Thread: carb size ?

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any of you guys remember what size 4bbl. carb was on the 350 rocket motors in the 68-72 cutlass. i've got a 600cfm edelbrock but i think thats going to run to rich

795 cfm Q-jet....I have had plenty of the old rockets....

if mine had a 2bbl do i have to change the cam. thanks

All rocket motors cam with a four barrel carb....

And No you do not.....On an Oldsmobile you can tell if you have a rocket motor under normal running conditions with a timing light...

Standard V8's had 8degrees initial while the rocket motors had 16 degrees initial.... The cams were advanced 4 degrees ( 8 crankshaft degrees) for more off the line low end grunt....

Now you know

Originally posted by dr_bowtie
All rocket motors cam with a four barrel carb....

And No you do not.....On an Oldsmobile you can tell if you have a rocket motor under normal running conditions with a timing light...

Standard V8's had 8degrees initial while the rocket motors had 16 degrees initial.... The cams were advanced 4 degrees ( 8 crankshaft degrees) for more off the line low end grunt....

Now you know

i guess I'm a little confused. How are you able to check cam phasing with a timing light? The position of the advance or retard of the cam in relation to the crank has nothing to do with ignition timing.

yep...zactly what tech said, valve timing is checked with a degree wheel. ignition timing is checked with a timing light.

Try this at home.....

Set a cam "straight-Up" set the initial timing at 8degrees BTDC....

now pull the front cover....degree the cam 4 degree advance....put it all back together....run the engine....

Now read the timing light....Notice I did NOT mention touching the distributor.... cause I did NOT....

The timing light WILL read 16 degrees BTDC.... bet you a Dollar....

The cam is fased with the distributor in this situation.... we moved the timing in relation to the crankshaft.....

Some will argue when you adavnce a cam you have to reset total time you have to bump it back 8 degrees....

Oldsmobile would argue in it's day the fact that the more you advance a cam the more total it can handle.....

Also running a cam "straight-up" you will be lucky to get the initial timing up to 16 degrees and it will still start most time it wont.... It will drag hell out of the starter/ kill the battery

Advance it 4 and initial at 16 it will crank easy as pie.....I have rebuilt umptine Olds motors...Tis how I know....

Same theory works on any engine you can adjust the cam without pulling the distributor....

Do you supose thats why in computorised vehicles the General may run as much as 55-60 degrees total

Any debate?

Debate?, yeah I'll debate ya on this, but right now I'm late for a Mother's Day function. Check back later today.

well i'm confused on the "all rockets caim with four barrels" statement, my 70 cutlass is an unmolested cutlass s with an olds 350 with the air cleaner that says rocket 350 and theres a two bbl on it. i know it hasn't been changed cause my father did all her matainance since she bought it. ?

thanks if that don't clear it up nothin will i would have to sa that is the most informative link i had ever seen thanks a ton

O.K., school's in session....

"Set a cam "straight-Up" set the initial timing at 8degrees BTDC.."

O.K., the crank gear is installed on the crank in the zero position, neither on an advance groove nor a retard groove and the cam is installed on the marks with no offset dowel.

"now pull the front cover....degree the cam 4 degree advance....put it all back together....run the engine...."

O.K.

"Now read the timing light....Notice I did NOT mention touching the distributor.... cause I did NOT...."

O.K.

"The timing light WILL read 16 degrees BTDC.... bet you a Dollar...."

You bet it will, because when you turned the cam in the direction of rotation, you also turned the integral rotor drive cam gear which is engaged into the distributor rotor shaft gear, thus advancing ignition timing at the same time you were advancing cam timing.

"The cam is fased with the distributor in this situation.... we moved the timing in relation to the crankshaft"

Yep, the cam is always phased with the distributor rotor because the cam gear drives the distributor rotor gear and we did indeed advance the ignition timing in relation to the crank. No argument.

"Some will argue when you adavnce a cam you have to reset total time you have to bump it back 8 degrees...."

Yep, some guys are funny that way. If I had my ignition timing optimized, I wouldn't want to add any advance to it either.

"Oldsmobile would argue in it's day the fact that the more you advance a cam the more total it can handle....."

I can't speak for Oldsmobile, but as for myself, If I advance a cam and move the intake closing point to earlier in the valve event, I'm going to make more cylinder pressure and therefore might be looking at taking a little timing out of the motor if I was marginal on pump gas in the first place.

"Also running a cam "straight-up" you will be lucky to get the initial timing up to 16 degrees and it will still start most time it wont.... It will drag hell out of the starter/ kill the battery"

This is where you're starting to lose me. Initial ignition timing is set with rotation of the distributor housing and a timing light on the harmonic damper. You can dial in any ignition lead you want, no matter where the cam is in relation to the crank.

