[TIN TIGR]

how do ya feel about smaller tubes and less lobe separation..does anyone have real numbers?...theorys are welcome also..pleez do not make this into a cv/vs std style head bashing thread, or some personal deal..

and how does this equate with stroke, if at all?..carb size?..compression?

[screamingchief]

Less lobe seperation,,,I dunno bout that...

By "less" lobe seperation do you mean a narrower,or wider LSA?

Generally "less" lobe seperation means narrower LSA's.

So I have a feeling many folks would suggest more (wider) lobe seperation was prefered.

Perhaps you meant to ask us about less overlap???

Now most will likely agree with that,,,that is when compared to an otherwise identical wedge head engine...

The "theory" tells us that canted valve heads generally tend to scavenge better than wedge head engines,and that would also mean they generally tend to prefer less overlap,and thus wider LSA's as a general rule,but there are plenty of other things to consider in that selection process as well.

And long stroke combos generally follow that same basic school of thought as well,less overlap needed,and thus wider LSA's tend to be prefered.

Also as the compression goes significantly upward,that too tends to like a wider LSA as well.

Though as the RPM range goes up,often that wants a bit more overlap to help the high RPM breathing,but it will still prefer the wider LSA often too,so you then need to look for that additional overlap from a source that wont be overly affected by a wider LSA.

But duration is often the wild card in all that.

Honestly,pondering the "prefered" LSA without knowing things like the cams "targeted" duration numbers,or the engines approximate compression ratio,or it's intended RPM range,it would be difficult to have any idea what would be "best",as that lack of info would make almost any useful dialoge on the subject a hit or miss proposition at best.

Duration and LSA go hand in hand with one another,and those are often chosen largely on the compression ratio of the engine,and the RPM range one is wanting to operate in.

Things like stroke and rod length are often felt by some to be secondary considerations in the process.

A cam is how a builder often answers these other "compromises" a given combo will inevitably have,so often the cam itself is a compromise of sorts,give here,take there,and try to strike a balance that will get one what they are after.

As for tube size,often that will be another source of much heated debate too.

Some builders will build the combo with a certain "size" in mind and then after some run time (dyno or ???) they will monitor the exhaust port coloring to determine how well the engine is doing in terms of scavenging efficiency and such,then make any adjustment based on that info.

The "theory" behind all this will always be debated,I personally dont really subscribe much to any specific theory or school of thought,and tend to prefer a more open minded approach to this sorta subject matter,I like to take a bit of everything into account.

Take any & all info with a grain of salt,even this post.

[Gach]

screamingchief....that is the best description I have ever seen given PERFECT!
Your right on the money!! My guess given all the details and goals you no doubt
could come up with a good cam choice...I see you get it.

[mysticmissle]

mines 113 results to follow

[BruceWilkie]

Brett well stated!

I'll add that the valve lift curve ties in with duration lobe sep and stroke. RPM band you want to be in plays heavily on your duration choices. A cv1 head on a 505 is going to have enough intake flow to support power at 7600 rpm, 8200 on a 468, 9300 on a 412! HOWEVER the exhaust will likely temper that down some unless its really well scienced.

If you are building say a 468 you dont want to go anywhere near 8200 in your stock block. You do want to take as much advantage of available flow as you can. This takes short seat timing and a fast lift curve. The std 1.7 rocker helps this acheivement and a 1.8 offers more. (moderately radical lobe more radical valve lift curve) ironically the seat timings and lobe profile ultimately determine the LSA and ICL. This affects not just overlap but the overlap window AND the BIAS of that overlap. (cam centerline relative to LSA) It is NOT unusual at very high rpm to benefit more from retard than advance.(something we dont see much of in the low rpm world we have been in with our Pontiacs.) It has much to do with air/fluid dynamics. If you approach with a set LSA in mind or ICL you could lose a lot of efficiency.

The exhaust on ANY combo will make or break it. The old street theory of as long as the ID is the sme size as the exhaust valve you'll be ok doesnt fly when you want to extract high ve from your motor. On the CV1 or most any high power combo its going to take an ID at least 1/4 inch larger than the exhaust valve.

For some insight to good basic exhaust design that applies to evrything read this Vizard article a few times. http://www.superchevy.com/technical/...exh/index.html Then tie it in with how it relates to cam timing. Not really mentioned in his overlap scenario but important to keep in mind is at lower speeds and/or low lifts, there are beneficial pressure exchanges going on even if flow demand is low at that point.

