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Discussion Starter · #1 ·
hoping to have a civil discussion.

this topic has come up alot lately, and i gotta admit, back a few years ago, corral members were not as open to the idea, small port heads need a bigger cam, and large port heads need a smaller cam......... of course this is highly generalized.....



example.....

mild ported p head, wants 300 rwhp. lets assume intake, and exhuast are optimized for this. would require a fairly stout cam, with a fairly tight lsa to achieve this goal, no??

other...... vic jr head, supporting intake, and exhuast, wants 300rwhp. cam would be small, lsa would be wide, powerband theoretically would be broader?


what would the drivability differences be? torque peaks? this is a 302/306 for the street. pump gas, hyd roller cam, because thats what people here (myself included) are used to.


anyone have thoughts? like to hear from buddy, jay, ed (doubtful tho), chris, brian (if he is still around) and anyone else with a thought about it.
 

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the cam has to take advantage of the low lift and flow .....and overlap duration has to be correct to retain cylinder pressure or the net power will be down.
 

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have you ever heard some engine combo's allways have that funny pop just after the hit and then run real good above that....?
 

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Discussion Starter · #4 ·
actually, yes. "ram tuning" ??????


and again, which car is more drivable on the street? since gas is near 3 bux a gallong near me, what about the better milage? i would assume both @ 10:1 for 91 freindly fuel.........
 

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I wil let you know my thoughts in about 5 months when i finish putting mine together. :p

i am building a 302 stock short block and stock cam with a set of motorsport n heads(10 degree valve angle)that are over 200cc;s and a chamber size under 53cc's.the intake is a ported rpm2 with a set of 1 3/4 long tubes,3'' to x pipe then 2 1/2 exhaust.75mm race tbody and 80 mm maf.car is a 5spd coupe that will have a 4.10 and weigh under 3100lbs with me in it.

overall i tend to favor a slightly bigger head but on almost all my setups my cars dont weigh much and i tend to run a fairly steep gear.
 

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Discussion Starter · #6 ·
exact type of setup i wanted to compare.


my thoughts were, that the small port, large cam 300hp engine would be a narrower powerband, poor idle, poor milage setup. but then again, the small runner may help with the vacuum at idle, and low rpm bucking... i dont wanna spin to the moon, but i want a broad powerband, good idle, and potential for massive power down the road without having to purchase new heads.

anyway, thought there might be a little more input on my original question, is everyone avoiding this??
 

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I ran a p headed setup with a f cam that went high 11's.ran great but drivability wasnt perfect for tip in between 1500 and 2000 rpm then on my 347 i ran quite a bit of cam(240 at .050)and tip in at that rpm was bad also.

this time i want something that will idle like stock and still go mid 11's........i am sure it will do it.

i remmember about 15 years ago when i used to mess with clevelands alot that when we started mellowing the cams out they would run the same or faster in some cases and we would get alot of drivability back.of course we are jut talking about street car setups.in a light race car i might take a diffrent approach.
 

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ROG30Y said:
I wil let you know my thoughts in about 5 months when i finish putting mine together. :p

i am building a 302 stock short block and stock cam with a set of motorsport n heads(10 degree valve angle)that are over 200cc;s and a chamber size under 53cc's.the intake is a ported rpm2 with a set of 1 3/4 long tubes,3'' to x pipe then 2 1/2 exhaust.75mm race tbody and 80 mm maf.car is a 5spd coupe that will have a 4.10 and weigh under 3100lbs with me in it.

overall i tend to favor a slightly bigger head but on almost all my setups my cars dont weigh much and i tend to run a fairly steep gear.
Sounds bitchin'!

Now hurry up, :D
 

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ROG30Y said:
i remmember about 15 years ago when i used to mess with clevelands alot that when we started mellowing the cams out they would run the same or faster in some cases and we would get alot of drivability back.of course we are jut talking about street car setups
Exactly. Bigger heads. Milder cam. More driveabilty. More power.

Airflow = Power. A 300cfm head or a 250cfm head. Which one will make more power I wonder?

