[n2ogpsj462]

what are the benefits of both? are there perticular combos that will work better with a single pattern?? just asking because i have an opportunity to purchase a single pattern comp solid. 248 duration/525lift. how would this be different from the crower 247/252 duration 507/517lift i planned on using. 462 252cfm 6Xs 9.3:1, rpm, 850 in a heavy car with a power adder.

[n2ogpsj462]

what are the benefits of both? are there perticular combos that will work better with a single pattern?? just asking because i have an opportunity to purchase a single pattern comp solid. 248 duration/525lift. how would this be different from the crower 247/252 duration 507/517lift i planned on using. 462 252cfm 6Xs 9.3:1, rpm, 850 in a heavy car with a power adder.

[Jack Gifford]

Somebody can probably give you a more comprehensive answer. But in general, a single-pattern cam leaves most Pontiacs a little deficient for exhaust flow.

[23t428]

Take a look at Isky racing cams website, there
is some good info on cam selection. Most pontiac cams are split duration & lift as is noted the exhaust definitcy. But when I spoke to one of the cam techs he made mention of application and in a racing only situation, where head porting, good set of free flowing headers, single plane intake, bigger carb and so on. The single pattern cam is a very viable
option ! I'am trying a Lunati hyd. cam with 235-
235 duration at .050 and .507" lift, I will be using 1.65 roller tip rockers for a lift of .557" in a .030" 428" in a front eng. dragster with powerglide and trans brake. Give Isky a call and checkout their website, after all they did supply cams to some of the fastest Pontiac's before many of us were even born. The
slogin Cam Godfather has deep roots. Good Luck
Poncho428 !

[Skip Fix]

Pontiac Jack, I think if you flowed some ported Pontiac iron heads(and even most aluminum) you would find the intake is the low side. Shoot even a good aftermarket SBC head designed to feed 350-400ci flow as good as what we have to feed 455ci!Depending on the intake to exhaust ratio on actual head flow different cams will work better. Just pocket porting some 6Xs and adding 1.77 exhausts and blending them got the intake to exhaust in the 85% range. My RAIVs are the same way.

75% or less split pattern 80% look at a single pattern, 85% or more maybe more duration on the intake side.

[WDCreech]

I remember reading, years ago, to run a dual pattern cam with D-port heads and a single pattern with round ports. But as Skip Fix stated, it all has to do with the flow ratio! I was running '68 RA IIs when I read this and have used a single pattern cam since with RA IVs and Wenzler High Ports. For D-port engine, I would look closely at the intake/exhaust flow numbers.

[Jack Gifford]

Skip & WD- thanks for providing the kind of detailed answer this guy was looking for, as to why dual-pattern cams exist. And I neglected to qualify my answer as pertaining to early stock heads.

[Skip Fix]

My RAIV motor liked a 242/236 @ 0.050 cam.Cut out all the reversion tyat was happening with a "normal" 4 degree split cam.

[74t/a]

Those are all great answers guys, but nobody ahs address the issue whether the engine is going to be running an exhaust system.

If that is the case, then you almost certainly will need to run a dual pattern cam.....with about 10* more.

A single pattern cam works great on a head with 80-85 % flow ratio as skip said, IF the engine is running with open headers, and the headers are "tuned" and correctly sized.

The exception to this is if the engine will be running NOS.

[Skip Fix]

Bryan I'll disagree with what worked on this motor, 400 RAIV. That was with an exhaust system(2 chamber racing Flows). Open headers no reversion even with the normal dual split cams, picked up .3 second. Through the exhaust a different story,reversion city. The RAIV exhaust port would flow 98% of its flow backwards(using the intake side of the flowbench). So even minimal backpressure without a good scavenging header killed it.The lobe sep/overlap also can make a big impact on this giving more time both valves are open for the reversion to take place.Headers also make a big impact. Going to smaller better scavening header made the world of difference on this combination. This was a 12 teen@ 110 in a 3850lb car with a Q jet. Since our Pontiac intake ports are slightly defeccient the added intake duration might be compensating there like a bigger rocker ratio just on intakes.

[n2ogpsj462]

my 6x4s flow 252/217 which is 86%. and im running nitrous. so in my case a dual pattern would be better with more on the intake??? you dont see many advertised cams with more on the intake usually vise versa. the crower i wanted was 247int 252exh. with a 112LSA. with 1.65 rockers. some say the rockers will change the duration slightly is this true?
thanks- scott

[n2ogpsj462]

also a 3" x-pipe with tail pipes is being used. prob either flowmasters or the pro-v's

[Skip Fix]

Some blower and old hemi cams had more intake duration,mine was a custom.Remember it doesn't cost much more(especially in the total price of the motor) to get a custom cam whatever lobe you like often different lifts same duration available, and whatever lobe sep and advance you want from any of the cam companies.

