84firebird

hey, I'm looking for a cam for my 355, and I was wondering what you all thought. specs are...

-1973 350 block bored .030 over
-1970 LT-1 heads (487 casting number) opened up to 2.02 and 1.60 inch SS valves, polished ports, Milled down .020, cast guides
-9.3:1 compression ratio with heads, alluminum hypereutectic pistons
-Weiand High Rise intake
-Mallory $170 distributor, with the high output coil
-MSD Super Conductor Wires
-Accel Header Plug spark plugs
-Shorty Headers, and custom dual exhaust all the way back
-holley 4160 series carb, 3310 750 cfm vacuum secondaries (yea I have the quick change secondary spirng setup) also have .110 needle seat assemblies
-Holley 85 gph mech fuel pump
-Melling high volume oil pump
-electric radiator fans

tranny is a turbo 350, with a B&M shiftkit, and ratchet shifter, stock stall torque converter

for my current cam and rockers

222/222* @.050" .447/.447" lift w/ 1.5 ratio rockers... it's the 327/350hp camshaft i think it's cut on a 114*

I was looking at the comp cams XE 284 cam
Grind Number: CS XE284H-10
Valve Lift with Factory Rocker Arm Ratio: 0.507 int./0.510 exh. lift
Advertised Duration: 284 int./296 exh.
Duration at 050 inch Lift: 240 int./246 exh.
Basic Operating RPM Range: 2,300-6,500 RPM

http://store.summitracing.com/defaul...=KeywordSearch

Now I can change the torque converter if necessary but I dont want to go over a 2500 stall, if i need more compression I will drop the head gasket down to .015" thick gaskets from the .039"

but I was curious about what you all thought about the combo? an extremely similar combo was built with the same compression carb intake heads (kinda my heads have bigger valves) exhaust etc. just had the original LT-1 cam and it hit 376hp thing is with the lt1 cam i'd need the corvette's 3000 stall, which is a bit high for my driving. however I would like at the least 350hp out of it, and btw it's in my 84 firebird.

Thanks for your input

angel71rs

Your current cam is seriously outdated. very lazy ramps resulting in a lot of overlap. So a modern cam would help a lot. But I think the XE284 is too big. By the time a 240* cam starts to come on upstairs, say > 5k, the heads are starting to sign off. So you will lose a lot of bottom end torque, and gain not much at high rpm cause those heads will choke things off.

Better something around 222 - 224* if you want to stay around 2500 stall with moderate (3.42, 3.73) gears. Just going with a modern design will give you more hp with no loss of low end torque. I remember reading a dyno test that compared the L79 cam to a modern cam of comparable duration @ .050. The modern cam made ~ 25-30 more hp... and better low end torque.

If you want to go with the big cam, you will need to match it with more stall, at least 4.11 gears, and better heads.

84firebird

hey thanks for the input, I actually found another cam that I like now after considering your thoughts, lunati bracket master II (LUN-00010LK at summitracing.com)

the operating rpm range actually starts 200 rpm lower than my current cam, and lasts 800 rpm longer. and in the part description they say it has a very lopey idle, which as you all know, is just sexy

Cam Style: Hydraulic flat tappet
Basic Operating RPM Range: 2,000-6,000 RPM
Duration at 050 inch Lift: 230 int./230 exh.
Advertised Duration: 292 int./292 exh.
Valve Lift with Factory Rocker Arm Ratio: 0.480 int./0.480 exh. lift
Lobe Separation (degrees): 109

IHI

I ran that exact lunati in my old 355, 9.3:1, etc...ran a best of 12.74 but my heads were killing me so it had more in it. Very nice consistnt cam though. I ran a 3500 stall behind it and was averaging 1.72-1.74 60's with my 27" tire and 3.73 gears. One thing I found is it liked the vic jr with 1" 4 hole spacer ALOT better than the rpm air gap that seemed to peter out about 5500 rpm, with the installation of the vic it pulled strongly into the 6-6400 range.