ROG30Y said:
i am building a 302 stock short block and stock cam with a set of motorsport n heads(10 degree valve angle)that are over 200cc;s and a chamber size under 53cc's.the intake is a ported rpm2 with a set of 1 3/4 long tubes,3'' to x pipe then 2 1/2 exhaust.75mm race tbody and 80 mm maf.car is a 5spd coupe that will have a 4.10 and weigh under 3100lbs with me in it.
This will haul a$$.
 

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The most flow you can get from a reasonable cross section of head is the ideal head for a combination. 6" openings... will lose the curve as bad as a small head.

When a small port head is used and the cam is designed in long duration to crutch the combination, the cylinder pressure bleed at low RPM will eliminat that high velocity "charge advantage".

The smaller the cam duration you can use to achieve the RPM window you want the broader the power curve of the engine.
 

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stock cam

I like the big head small cam theory its different and sounds like it will produce a more streetable combo.I am also going to test this theory but I dont think my heads are big enough but I am limited on head choices due to the 86 pistons.The combo I am going to run is stock 86 shortblock twisted wedge heads,spyder intake,75mm tb,15/8 long tubes,and the stock cam with 1.72 rockers through a t 5 and 4.10s. I am considering opening up the heads .Jay what ya think?I have read before its not the actual size its the cross section that matters.I love the idea of a stock idling car with a smooth powerband.
 

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IT really has nothing to do with theories and streetability and shifting torque...yada.

It is a function of displaced cylinder volume at the given rpms, and how big the door is entering or leaving the cylinder. Plain and simple for a given amount of displaced volume, the larger the door, the smaller the overall time is needed to move the displaced into or out of the cylinder. Throw in some lag issues and some dynamic stuff and thats the major part of it. Not a lot of subjectivity to it.

On a restricted flow motor you will need a lot of valve activity to fill the cylinder, but you cant extend the seat events too far or you loose the ability to generate good cylinder pressure due to late of an intake closing, paired up with over extending the usbale flow cross-section of the inlet path. so you will see real high ramp rates. as in the 2 barrel restricted oval track stuff, or stock eliminator type set-ups. On large crosssection inlets and or exhaust, for a given CID and rpm, you will need less overall time for the cylinder to fill or expell.

But you cant group it into particulars, you have to view it from the standpoint of IO,IC, EO, EC. this is the precise reason that valve events (cams) are so personalized to the particular combo and why global associativities of duration and LSA are pretty much meaningless. unless all motors in existences had same bottom end geometry, same rpms, same inlet and exhaust parameters.

Engine talk always centers around the numbers, but really everything is happening in units of time. ITs all flow. Displaced volume over a unit of time, is guess what? Cubic feet per minute, We see that term all the time. The only problem is, it is normally associated at the inlet or exhaust path, as opposed the cylinder volume itself.

I offer my valve timing chart as a decent exercise for looking at this topic. Its the closest I could come without math and without a big detailed write-up. the math is too critical to me and how much time I spent on this.

http://wighat.com/fcr3/timing.htm, then check out the chart. you may have to copy it out of your browser to your desktop or print it.

buddy rawls
 

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buddy rawls said:
But you cant group it into particulars, you have to view it from the standpoint of IO,IC, EO, EC. this is the precise reason that valve events (cams) are so personalized to the particular combo and why global associativities of duration and LSA are pretty much meaningless. unless all motors in existences had same bottom end geometry, same rpms, same inlet and exhaust parameters
Exactly.

I first calculate how much Lobe Area I am going to need for a given application. I then back into the IO, IC, EO, & EC. The intake center, exhaust are a by product of proper events. LSA is a by product of proper lobe centers. Thus when someone says "What LSA"? That is meaningless. Look at it this way. 2 + 2 = 4 everyday. In this elementary example the (2)'s are the IC & EC and 4 is the LSA. The number 4 is the product of 2 + 2. But if I say "4", how many DIFFERENT ways can I get to "4"? Infinate.

