As the title says...what criteria would you need to fulfill in order to support 750 cfm on a 355? I have an Edelbrock 1405 ("mild performace" calibrated) and a 1406 ("economy" calibrated). I have been told by a couple of friends the 1406 isn't enough for my motor, even when I changed the rods and jets near the max. it can accept. I am probably going to drop the 1405 on and start tweaking it to see if I can get more out of it. It occured to me to look at the Edelbrock recommendations for the 1407 (750 cfm) to see whether it's even a candidate. It wasn't all that specific and I thought I could get more info from the guys that have probably tried all the possible combinations out there! ;)

Here is one.. a 355 with 270 comp and ported 186 heads built to rev. (LOOSE).. liked the 750 afb better than the 625 afb...and they were jetted and tweaked ....then slapped on a 3310 that was jetted and set up...the 750 afb had 300rpm more on the top than the 625 and produced 1/2 mpg more...the 3310 would not hold a candle to either afb..

so i removed the air horn and polished the venturies ..thinned the throttle shafts and added smaller screws ....then back to the tuning and i got it to run identicle to the 750afb...now i run 2 600cfm eddys on a 355 with a very tall tunnel-ram tr1yx

An engine only pulls what it needs you just have to get the mixture right....the more r's you turn the more cfm it will need...

mine are 7000+ rpm

I have run a 3310 on a mild 350 before using the purple secondary spring. Worked mint with a mild stall and 3.42 gears in an 82 Trans Am.

The 1405 and the 1406 are the same carb. Yes the 1406 stock calibration is for better economy, but other than that they are identical. If you check the specs on the Edelbrock website you can changed the metering rods, jets, and step up springs to have the same specs as the 1405. If you could borrow a 3310 (750 Vacuum Secondaries) or a 770 Street Avenger you will be pleasantly surprised.


Dave

Something a lot of people don't know, or have forgotten, the 302 Z/28 engines ALL came stock with a 780 Holley. Screamers!
(it was rated 780, although, I think they were more like 750)

The 1405 and the 1406 are the same carb. Yes the 1406 stock calibration is for better economy, but other than that they are identical. If you check the specs on the Edelbrock website you can changed the metering rods, jets, and step up springs to have the same specs as the 1405. If you could borrow a 3310 (750 Vacuum Secondaries) or a 770 Street Avenger you will be pleasantly surprised.


Dave

I actually have a friend who says he's got a 3310 in the garage that he's going to clean up and send to me. To this point I have only played with the Performer series and I am very comfortable with them. What would need to be changed as far as the connections (vacuum, throttle cable, return spring) in order to switch over and try a Holley?

On a Holley, they just have one big Vacuum fitting for PCV/Power brakes, its on the back. Your Edelbrock has 2 seperate ones, one on the front for your PCV valve and a tapped fitting on the back for your power brakes. You may need to tee the PCV and power brakes together if you have power brakes. The throttle connections should be close, the 3310 is dual feed so the fuel line will be on the front. All the rest should be ok though. If you like Edelbrocks I would try a 750, if you feel more comfortable with them.

Dave

On a Holley, they just have one big Vacuum fitting for PCV/Power brakes, its on the back. Your Edelbrock has 2 seperate ones, one on the front for your PCV valve and a tapped fitting on the back for your power brakes. You may need to tee the PCV and power brakes together if you have power brakes. The throttle connections should be close, the 3310 is dual feed so the fuel line will be on the front. All the rest should be ok though. If you like Edelbrocks I would try a 750, if you feel more comfortable with them.

Dave

Thanks, Dave. I actually have the PCV fed off the rear and the power booster fed off the manifold via a tap behind the carb. Up front are the vacuum advance and the vac. modulator (TH350). I will ask around to see if anyone has a 1407 which will be more of a "direct swap", and if not will try and goose him to get that 3310 sent over my way. I really feel like I need to know one way or the other. If the peroformance I believe I'm lacking is due to this deficiency I'd like to get it taken care of sooner than later!