Aside from all that, a quick convertor talk. Just because it's rated at 3500 does not mean you will not move until 3500 rpm, WAAAYYY to much confusion with convertors in teh world and how they acutally work. Sure if you ran a 8" 3500 it's gonna be very loose and will stall higher in typical street driving mode casuing excessive heat and shortened trany life. get a 10" 3500 like I had and it drives no differently than what your used to now...wanna know the difference...the 3500 will FLASH higher and reach the "3500rpm" point from a dead stop to WOT condition and hold there until car speed catches up with drivetrain speed-about as easy as I can describe it, and once everything gets to the same speed the tach will start to rise again. All stalls are advertised at a certain rpm range, this DOES NOT mean you can foot brake it to that rated rpm...if the convertor is build right you will overpower your mechanical brake system far sooner than you'll hit your flash point.

I could give a quick link for more in depth convertor discussion if you want, but dont be afraid of higher advertised stall rating becasue you think they're not streetable. I currently run a advertised TCI 4600 stall that ACTUALLY flashes to 5K on the hit...in day to day stoplight traffic it's no different than any stock convertor I ever drove in a daily driver and the best part is tranny temp guage stays stuck on 120* 90% of the time and may reach 180* after a 1/4mi pass.

Matching the convertor to the cam is ESSENTIAL to running hard, convertors are 3rd on my priority list for going fast effeicently with heads/cam being #1 and #2. A rough ruld of thumb for proper convertor stall speed-take the 2nd number in the actual duration and that is the range you should be in. EX: 240 duration should put you roughly in a 4K stall speed range, 230 in a 3K stall speed range, etc...very general, but give you an idea of where you need to be.

HeavyChevySS

Great informative post !!!

84firebird

IHI, I can't thank you enough for that info. And I think I speak for most when I say that "our IQ's have raised significantly (atleast 15 points), for having read your post"

I always thought that you needed to hit that rated rpm and hold it or you'd burn the tranny up.

So 12.74 with that cam..... I'm diggin that, I'm thinking I'll back it with either 3.73s or 4.11s I'll have to run the numbers to make sure my 3 spd will allow me to drive on the highway at atleast 60 with the 4.11s otherwise 3.73s

but i was just thinking, you said matching the converter is essential, I was wondering if higher gear ratios would help adjust that somewhat too? if so then how much?

lol I still find a question to ask, hey you're a life saver man, woulda probably ordered up a small stall for fear of not being able to drive down the street, and then it'd be an 8" (knowing my luck) and I'd burn it up anyway

Thanks Again

IHI

Depending on flow numbers for your heads surpassing my 12.74 should be an easy feat since all I had were stock 305 heads with 2.02/1.60's...not an effeicent flowing design by any means and severe valve shrouding to really hinder flow, but they served the low buck purpose back then. If your heads are flowing well and you want to go a little faster, stick with the 3500 stall range but jump upto the next brk mstr II with the .515" lift. This cam powered 3 very low buck street cars at our track into the low 12" range N/A and 1 got high 10's on juice in the cool fall air. Still streetable, but really has the nice lumpity lump at idle. The .480 your looking at is also very lumpy and gets attention, but the quicker ET for the same price on the cam is worth noting as long as you get the gear to match it. If going with the bigger of the 2 cams mentioned, stick with the 4.10/4.11 gear set since it likes to breath in the mid to upper rpm range.

When I ran my TH350/3500 stall and 3.73 gear with the .480 cam I was only trapping 55-5600 rpm at the big end using the rpm air gap intake. typically if all you change is from the 3.73 to the 4.11 it's only worth about 500rpm give or take a few hundred so at the strip with 4.11's you looking to cross around 6K which IMO is the cut off for a long term relationship with any motor...motor in my sig was shifted at 6K, even though it'd pick up a few hundreths taking it to 7K...but it's not worth it IMO...plus it's always good to not show all your cards bracket racing so if you feel it spin you've got pwr in reserve to "catch up" and that saved my azz a few times.

As far as street driving, nothing beats low gears for smile factor. Expect to run around 3500rpm at 60mph with a 27"/28" tall tire out back with 4.11 gearing. So long as the cooling system is upto task and you have good parts in the valvetrain it wont break a sweat for years to come, I ran mine 2 years before upgrading to the 388. IMO I'd rather run a 28" tall tire for a larger contact area should you goto the track...more contact area with a taller tire than a wider tire because of increased roll out, not to mention you'll open up a rpm window since it wont trap as high and lower hwy rpm as well.

Either cam mentioned is streetable, sound killer, and run great to boot. Just a matter of putting the other parts in place to work with it.