specs go, there isn't much I can really do. I could post a few that I know work well, but I have two problems. If I posted the standard duration/lift/lobe seperation it wouldn't do anyone any good. If I posted the mid-lift numbers to show you what the lobe is doing, the guys I work with would slaughter me.

Having said that, durations are similar to what is being ran as the middle-ground camshafts. The lobes, however, are widely different. Nobody wants their lobe information out there because it is giving away their hard earned work. That is why I recommend the TR224 to people. It is a
good off-the-shelf camshaft and Thunder Racing did the work on it. I'll buy one from them before using a knock-off.

As far as torque goes, Cstraub and I are pretty much in agreement. Heavy car + heavy driver = torque. You have to get the thing moving and accelerating. There is no reason to launch the car off the rev limiiter at 6500rpm if you can make torque to get you off the line and accelerating at a lower rpm.

IMO, 4.10s and a 4400 are overkill. 4.10s in an A4 can work, but it makes 1st gear a really short spurt. If you make the torque in the engine, you don't need as much of the multiplication provided by your gears.

With your hp/torque curve, you could run a 3000-4500 stall converter and make little difference one way or the other.

JS

iTrader: (4)

Thanks CStraub....So the 6500 shift/4400 Stall/4.10's and the 26in slick should be the ticket?

But when u say culprit (YES they are ported LS6 Heads) what would help correcting this problem and would it effect my car once I opened the cutout.Guess what I'm trying to say is could I pick up some power by changing the cam without sacrificing my mid range TQ and keeping my shift point at 6500.

I run my car threw a cutout and wont ever change.
It works,and this way I'm fairly quiet on the street when its closed

DenzSS

Yup, you could pick up more power through the same range. There are significant gains to be made over the 224/.580" camshaft you are using, but you need to figure out how brutal you want to be on the valvetrain. Do you have the flow sheet for your LS6 heads?

JS

iTrader: (4)

Well Denz, u made my day..
What if I kept the 4.10's but ran a 28in slick to combat the quick gear change.
Would this benefit me or slow me down being the tire causes more rollout?

IMO TR224 is the BEST all around cam out there to date.Even on 112LSA is idles VERY WELL threw 6sp/auto and makes KILLER midrange power.

LOnSLO

iTrader: (15)

I'll have to agree on what you guys are saying on the TR224. That is probably the best street cam out there. The off-idle torque is incredible. Not the best drag racing cam, but not bad either.

DenzSS

28"/4.10 will work, I can't say how well. I have a pretty good understanding on the engine side, but I'm not a big drag racer. You'll gain about 4mph on your 1-2 shiftpoint. I'm just not a big fan of 4.10s in an A4 car that has some street time. Hopefully someone will hop in that is a better resource that me on that subject.

224 is a very good cam for most people. It can be improved upon, that is where custom designs come in. The TR224 is designed to work pretty well in just about anything from stock heads to a good port job. Kind of like Windows (even though I hate that damn OS). A custom cam is more like Linux. It takes more work to set up, but works better once your done. Make sense?

JS

iTrader: (4)

So if u had the choice the 4.10/28 is better than 26/4.10 for my car.

JS

racer7088

Like Who? In race classes where you can lose block height and rod length they always do it. Look at PS car and truck. They give up lots of rod ratio possibility by taking almost an inch off the blocks and they are ONLY concerned with hauling ***.

I like longer rods for almost any combo but again I wouldn't destroke or run too short of a piston for a longer rod ever and I've never seen anyone else that knew what they were doing do that either. I know several Comp guys run shorter than stock rods all the time for high rpm stuff on purpose since otherwise they have extremely long rods which can kill power and acceleration. A ten thousand RPM small block PS motor has shorter rods than a stock SBC or LSx by a lot.

DenzSS

I'd agree with a good portion of that, but it depends on the engine in question. I wouldn't destroke an engine (in general) to stick a longer rod in either. It is, however still a major consideration. Just like camshafts, you're trying to get the right amount of rod length for the job. Sometimes you can fit in the rod you want, sometimes you can't. Hell, just look at a standard 355 SBC. A 6.00" rod makes a better acceleration curve than the stock 5.700", but a lot of people don't want to go to the work of clearancing for the longer rods.

It also depends on whether you're running an endurance engine or a drag engine. Different beasts as we both know.

If you want, post the rod length and stroke of some of those motors and I'll post a few plots of the velocity and acceleration curves.

Damn, somehow we got into the age old long vs short rod argument. Where are Yunick and Jenkins when you need them.

racer7088

DenzSS,

BTW I do usually run as long a rod that will work right so I'm not saying that I think longer rods are always evil or anything. You do get a lighter piston at least that way and a little less side loading from longer rods but again I wouldn't run a taller deck or extra short piston thinking that I would gain something from the rod length. If you noticed WJ and Kaase ran LONGER STROKE and SHORTER rods on the BBF to win the engine masters challenge with the SCJ Kaase heads not the other way around. They are both great engine builders.