This is why I take 2 to 3 hours to do it right. And to date no 2 cams are exactly the same. Do I have particular lobes I am partial to? Yes. Do I use previous cams to get a foundation started? Yes. But I think it is hilarious when guys say they have a *custom* cam then a few days later another fellow says the same thing. But it is the same cam.......WTF? How custom is that? And what makes it custom? Just because it does not appear in a catalog its *custom*?

I have made this post on other forums. In 1991 I had a 100% stock block. I flycut the pistons in the block with a dremel in the driveway. I used TFS Street Heats that were 205cc (2.02 X 1.60). At 600" lift they went 305/210 cfm. I used a Wolverine WG 1087 with 1.7's. 222/232 542/567 w/1.7's 112 LSA with a 107 IC. I had 10:1 compression. 1 3/4 Motorsport J-302 Headers. 3" exhaust. A TFS Truck intake that utilized dual 54mm TB's off of a 460 EFI truck. The first Pro-M EVER made and it was 24# injectors. A FMS 110lph pump (the biggest that there was). A stock T5. 100% stock suspension plus Lakewood slapper bars. 4.10 gears. 26 X 10 slicks. Nothing, absolutely NOTHING by todays terms. The car weighed 3280 with me in it. It was the ONLY car my wife and I owned. Thus, we drive it EVERYWHERE! AC, PS, PW, CD player, it was all there. I went 11.471 at 117.1! By the math that is over 400 RWHP! Guess where I shifted and it went the quickest? 5800 RPM and it crossed at 6300 RPM. I had a computer (Crane Interceptor prototype that was given to me by Doug & Mike Wallace) that allowed me to shift higher. I did. I shifted at 7000 RPM because I could. I went 12.30's right off the bat after I had went 11.60's with a stock computer. Thus, I began to short shift. The faster and faster I went as I short shifted. I ended up at 5800 RPM. Now I do not feel that the WG1087 was even near optimum, but back then there was only 3 cams available and *custom* was a Taboo word. The same combination today would be very close to a 10 sec timeslip because of the parts available.

205cc S/H's at 5800 RPM with a 3" stroke at 5800 RPM. Go figure.......
 

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Jay, you and Buddy are going to have people tring Yates heads on stock bottomends. LOL! Don't give it all away you two. Jay, you ever find someone wanting to do the Vic Sr headed 302-306??? Good info.

Later, Greg
 

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Okay, Buddy and Jay, going backwards then, for your average 3200lb stock-shortblock (cam included) stick car with 3.73s, what is the optimum intake runner volume for peak power at about 5800 rpm? That would be beneficial info for everyone, and also what intake runner length would work best with these? Thanks for your inputs....
 

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Discussion Starter · #17 ·
i get what your saying on the io/ic/eo/ec being specced otimum, and thus the adv duration, @ .200, and .050, and lsa fall where they may. pick the valve events, pick the lobe you want to use to get it there, and viola.
fact remains, to simplify, you have to use comparable numbers that guys are used to....


so, once again, is the 3200lb 300rwhp small cross section motor going to be more "streetable" than the 300hp large cross section motor, in the same car, with the valve events optimised to take advantage of the setup?


thanks for the excellent input thus far.




fwiw, want to know if i should get a set of vic jr's, afr 165's, tw, afr 205's, tfs sh, or a tfs r for my relativly mild 6200 rpm limit, AUTOMATC 100 mile per day, dailey driver. that one day may, or may not get a 15lb assist in the form of a vortech, novi.........or whatever the flavor of the week is in a year or three.
 

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Everything has limits but in general I like to a go a little bigger than some people on heads and then run a smaller duration cam in it as well just so that the customer has the option of more later but you can go too big in my opinion absolutely. OTOH I seriously see this more with the 306 type stuff than anything else. It's harder to get too big on the larger Windsor stroker stuff.
 

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hmmm guess my 165's on the 364 will be junk...I better sell them off!!! :shakehead
 

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MAT88GT said:
hmmm guess my 165's on the 364 will be junk...I better sell them off!!! :shakehead
It depends on what you want. If you are looking for really big power then yes the 165s are way small. If you have an efi longrunner deal that's not gonna make a lot of power anyway they will give you more area under the curve possibly but even then I think the 185s would be better to start with probably.
 
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