Edelbrock 500 cfm vs 600 cfm

[4pilgrim4]

My pickup ride is a 78 Chev K10 350 4 bolt, 4 speed manual, 205 transfer case driving 3.73 : 1 axles. The carb is a Q-jet on top of an SP2P manifold with the divider removed. Fuel economy is good at 16 - 18 at 55 - 60 mph. The greatest use is towing a small 2500 lb fiberglass camping trailer.

The poor old Q-jet is really worn out, especially the throttle shaft holes. Min idle RPM is almost 1000.

Rather than re-bush the bores I'm considering a small 500 cfm Edelbrock or perhaps a mid size 600 cfm model as a replacement. Since I am not in the race crowd and my truck rarely sees 3000 rpm, my calculations indicate that a 500 cfm unit would be more than plenty. (I'm also aware of the engine size recommendations for the two carbs.)

Just wondering if someone has some experience in this area or knows of someone who does.

[Tx Firefighter]

I'd go with the 500 myself. You likely know this, but the SP2P was an intake Edelbrock made in the 70s designed for improving fuel economy. It was not made for performance improvements over the OEM intake. Those were the oil crunch years and folks were feeling the gas prices so Edelbrock made these to try and offer improvements on the economy side. For this reason, the design uses very small (but efficient) ports. For that reason, I'd choose the 500 cfm unit.

[bowtiecb]

edelbrock leaks like *****. when my truck sits over night, i have to pour gas in it to crank, or even an hour it leaks into the intake, im going back to a holley

[thrive87]

Well I have a 600 and a 2 bolt 350 crate motor and have had no problem with it and i do pretty damn good on gas well if im not smoking my tires

[rayfinseats]

I bet the return spring on that Qjet is pulling back and not forward? That wears out the throttle shaft.
I'd go with the 500 unless you run high RPM.

[3r!c84]

750 holley !!

[thrive87]

idk on just a stock 350 i mean a 4 bolt maybe but why...

[Tx Firefighter]

Originally Posted by bowtiecb

edelbrock leaks like *****. when my truck sits over night, i have to pour gas in it to crank, or even an hour it leaks into the intake, im going back to a holley

Fix it then and don't throw the baby out with the bath water. An Edelbrock carb has zero gaskets below the fuel level. All gaskets are above that. They are not prone to leaking for this reason. Something is wrong with yours. A Holley on the other hand has all gaskets subject to fuel. The float bowls, metering plate, metering block, and accelerator pump all are subject to leak due to this. I've had plenty of Holleys crack the accelerator pump diaphragm and dribble fuel all over the intake.

Originally Posted by 3r!c84

750 holley !!

On a heavy 4 wheel drive with standard trans and towing application a 750 Holley is no where near ideal.

Originally Posted by thrive87

idk on just a stock 350 i mean a 4 bolt maybe but why...

What does 2 or 4 bolt have to do with carburetion ?

[4pilgrim4]

Originally Posted by rayfinseats

I bet the return spring on that Qjet is pulling back and not forward? That wears out the throttle shaft.
I'd go with the 500 unless you run high RPM.

Yup!

And it appears that was the stock configuration from good ol' Generous Motors. I did change it so the spring pulls forward, but the damage was already done to the Q-Jet.

[4pilgrim4]

Originally Posted by Tx Firefighter

I'd go with the 500 myself. You likely know this, but the SP2P was an intake Edelbrock made in the 70s designed for improving fuel economy. It was not made for performance improvements over the OEM intake. Those were the oil crunch years and folks were feeling the gas prices so Edelbrock made these to try and offer improvements on the economy side. For this reason, the design uses very small (but efficient) ports. For that reason, I'd choose the 500 cfm unit.

I bought the SP2P back in the 70's and used it for awhile on a 72 GMC 4X4 4sp with 3.08 axles. With the 700-15 tires inflated up to max and easy driving I got gas mileage near 20. The big problem was pinging.

Now with this truck set up almost the same way pinging is almost no problem. I believe the cause of the earlier truck's problem was due to leaded gas. I pulled the heads and there was a thick crust on the combustion chamber and top of the pistons that was sort of peeling in places. I would guess these would glow with the heat causing pre-combustion. With unleaded gas the engine stays clean.

Anyway that's my story and I'm stickin' to it! :>)

My calcs also indicated a 500 cfm carb would be great. Thanks for the confirmation. Just doing a sanity check.

[thrive87]

I have used both and honestly 2 bolts honestly seem a lot stronger then 4 bolt mains cause from what i notice is that one of the bolts is on a weak part of the motor from what i saw at my buddies shop hes b lown so many motors from that specific spot but thats just me honestly if i have a stock 350 i would just stay no higher then a 650cfm no more just my opinion.

[Tx Firefighter]

4 bolt main blocks were standard in hi stress applications. They are stronger. I won't go into the aftermarket 4 bolt conversions as they are not relevant to this topic. Suffice to say that any application that GM felt might be abused enough to be a warranty concern, they spec'd a 4 bolt engine. Carburetion isn't relevant in that decision. RPM and engine load were the deciding factors.
Posted via Mobile Device

[thrive87]

I understand and thanks

[bowtiecb]

[QUOTE=Tx Firefighter;4395553]Fix it then and don't throw the baby out with the bath water. An Edelbrock carb has zero gaskets below the fuel level. All gaskets are above that. They are not prone to leaking for this reason. Something is wrong with yours. A Holley on the other hand has all gaskets subject to fuel. The float bowls, metering plate, metering block, and accelerator pump all are subject to leak due to this. I've had plenty of Holleys crack the accelerator pump diaphragm and dribble fuel all over the intake.



thats y i was go trash it, figured sense there are no gaskets below the fuel, i figured it had a crack in it, ik the jets are in the floor of the carb.thought it may b cracked in that area

[Tx Firefighter]

If you're serious about junking it I'd pay the shipping and for your trouble. I like to fix things.
Posted via Mobile Device