I build alot of carbs, the 1405-1406's work ok, on fairly stock small blocks. You are running 4.10's and a healthy sounding small block, the 750 should work ok.

Dave

I build alot of carbs, the 1405-1406's work ok, on fairly stock small blocks. You are running 4.10's and a healthy sounding small block, the 750 should work ok.

Dave

Thanks again. I think that's the road I'm going to explore. Especially since I looked at my 1405 last night and saw that someone hacked off the tab where the return spring needs to hook up. WTF???

p.s.--I'm running what was on the car when I got it...a '92 Holley Dominator dual plane alum. intake. Should it be OK with a 1407 in your opinion?

Dual plane, yes.

Dave

Sounds like your engine is somewhat similar to mine. I have run four different carbs at the drags, and the #4779 750 double pumper gives best ET and speed. I run the times in my signature with 4.11 gears, shifting at 5700 and crossing the stripe at 6000. The others I ran were a #3310 750 vacuum secondary, a #4777 650 double pumper, and a 650 vacuum secondary (can't recall the list number).

Also, to back up what Chris stated above, a #3310 will work on just about anything. I have a totally stock 350 in my truck, and I put the #3310 on it because I already paid for it and had it handy. It works mint.

Sounds like your engine is somewhat similar to mine. I have run four different carbs at the drags, and the #4779 750 double pumper gives best ET and speed. I run the times in my signature with 4.11 gears, shifting at 5700 and crossing the stripe at 6000. The others I ran were a #3310 750 vacuum secondary, a #4777 650 double pumper, and a 650 vacuum secondary (can't recall the list number).

Also, to back up what Chris stated above, a #3310 will work on just about anything. I have a totally stock 350 in my truck, and I put the #3310 on it because I already paid for it and had it handy. It works mint.

Thanks, Mike. Yup, I'd imagine it's pretty close to your setup. How does yours behave on the street with a 750 double pumper? Also, what type of fuel pump/fuel line diameter are you running? One more question...choke? Do you use any choke on yours and if so what type? I rarely drive my car in the winter so I have none hooked up right now.

I use a Carter 172 pump and a -8 line from pump to carb, although I would bet a stock pump and lines would work fine on a 13-sec car. I also added the Holley electric choke to my carb. The street manners are great. My car doesn't have a very big cam, nor a loose converter, nor extremely high compression. It idles very smoothly, doesn't foul plugs, and works just fine on the street. FWIW, I don't think the 4.11's made the car appreciably quicker than the 3.42's I used previously.

I use a Carter 172 pump and a -8 line from pump to carb, although I would bet a stock pump and lines would work fine on a 13-sec car. I also added the Holley electric choke to my carb. The street manners are great. My car doesn't have a very big cam, nor a loose converter, nor extremely high compression. It idles very smoothly, doesn't foul plugs, and works just fine on the street. FWIW, I don't think the 4.11's made the car appreciably quicker than the 3.42's I used previously.

Good info, Mike. Thanks! :thumbsup:
Mine's 10:1 and runs 93 octane min. My stall speed is 3000 rpm and the lift on the cam (I was told) is .530
I think I'm gonna start watching Craigs List and e-bay for a good donor.

I'm running a 1407, It seems to work good other than a few issues, I'm going to get a QFT/ ProForm here soon though.

I switched from a edelbrock 650 to 750 on my vortec 355 with voodoo 60103 cam (.504 lift). It made a noticable difference in power, might have been because the 650 wasnt tuned rich enough, but im very happy with the edelbrock 750

what criteria would you need to fulfill in order to support 750 cfm on a 355?
The main two factors are CID and Max RPM.
Secondary factors include expected volumetric efficiency; and the style of intake manifold used.

RPM X CID / 3456 X VE X Manifold Correction Factor = Baseline carb CFM needed.

So, for a 355 with a performance-oriented dual-plane manifold and healthy cam:

6750 X 355 = 2,396,250

2,396,250 / 3456 = 693 (where 3456 is a constant that takes into account the number of cubic inches in a cubic foot; and the fact that your engine is a 4-stoke.)