"Advance it 4 and initial at 16 it will crank easy as pie.....I have rebuilt umptine Olds motors...Tis how I know...."

Now I'm starting to get the picture of what you've been doing. When you advance a cam, it's easy to fake yourself out and move the cam sprocket clockwise instead of moving the cam clockwise.

"Same theory works on any engine you can adjust the cam without pulling the distributor...."

Yes, of course you can adjust the cam phasing without pulling the distributor.

"Do you supose thats why in computorised vehicles the General may run as much as 55-60 degrees total"

I suspect that if a motor can tolerate that much ignition timing, it's under a no-load situation or very light load. I've seen fellows run 50 degrees total on a SBC under light cruise conditions and that's on a non-computerized carbureted motor. The motors that are controlled by an ECM would probably be able to tolerate 55-60 total, because the computer could pull the lead back to reality in a nanosecond the very instant the motor saw some load.

bump

Good debate..

Yes, of course you can adjust the cam phasing without pulling the distributor. If you're saying you can adjust cam phasing by changing ignition timing, you're sillier than I have given you credit for.
..

No that not what I am saying...Moving the ignition has noting to do with cam timing....

Only way to do that is by moving the cam position itself in relation to the crank...

I do know how to advance and retard a cam and it's relationship to the power curve and all it has to do with anything....

I do know that the mid 70's Olds v8's were some as follows

what they considered rocket had the timing on the sticker also as 16 deg BTDC @ 650-800rpm

Non-rockets were 8deg BTDC

Although I am not sure is how the production cams were advanced.... I think they were like early fords?

They advance was built into the gear set , usually the bottom gear?

Denny.... that is some good info.....back in my day I worked at a shop that the owners redid all kinds of Olds from 40's thru 80's these guys were really slick on Olds engines...They really had some neet factory race stuff....

I'll have to admit....

I do like to add a little fuel to the fire! I was alway taught by my mentor " you have to think outside the box!". His thinking was if you always thought inside the margins you are only going to be like everyone else... True I think....

My first lesson was on camshafts and advancing/retarding for my second application ( 1974 chevy 1-ton van w/4:10 rear gears)

I bought that van and it was a california van that died in Indiana. I got it with a spun bearing, so I decided to build a new motor.

first we had to decide compression and for efficiency I chose flat tops Hyperutectics @ 9.4: and they came in @ 9.62:1

Then when I asked him how to choose the cam the lesson was on... He told me and smiled and said use the 327 350hp then, he asked me why he chose that? I didn't know

He also told me that cam are and will always be a mystery to alot of people especially to those who don't understand them and it was my time to learn....

He made me go and plot a power and torque curve of the rated power and then we got into advancing and retarding and it's effects on the power curve...

Basically when you advance a cam you bring the power curve in earlier and retarding brings it in later...

Next we tested... I did the motor with the cam straight up and drove the van 1/4 mile....disapointed with my choices I drove back to the shop and moaned how such a turd the van was....He laughed....

He told me to pull the cover and degree in 4 deg advance and put it back together and NOT touch the ignition timing. So I did.

This made a huge difference... I cannot say how much but it did.
Next after that he told me to pull it down again and dial in 4 more degrees and not shift it any higher than 5,000rpm?

When I was done I was amazed at the difference this engine has made just by moving the cam around but, that wasn't the hole lesson... when I was done I ended up with a 1-ton van that made a few pases with the best of 13.02@ 92mph in the 1/4

Now after that he told me max advance on that cam was 13 degrees advance ( camshaft advance) and that at that it wouldn't rev much over 4,000... So I tried the theory and this combo will absolutly rocket out of the hole but does not like full throttle....

Every motor we have done like this will flat walk away from just about everything at part throttle.....

My second lesson was to learn how to use the " time factor" meaning figure out how much time you need/have to do what you want then build the engine to run just inside that window..

My mento is a great person/ ex-racer and he ran a 58 vette back in the 60's with a 283 naturally aspirated and was running 8's

Most of his engines get banned from local tracks (roundy-round) and he has the only ford 4 bangger round here running in the 9's

He's the main reason I really got into 283' so much... and now big inch smblk.

dr, thanks for sharing your experience with cam advance/retard. I've never advanced a cam as much as 13 degrees, I think 8 was the most I ever went and even then, I was checking intake valve to piston clearance real close. My experience has been the same, the more advance, the more it'll pull like Jack The Bear on the bottom, while giving up more on the top.

Here's a chart for the guys who have never done this, showing the consequences at the bottom of the page:

http://www.co.jyu.fi/~rax/lobe.htm