Pipemax (and others) is a good software tool for getting a scientific exhaust designed.

[TIN TIGR]

the reason i asked is becuz i am really drawn to try the other way..i have cams in the 106-110 ls area..and 1.7 or 1.8 rockers..not big duration..having tested the heads my 440 should clear 660-700 hp quite handily..while its not a world beater, it should be a fun beastie with zero maintenance..the pipes are 2 inch, which i believe is small for these heads also..just seeing if anyone else has gone this route..

[Gach]

Tin...if it where me..here's the way I'd go...264/276 @ .050 with 730 lift on a 112
with a 446 lobe and 1.6 rocker gets you to 730 lift..add 1.7 will get you to .780 lift.
and pick up the duration a tiny bit 267/279 and keep the motor in the 6500 - 6800 rpm range. The CV-1 flows 20 cfm more then my wide ports. If I went to the CV-1
I wouldn't change my cam just the rockers. I made 761 hp with 10.80 compression

[Motor Daddy]

If it were me I would ditch the 10' crank throw and get a 3.75" stroke crank in there to make some serious high RPM power to go along with a serious rear gear to make some serious rear wheel torque at a seriously high RPM, to seriously get down the 1/4 mile in a seriously short amount of TIME. But that's just me. Carry on.

[goquick]

With the 2" headers, I'd say depending on your compression that a tighter lsa may work, albeit a peakier power curve. Look at for example the super tight lsa engine that Kaase used in the EMC. Now that engine will look great on the dyno, but in real life, the 6100 rpm peak would be low and in a car, might be surprisingly short winded. But
it would be brutal up to that point. But you would have to run racegas to keep it together with that much compression.

[BruceWilkie]

Originally Posted by TIN TIGR

the reason i asked is becuz i am really drawn to try the other way..i have cams in the 106-110 ls area..and 1.7 or 1.8 rockers..not big duration..having tested the heads my 440 should clear 660-700 hp quite handily..while its not a world beater, it should be a fun beastie with zero maintenance..the pipes are 2 inch, which i believe is small for these heads also..just seeing if anyone else has gone this route..

The high ratio rockers IS the plus. Short seat time, fast lobe, hi intensity, big .050 duration relative to seat time, IS what these heads want. DO NOT PICK THE CAM BY LSA ICL OR .050 NUMBERS ONLY. A shorter stroke MAY end up at 108 to 110 LSA but that LSA and ICL are the COINCIDENTAL angle of the centerlines of the proper timing and shape of the valve lift curve in relation to flow curve stroke rpm and header/collector, intake characteristics.

In your application the following concerns need to be answered. FIRST, What maximum rpm do you wish to turn? If you are drag racing you typically on average end up with shift points 8 +/-2% above peak power. SECOND If you are a street car you also have to decide just how high a stall speed you are willing to run. (and that itself is very tricky as my old 440 flashed over 5200 yet cruised at 55 mph 200 rpm lower over the same long overpass than the previous 3200 flash convertor it had. that overpass was long and modest grade on the way to the track. I ran a 4.10 gear and 285/60 tire and had properly calibrated my speedometer. The street convertor would take that grade at 3400 rpm the race convertor was 3200 for the same 55 mph. Both at light load level approx 2800. Tight traffic normal "grandpa" type starts neither flared excessively.) THIRD, is trans type and gear ratio. FOURTH, what weight?

This is important stuff. You have to determine your power curve requirements. High flowing heads need far less duration at the seat than low flowing heads for the same RPM bands. You can get very good low-mid rpm tq numbers with the high flowing heads even if the peak tq rpm is higher than with the lower flowing heads. In other words the lower numbers are still better than before and the pk is at a higher rpm.

FWIW I was looking at a typical 400 stroker 462 and CV1 and found a hyd roller combo that could make 630 hp at 6500 pk tq of 580 near 5000 rpm and over 500 ft lbs at 3000 thru 6500. Using 1.8 rockers lift is at .657 the .050 numbers are only 238/250 The LSA on this one is 108 and advancing up to 4 degrees benefits low rpm without shaving much off the top of the curve. This was using an 850 carb and headers in the 2 inch od range and a 1.71 exhaust valve. Compression set at 11:1. The seat timing at 108/108 LSA/ICL bleeds the dynamic compression sufficiently for 93 octane. I didnt check with it adv 4 degrees.