693 X .85 = 589 (where .85 is a wag at your VE)

589 X 1.3 = 766 (where 1.3 is a wag at your intake manifold's efficiency.)

You'll have to turn that 355 somewhere above 6,500 to get the full use of a 750 carb. If you turn it to 7K, you'll maybe need a bigger carb.

As I said--this gets you "in the ballpark" for carb size.



I have been told by a couple of friends the 1406 isn't enough for my motor, even when I changed the rods and jets near the max. it can accept.
Changing rods 'n' jets doesn't really affect the CFM.

Something a lot of people don't know, or have forgotten, the 302 Z/28 engines ALL came stock with a 780 Holley. Screamers!
(it was rated 780, although, I think they were more like 750)
I'm thinking the original GM carbs had downleg boosters, while the aftermarket (3310-x) carbs have more restrictive straight boosters. If true, that might account for the 30 cfm difference.

You may need to tee the PCV and power brakes together if you have power brakes.
But tee-ing a PCV into the booster hose will KILL vacuum to the booster. Bad idea. Better to fabricate another PCV vacuum port on the front of the carb between the primaries so the PCV fumes are nicely mixed with the incoming fuel/air mix; and distributed to all eight cylinders as evenly as practical. (Drilling a carb spacer should work OK if the carb throttle body doesn't have a suitable port.)

The main two factors are CID and Max RPM.
Secondary factors include expected volumetric efficiency; and the style of intake manifold used.

RPM X CID / 3456 X VE X Manifold Correction Factor = Baseline carb CFM needed.

So, for a 355 with a performance-oriented dual-plane manifold and healthy cam:

6750 X 355 = 2,396,250

2,396,250 / 3456 = 693 (where 3456 is a constant that takes into account the number of cubic inches in a cubic foot; and the fact that your engine is a 4-stoke.)

693 X .85 = 589 (where .85 is a wag at your VE)

589 X 1.3 = 766 (where 1.3 is a wag at your intake manifold's efficiency.)

You'll have to turn that 355 somewhere above 6,500 to get the full use of a 750 carb. If you turn it to 7K, you'll maybe need a bigger carb.

As I said--this gets you "in the ballpark" for carb size.



Dude...you're awesome! Excellent analysis! Of course, I'm a mechanical engineer and I'm trying hard not to call you a nerd (with all due respect, of course!)

Seriously, though, my motor rarely sees 5K cruising around town and back and forth 7 miles to work. Knowing that do you think I ought to dial in the Eddy 1405 and call it a day?

Tom, great questions, good topic. I'm running a 625 CFM on a 355 and am considering going up in carb. This is great information that will help me make a decision also.

Dude...you're awesome! Excellent analysis! Of course, I'm a mechanical engineer and I'm trying hard not to call you a nerd (with all due respect, of course!)
Yeah, but I can't spell "4-stroke".

Seriously, though, my motor rarely sees 5K cruising around town and back and forth 7 miles to work. Knowing that do you think I ought to dial in the Eddy 1405 and call it a day?
If it was me, I'd be looking for a Q-jet to rebuild and tune.

But since you've already got the Edelbrock--yeah, jet it as needed and drive it.

By the way, that CFM formula I used came from the Edelbrock web site...

Yeah, but I can't spell "4-stroke".


If it was me, I'd be looking for a Q-jet to rebuild and tune.

But since you've already got the Edelbrock--yeah, jet it as needed and drive it.

By the way, that CFM formula I used came from the Edelbrock web site...

I think that's what I'll do and then take it from there. In pursuing a better-tuned car the only thing I haven't touchd is the distributor. It's an older HEI piece and I suspect some wear and a barely-functioning vac advance. I think I'll save $ on a carb right now, use the 1405, and look at putting time into the dist.

p.s.--Calling Schurkey a nerd last night was my 500th post!! :hurray: