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Discussion Starter #1
JonT,
you beat me with your question by a day! I was gonna ask someone to run my bb(402) through the desktop dyno to compare hp/torque figures on two cams that im having a hard time choosing between. if someone could run this on their program then help me figure out which would be better suited to my application it would really help me out. first the specs on the car:

.030 over 396 (402) with stock pistons
stock open (119cc) oval port heads
3 angle valve job (2.19/1.88) with cleanup of intake, exhaust runners
stock rockers
Performer RPM intake manifold
holley 750 vacuum secondaries
hei + msd 6a box
1 5/8 primary headers, 3in collectors, 2.5 in dual exhaust

ok. here's the situation. ive been looking for a cam to replace the 30 year old one thats in it now. ive settled on either the comp cams Xtreme energy 268 with specs as follows:
LIFT .515/.520

DURATION AT .050 224/230
LOBELIFT .3030/.3063 LSA 110

or the Xtreme energy 262 grind that jonT described:
LIFT:.504/.510
DURATION AT .050 218/224
LOBE LIFT .297/.300
LSA 110

ok, the technical part was easy, just plug into desktop dyno (which i wish i had) and find the numbers. now for the fun of the application part - it's intended to be a street driven beast that i can flog, but consistency is the key as i have to drive it to school everyday. i was hoping that with the weight of the car (guessing about 3300#) and the rest of the drivetrain (12 bolt 3.08:1 behind TH400, saturday night special torque converter) that some of you more experienced engine building guys could decide which would be the right cam for me; i dont want to over cam the thing and ruin all my efforts. i was also tossing around the idea of pump-up lifters with the XE268 grind to give me the vacuum for my power brakes and a little less lift for some more torque off the line.
ive been comparing all the posibilities on this engine and this is the last decision i have to make before it all goes together. i wanted your expert opinions before i went and built a dud motor, so im hoping that you guys can help me out like you always do. thanks in advance! (repeat) (repeat)

john mason
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Discussion Starter #2
perhaps this is in the wrong forum, i just thought that more people would be able to see it and offer some input if in General Tech. If anyone could help me out i would really appreciate it. thanks.

john
 

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penguinjohn - I obviously don't have a dyno but I bet you'd be better off with the 268. You've got the large valves in your heads and you're running larger exhaust than me (2 1/2"). Plus you've got good spark for the higher rpms.

I've wondered myself whether I should have gotten the 268 cam - it uses the same springs and it's not that radical a profile anyway. And I've heard that expression "You can't kill the torque of a big block" and know that I won't be able to put all of that torque to use.

Still...for a true streeter how many times do you need to take it past 5000 rpm? And mashing the throttle at 2500 rpm with 470+ ft. lbs. of torque has got to have me "cheesin'" for a week!!!

Good luck...You can't go wrong with either cam

------------------
'69 Restification
 

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Discussion Starter #4
JonT,

thanks for the reply. i was hoping that someone would run it through the dyno, as i would like to see where the actual powerband of the combo is so that i can choose an appropriate stall converter. like you said, i dont know how many times i will be taking it that far past 5000, and the 268's powerband (1600-5800) might be a little high for my application so i wanted to see the numbers before i went ahead and ordered it. Please, somebody run it through that magical program and offer me some advice. Please!!

john
 

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hi john,
i ran what your info through the program i have, but i took a stab at the compression ratio (9.5:1), and came up with 469hp with the 262xe, and 472hp with the 268xe. my dumb program doesn't tell me torque, but it will tell you the quarter mile, and everything else needed to drag race and setup the car.
i have the comp cams xe294h cam in my 408. have yet to fire it up, but i'm told it will work good for what i have and for what i need it for.
later,
bruce
 

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Discussion Starter #7
thanks for the reply bruce. what kind of stall converter will that engine be bolted to? i dont really understand all this flash point nonsense, but im looking at one with about a 2000 or so stall point. what are you running?
if anyone could find a torque for this combination (9.5:1 sounds about right on the compression) i would greatly appreciate it. thanks.

john
 

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Actually 112CC heads will yield around 9.6 to 9.7 to 1. I know because I cc'ed my heads and calculated the compression ratio.

Your heads will be closer to 9 to 1. I will run all this through some programs I have and I will get back to you tonite.
 

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Ok here's the deal with both CAMS:

RPM 268HP 268TQ 262HP 262TQ
2000 157 412 166 435
2500 203 427 212 445
3000 251 438 259 453
3500 301 451 308 462
4000 348 457* 352 463*
4500 391 457 390 456
5000 424 445 416 437
5500 437 417 423* 404
6000 438* 383 412 360
6500 418 338 382 309

*Indicates MAX values

As you can see there is not much difference and assuming a 2400 stall speed convertor 1/4 times on the 268 would be 13.3 @ 111.5 MPH. The 262 cam would yield a 13.4 @108 MPH.

I would suggest the 262 CAM while you may give up a little HP, you'll get more torque especially at lower RPM levels.

By the way, the valve timing events are VERY IMPORTANT when you do these calculations. I got these for you from the COMP CAMS website. They are usually expressed in terms of timing at .006.



[This message has been edited by sr71bb (edited 12-11-2000).]
 

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Discussion Starter #10
sr71bb,

thanks for the help. i was hoping that the 262 would turn out better torque without alot of hp sacrificed, thanks for confirming this. i didnt know about including the opening and closing points for the valves, i didnt realize that the program was that extensive. once again, thanks for the help.

john
 

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Discussion Starter #11
sr71bb,

is there a way to specify pump-up lifters like rhodes in that program? i was wondering if by using those with the 268 grind that i could salvage some low end torque and get the advantage of a higher hp figure. thanks.

john
 

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john,
i run a 3500 stall converter with that cam. a lot of people are probably thinking that the cam is too big for that size engine. in fact, the cam that cam out of the engine was actually bigger, and caused me some carb troubles. so the engine builder said i could run the cam, but i needed to spend 800.00 on a new carb, OR, spend 200.00 on a new cam. well what do you think i did ? i called comp cams and told them what i have, and they fixed me up with the 294xe cam. i can run this cam because i have 11.5:1 compression and they said that with that high compression, i can get away with it in that small of a big block. if you want to play around with the program i have, go to: www.martelbros.com and download a free copy of dragstrip plus. it's a fun program and from what i've been told, it's pretty accurate. that program can tell you what type of stall you should run. just plug in your info and have fun. but i would say a 2000-2500 stall should be good for what you have.
later,
bruce
 

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John,

There is no way to specify the "type" of hydralic lifter just the type of cam. I don't think though that the use of the pump up lifters would really make that much difference. I do like the rhoades lifters though.

[This message has been edited by sr71bb (edited 12-12-2000).]
 

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Discussion Starter #14
so other than added vacuum at idle, are there any other advantages to using pump-up lifters? i had assumed that by decreasing duration at low rpms that it would boost torque. is this true? thanks.

john
 
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