I had to keep shrinking duration to bring the power peak rpm down because of the additional seat time of the hyd roller. A solid roller or solid flat could make for much better power curve opportunities.

[Motor Daddy]

Like that:

My power band would be 7500-9500, "Dat's it." Average HP is roughly 875 throughout the run.

[440GP69]

That Lifter accel rate is Slowwwww should be around 5-6, Stock intake valve is 2.25i and 1.66e with larger an option for CV and clears 4.155 bore FWIW

[Motor Daddy]

Originally Posted by 440GP69

That Lifter accel rate is Slowwwww should be around 5-6, Stock intake valve is 2.25i and 1.66e with larger an option for CV and clears 4.155 bore FWIW

All fixed. I was 100 HP down. Average HP is now ~975 throughout the run, from 7500-9500.

[TIN TIGR]

yes professor wilkie..your last example is about where i was thinking..but i am not afraid of rpm..or high octane..or even fuel injection..

and motor daddy..i like that one a lot..not for this go round however..but it sure has a place in my heart as a really cool idea..

thanks to all..i think its fun to discuss these problems, dont you.?.

[TIN TIGR]

i did not specify..these are agressive solid flat tappet designs..and compression ratio is not set yet..the heads are 65cc versions, so even with flat tops we can get it up there

[BruceWilkie]

Originally Posted by motor-daddy

If it were me I would ditch the 10' crank throw and get a 3.75" stroke crank in there to make some serious high RPM power to go along with a serious rear gear to make some serious rear wheel torque at a seriously high RPM, to seriously get down the 1/4 mile in a seriously short amount of TIME. But that's just me. Carry on.

MD See MY post relavant to that over on PZ(418 combo)

[Motor Daddy]

Originally Posted by BruceWilkie

MD See MY post relavant to that over on PZ(418 combo)

I don't PZ, I PY.

Alright, let me go find it.

Yup, the good old 13.9% theory is in full effect.

[BruceWilkie]

Originally Posted by TIN TIGR

i did not specify..these are agressive solid flat tappet designs..and compression ratio is not set yet..the heads are 65cc versions, so even with flat tops we can get it up there

A really agressive solid like comps xtq series can get near solid roller results. CliffR had disappointing results with those lobes with his KRE combo however all indications are the cam was chosen based on .050 specs the seat timing was only 269/277 and .050 is 240/248. Would be a nice cam for a 350 so I bought it from him.

Please no need for the professor stuff. Give me an RPM peak, a compression ratio, and a flow chart if the heads arent out of box CV's and bore stroke. I have a wide choice of Bullet Erson and Comp flat tappet lobes that could be used if you dont want a roller. That hyd roller was an example of a fairly wimpy cam and the power results reveal the cam is no where near using the potential of the head. You could give me adv, .050, .200, durations lobe lift rocker ratio LSA of the cams you have to see how they work.

Again you do not chose a cam based on .050 spec or LSA regardless of what the magazines say! They are best used as reference points when degreeing a cam! Also I can spec a cam that makes max power at peak rpm or better I can spec a cam that makes most average power in the race rpm bandwidth(stall to shift point). Wide LSA doesnt ALWAY mean wide power band and narrow LSA does not always mean narrow peaky power band as often as that is suggested. Longer stroke vs shorter stroke engines pistons DO NOT spend more TIME in dwell at tdc/ bdc but the piston DOES spend more crankshaft DEGREES there vs a shorter stroke. (relative to our Pontiacs strokes at 3.75 or greater and rod lengths within physical constraints)

The .050 adv and .200 durations along with lobe lift give a loose idea of the lobe character/design. LSA and overlap are the mathematical results of the cam timings and centerline results of those cam timings.

[TIN TIGR]

yep..before i pick the first cam, i am gonna map all 4 out..get all the real numbers off the cam itself..i have had brand new big name cams come thru offset ground from specs..when i get all those numbers i will let ya know..a good set of flatops will give near 12-1 cr..

tire size is mandated at 10.5 x 28, or a 275-60 dr, both 15 inch

we wont address the nitrous kit yet..

[BruceWilkie]

FYI Erson qc spec is a tight 0.00001" and 0.1 degree. Ask bankbook over on py how far off his comp cam was.