Thread: Cam question

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in the near future Im looking to put a thumpr cam kit into my 305 sbc (1983 camaro, stock heads, edelbrock intake, and 600 cfm carb 4b, shorty headers)

http://www.compperformancegroupstore...ory_Code=ThKFT

i have a few questions for this:
other than what is included in the kit, will i have to purchase anything else for the installation (other than lube) or make any adjustments?

also, the vacuum with this cam is low, so will an independant vacuum source be needed for power brakes and the carb/advance and such?

ive never experimented with cams before so i am in the dark here!

thanks for any help guys!!
keep 'er squealin!

sniper

Probably way more cam then a stock head 305 could ever use... If your car is an automatic, going to need a higher stall converter, too....

that might be over cam-ing your 305. you might want to step it down a few steps. if you had more cid to eat up some of that duration it would be ok. if you decided to go with it i did notice it had the valve stem o rings. where are the seals? if your going that far to changed valve springs repleace your intake and exhaust seals too. i ran a xe274 in one of my 355's. that was a a bit over cam-ed. try finding a cam with a bit less duration. lobe sep is going to be very choppy at 108. 110 is very noticable. just my opinion

This is a poser cam, for those who want to pretend that they have a performance motor without going through the drill to increase static compression ratio, set the squish and a myriad of other changes to actually build a performance motor. It's marketed to impress the geeks down at the Sonic Drive In who don't know any better.

With the intake valve closing at 35.5 degrees ABDC @ 0.050" tappet lift and guesstimating your static compression ratio at 8.00:1, the dynamic compression ratio with this cam will be 7.049:1 and the car will be slower than it was with the stock cam. But hey, you'll be posing and sounding cool.

Plan on investing in a looser torque converter like Dave said and a vacuum cannister for the brakes.

I just can't understand spending $600-$800 and going through all this trouble to go slower, but hey, whatever blows your skirt up!!

Here's a basic english explanation of what you can expect with that Thumpr Cam you are considering. It is gonna lope and jump like it's the meanest pig on earth. BUT- It will come off the line in the 1/4 like the engine is near stock. Then, about at the 1/8th she will come to life and pull hard. Now, if you re-consider a high lift, shorter duration, you will still get a great sound, but it starts to bring the bottom end of the spectrum to life, and you will see that it pulls hard all the way thru. In my younger years, I had over cammed a Plymouth, and it turned out to be a dis-appointment that costed me cash. Now, I am a bit wiser on choices.

My suggestions would be more on the line of like a Lunati Voodoo # 60102 or if you want to put a stall in it, a 60103. Make sure with either one of these you run long slot rockers and the 60103 will need valve springs ( seeing one of the lift measurements is .504 ) to keep from binding. The 60102, I have seen run on stock springs ( I'd use better ) but, I have seen it done. The 60102 I believe will suit you better, given your engine statement above.

Also, after you change cams, start thinking about a double pumper carb. That helps alot too.

You're dealing with a fairly stock motor here. I'll assume it's the original 305 so probably 8.6:1 on the compression and I'd also assume that you've got a few miles on this motor. In all likelihood, the cam you're looking at would be a colossal waste of money. Without trying to sound harsh - what exactly are you looking to do? A bigger (than stock) cam is almost always a disaster unless it's part of a system, i.e., with the heads, perhaps new pistons, intake, headers, etc..

If you're dead set on a replacement cam, the Lunati 60100 is more along the lines of what you should look to for stock motor. It's 250/256 degree duration and .437/.454 lift is about all the stock heads will be able to handle and .454 lift may be too much for your springs (as mentioned above).

As to a double pumper - well, sounds cool to say you have one, but most people have no idea what the double pumper brings to the equation. The 600cfm you've got probably doesn't perform as well as the Q-jet that the 305's came with when optioned with a 4 barrel.

If you really want to have some grunt and snap, start this process from scratch. Sit down with a piece of paper and determine what you'd like to have in terms of horse power and torque. Then select the components and build the engine on paper - costing out the process. If you ask, there are several here who will be more than willing to help, but we tend to take the parochial approach and consider the engine in it's entire form and not just a piece here-and-there. Bolting on chrome valve covers or a chrome alternator is cool and fun, but a piece meal approach to the guts of the motor will just give you a lot of trouble.

I know it's sometimes hard to wait until you have the funds to do "the whole engine" but believe me - it's better to do it that way and far more rewarding as you'll have a quality end product. Delayed gratification is a lost concept these days and we tend to want to rush through every aspect of our lives - including our hot rodding. It's supposed to be fun, but we need to remember that the "demands of the services or the importance of the task are never so great that we can not take the time to do it right."

Just my two cents - but I've been where you are. Other will, I'm sure chime in..

Regards,
Glenn

Originally Posted by glennsexton

As to a double pumper - well, sounds cool to say you have one, but most people have no idea what the double pumper brings to the equation. The 600cfm you've got probably doesn't perform as well as the Q-jet that the 305's came with when optioned with a 4 barrel.

Glenn, thanks for your insightful and intelligent reply. If a guy will take a little time to read up on this stuff, he'll find that the carburetor manufacturers will recommend a vacuum-secondaries carb if you're using a converter that stalls under 3000 rpm's. Over 3000, a double pumper can be used to advantage. Agree with the Quadrajet, best 4-bbl carburetor ever designed.