Ed Curtis

Might be because they wanted to shorten the inlet tract??

Well... in my dumb-*** opinion, in the old days when the cylinder heads were a big problem, the correct usage of rod ratio "would be" considered and was a factor in an engine build-up. Today, with what is available for cylinder heads, it's kinda moot. Though I still like a longer rod (high R/L) in a "bad head" or restricted camshaft application, there's no rules or limitation placed on these LS1 combinations so who cares. It's not like there's a rules dominant "Heads-up" sanctioning body just for LS1 cars to hold anyone back.

Ah yes... the key word.. "ACCELERATION"...

Dynos be damned...

Ed

DenzSS

Don't most BBF's run around a 6.6" rod with a sub 4.00" stroke? On that configuration, they can afford to give up a lot of rod length. They can go all the way down to a 6" rod without gaining much in the way of jerk, especially considering the rpm range used in the challenge. I didn't follow the challenge very closely. How much jerk is too much is something I can't say. The pros can, obviously, but it is out of my range.

99 Black Bird T/A

iTrader: (4)

Black Bird’s ghetto math…

Racer thanks!

(CID/2) * 6500 rpm/1728 per cubic foot = need air flow

cam duration divided by 720 degree = percent of time to get the air per revolution

needed air flow divided by percent of time to get the air in per rev is cfm needed

346

(346/2)*6800/1728 = ~681 cfm

651/8 cylinders = ~85 cfm per cylinder

208 cam (LPE GT2-3 cam)/720 = .289

81.4/.289 = ~294 cfm

So the little LPE GT2-3 (208/220)cam can do the job just as well as a BIG cam IF the heads work with the intake to flow ~295 cfm thru the intake.

383

Basically the heads Denz mentioned could also work for a 383 with a 240 to 242 sized cam based on the ghetto math. This is assuming the heads can flow ~283 thru the intake.

(383/2)*6800/1728 = ~754 cfm

754/8 cylinders = ~94.3 cfm per cylinder

240 cam 720 = .3333

94.3/.333 = ~283 cfm


Likewise, for my engine project 6500 rpm is about all I want to turn rpm wise.

346 for my 91 RS

(346/2)*6500/1728 = ~651 cfm

651/8 cylinders = ~81.4 cfm per cylinder

208 cam (LPE GT2-3 cam)/720 = .289

81.4/.289 = ~282 cfm

With heads that flow ~282 cfm with the LS6 intake in place my 346 should be ok with a LPE GT2-3 (208/220) or a Thunder OLD Man cam 215/220 cam if the heads flow ~270ish with the the LS6 intake.


383 for my 91 RS

(383/2)*6500/1728 = ~721 cfm

721/8 cylinders = ~90 cfm per cylinder

229 cam (MMS229v2.1 cam)/720 = .318

90/.318 = ~283 cfm

I know it's not quite this simple but this thread is a good tool to make us think about part selection. On paper it looks like my TEA LS6 heads, LS6 intake and MMS229 cam make for a nice matched stroker set up.

How do we calculate how much exhaust flow we need? Same way?

DenzSS

Yup. The calculation isn't correct, but it'll work just fine for what we're talking about. You have nailed the point of this thread dead-on. Higher flow does not equal larger duration camshaft.

Cstraub

iTrader: (1)

Maybe my "churches congregation" will get a little larger as I have always preached, better heads, less cam. Now with correct duration at .100, .200,.300 and some correct VE, I think Dr. Denzss the're is some power to be had.

Chris

JS

iTrader: (4)

I can tell u guys way back when I had a MILD set of 241 castings ported every so slightly with STOCK valves,LS6 intake and the TR224 cam,4200 stall and 3.73's the car was SNAPPY AS HELL.

If u hit the throttle it was at 6K in a nano second
The best part is it ran 11.30's@118 at 3450lbs shifting at 6300 rpm.
Small runners w/not outrageous flow numbers (270FM) seemed to be the ticket,almost what Denz is implying?

I now have a big set of heads,bigger cam (just a smidge) and the car IMO didnt feel as snappy nor as torquey,so I adv the cam 2 degrees (shouldve went 4) and this has helped as u can see from my dyno sheet,I lost some peak HP but I could give a rats ***,I now have more tq across the rpm band.

So Denz,Whats its gonna be---->26/4.10 or 28/4.10 for my setup?
And would u drop the stall back to around 4200?Lastly a few drag racers told me to also look for my converter to drop no more than 900 to 1200 from my max shift point to my next gear change?

99 Black Bird T/A

iTrader: (4)

Just for fun I calculated what sized cam my old JPR Stage LS6 heads would need based on flowing a peak of 239 cfm with the LS6 intake in place.

(346/2)*6500/1728 = ~651 cfm

651/8 cylinders = ~81.4 cfm per cylinder

244 cam /720 = .3388

81.4/.3388 = ~240 cfm

Looks like about 244 sized cam is what it would take to move required ~280 cfm of air with those heads.