I'm not a nitrous expert but what I understand nitrous since it is injected/sprayed with the additional fuel is equivalent to way more intake flow so you need the additional exhaust duration to let it out. Also need a wider lobe sep 112-114 to decrease the chance of that extra exhaust blowing back up the intake during overlap.Maybe one of the N2O guys will make cam comments.

Add "equivalent" duration @ 0.050 of 2 degrees per .1 additional ratio over 1.5.

[74t/a]

Skip, therea re most certianly exceptions to every rule. I am surprised at the results you had with that particular engine.

It is very common to run a larger intake lobe on restrictor plate engines and limited carb engines such as 350 2bbl. engines used in circle track applications.

That must show you that your engine must have been a little short on the intake flow.

Scott, It really depends on how much nitrous you are planning to run. Give me somemore details on your combo, and I can steer you in the right direction.

Bryan

[buwalda]

I believe alot of these theories about dual pattern cams & LSA are a case of 'old habits die hard' and 'the factory used it, so it must work.' The 'factory' in many cars also used restrictive 2" exhaust systems, restricitve mufflers, no exhaust crossover & no headers! No wonder the exhaust needed help! But all that goes out the window once you upgrade the exhaust.

In the the recent Engine Masters Challenge in PHR magazine, there a few engine buliders using cams with MORE intake duration [ or put another way, LESS exhaust duration ]. The notion is catching on. What was surprising was that one entrant ran these cams in both it's big block & small block entry. They didn't come first in either Challenge, but they still stuck with more intake duration after not winning the first time. So they must believe it is better. Who was it? Crower cams. If anybody should know, they should.

In the end, you have to try it for yourself & your combination. I have tried several cams in my 455 & I find the engine runs better with less exh duration than the intake. Try it. You might get a pleasant surprise!

[Skip Fix]

The reason I tried that cam was the motor had had 3 different cams installed at various advance retards that were the "normal" dual pattern, one with only 4 degrees split. They all ran to the .01 second and had reversion issues.The Comp tech Bob Cook and I figured a single pattern wouldn't be that differrent so we wanted to make a big change. It paid off on that motor.

[Cliff R]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">I have tried several cams in my 455 & I find the engine runs better with less exh duration than the intake. </div></BLOCKQUOTE>

Geoff, if you don't mind, please describe "better"? What criteria are you using to described improved performance with cams having less exhaust duration, dyno, track, fuel economy, "seat of the pants", etc? If possible, I'd like to see a detailed analysis and what exactly was changed and how the test results were monitored/compared/recorded.

Here, we've ran single and dual pattern camshafts for a variety of engine combinations, but to date have never switched out only the cam and did another comparison. So providing specific and accurate information would be near impossible. It is my opinion however, that the large turn in the exhaust port of the Pontiac head combined with relatively small primary header tubes and backed by any sort of exhaust system has the Pontiac engine favor dual pattern camshafts. In contrast, well ported Edelbrock or other aftermarket heads and large tube well tuned headers most often favor single pattern camshafts.......Cliff

[Skip Fix]

Cliff my RAIV motor fits with what Geoff said, 3 different cams,different positions, nothing else changed. mid to low 12 car with ful exhaust.As Bob at Comp and I decided try something way different! You never know until you do. Possibly using more rocker on the intakes of a single pattern would be close to s similar test. Maybe something for a dyno test at KRE!

[n2ogpsj462]

74t/a motor is 462 6x4 heads i had done and the porter said he did the short turn for good low lift flow. flow was 247/197. after the 1.77s in the exhaust were added and RAIV ferrea valves were installed flow was 252/217 at 550 lift. headers are rons tri-Ys, rpm intake i opened myself to 2.20 and i planned on milling the secondary like jim hand does. carb is still in the air but 850 mighty demon was first choice only because i cant afford a 4150HP series 830. bottom end is strong. crower rods,srp pistons and stock crank 10 under. 700R4 trans with a non lockup 3000 converter. flashed at 3000 with the previous 400 motor and about 3400 on the 125 shot i ran last yr and thats the max i will be using this yr also. 71 grand prix wieghed 4000 out of gas. 12 bolt with 390 which i planned to reduce to 342s. and im sure the converter wont be quite right but im gonna try it first. the cam me and jeff kaufmann liked was the crower 247/252 at 50 and 505/517 lift on a 112LSA. i like the 112 for the nitrous and also overdrive trans and heavy car. tell me what you think but i was pretty convinced from what kauffman explained to me about a nice flat torque curve and street ability especially since without milling my heads alot im only getting 9.3 to 1 comp. my heads cc'd at 99. they're 6x4s but were high for some reason. also zero deck. thanks - scott

[pro-tour79]

I see no one is talking about the fact that the engine is an air pump and the stroke and rod length have a lot to do with this too, TYPICALY a 455 can use a single pattern camor more int. duration because of the fast but short piston speed duration from TDC so you need to max your int., look at the BBC short R/S ratio and from the factory they came with big int. ports 1.7 rockers.
Now the 400 has a much better R/S ratio but needs all the help it can get from the exhaust side and you will have to watch you overlap to avoid reversion.