Tired 307 bogs badly under acceleration...

[Strictly Attitude]

Actually you have that quadrajet awsome carb Brian posted about one recently use that would be a good way to go for now but don't get caught in the now because waiting for later pays more dividents.

 

[grumpyvette]

Strictly Attitude has a valid point, that concentrating on buying components compatible with the intended 383 sbc engine , rather than wasting effort on patching up the 307 sbc currently in the car, that is a compromise,and installing the new intake and carb,(of either size) in the mean time ,will be much more cost effective.
now having done this type of upgrade several dozen times over the years I doubt there will be a huge advantage in use of the 750 cfm carb, but yes your almost certainly going to gain a few peak horsepower with the larger carb on that 383 over what youll see with the 625cfm version and its not going to cost that much more cash or choosing the larger or smaller carb ,is unlikely too have much real, if any effect on the 307 simply because its a vacuum actuated secondary venturi carb that opens as flow demands warrant , youll only see full flow at peak rpms and you can very easily tune the carb so it provides what ever tip in rate or flow rate increase you find to work best.
keep in mind your never going to reach a true 90% efficiency level, even at peak rpms and youll more than likely spend 97% or more of the engines life spinning well below peak rpms, or in reality make decent power past about 6300rpm with the engine combo , with that cam or anything even similar in klift or duration, in your proposed engine building and with those limitations in mind we can calculate the likely carb flow

http://users.erols.com/srweiss/calccarb.htm

http://www.summitracing.com/parts/wnd-8501/overview/

http://www.summitracing.com/parts/dem-1901/overview/

http://www.summitracing.com/parts/dem-1904/overview/

 

[JimmyDuncan]

Ever thought about cleaning up the dizzy springs are cheap and elbow grease is free. Yes the carb you want for the 383 and the one for the 307 arenot gonna be the same. Used edelbrocks are usually cheap not sure about in your neck of the woods. But concentrate on the 383 if that is your goal. A little sacrifice now will pay off later. Focus lay out a budget and a plan and stick to it!!!! Other wise you are settling on that 307 car parts add up quick money is tight it's proper planning that makes projects happen. I would try not to purchase anything that cannot be used for your other engine build. Fuel system stuff ok the carb is a tough one but me I would buy the carb for the 383.

Yeah, thanks for the advice. I agree, I really don't want to spend any $$ on the 307... If I can buy parts that will fit the 383 build perfectly and will work on the tired 307, then I will go ahead. More so if they will make the car run better in the mean time... If you think the points dizzy is worth putting some free elbow grease and cheap springs into it, then maybe I'll give that a crack... Guess it can't (probably) make it worse

Out of interest what sort of dizzy would you recommend to buy in the future? The MSD pro billet models look great, but are very $$... Are there good value options out there?

 

[JimmyDuncan]

Actually you have that quadrajet awsome carb Brian posted about one recently use that would be a good way to go for now but don't get caught in the now because waiting for later pays more dividents.

The quadrajet would require an adapter to run on the Performer RPM intake yes? Which I guess would be a relatively inexpensive, option to try... I don't know if it will need a rebuild kit or not though... If I can pick up a used adapter for next to nothing, it would be a fun exercise if nothing else

 

[JimmyDuncan]

Strictly Attitude has a valid point, that concentrating on buying components compatible with the intended 383 sbc engine , rather than wasting effort on patching up the 307 sbc currently in the car, that is a compromise,and installing the new intake and carb,(of either size) in the mean time ,will be much more cost effective.
now having done this type of upgrade several dozen times over the years I doubt there will be a huge advantage in use of the 750 cfm carb, but yes your almost certainly going to gain a few peak horsepower with the larger carb on that 383 over what youll see with the 625cfm version and its not going to cost that much more cash or choosing the larger or smaller carb ,is unlikely too have much real, if any effect on the 307 simply because its a vacuum actuated secondary venturi carb that opens as flow demands warrant , youll only see full flow at peak rpms and you can very easily tune the carb so it provides what ever tip in rate or flow rate increase you find to work best.
keep in mind your never going to reach a true 90% efficiency level, even at peak rpms and youll more than likely spend 97% or more of the engines life spinning well below peak rpms, or in reality make decent power past about 6300rpm with the engine combo , with that cam or anything even similar in klift or duration, in your proposed engine building and with those limitations in mind we can calculate the likely carb flow

http://users.erols.com/srweiss/calccarb.htm

http://www.summitracing.com/parts/wnd-8501/overview/

http://www.summitracing.com/parts/dem-1901/overview/

http://www.summitracing.com/parts/dem-1904/overview/

Ok, thanks Grumpy. Yeah, my main question was whether the best option carb for the 383 would work at all on the 307 in the meantime... If it could add a little better performance to the tired 307 for the winter, while I build the 383, then I'd go ahead and buy it soon. If it was going to be the same or worse on the 307, then I'll leave up on buying it till later... It sounds like you think that the 625cfm or the 750cfm Demon carb would likely be good options for the 383 and would probably work ok on the 307 in the short term..? That way I'm not wasting $$ on the tired 307..

It's interesting that while the 625cfm sounds like the better option, based on the calculations and your advice, but my ego keeps looking at the 750cfm as an option..... Maybe its a guy thing... "Check out the size of my carb!" "oh, you went with the 625cfm..... how cute...."

 

[Grumpy]

go with the 750 cfm if you want too, its a vacuum secondary carb so it automatically matches engine air flow demand

 

[JimmyDuncan]

go with the 750 cfm if you want too, its a vacuum secondary carb so it automatically matches engine air flow demand

You had mentioned that that 625cfm might have better street manners and low end crispness? Particularly in a heavier car?

If a 750 cfm is viable, what do you think of the Holley 3310 carbs? There's a shop nearby that does re-manufactured 750cfm, vac secondaries, electric choke carbs for decent $$.

Every time I look for info on carbs online, there just seems to be a bunch of opinions thrown about, "holley is best!" "edelbrock is best!", "quadrajet is best!"....

 

[Grumpy]

let me go through the way an old geezer looks at this for the benefit of anyone reading through this thread, you certainly don,t need to agree and you can certainly post questions and have everyone on the site tell me where Im wrong, in my reasoning, but after doing similar builds for decades I don,t think I will be too far off.
yes theres an endless list of potential upgrades and yeah we all have limited budgets
Obviously I don,t know the quality of the machine work, the care of assembly or the parts youll use in the final configuration on that 383 sbc build , but we can easily assume a fairly mild cam and an engine designed to maximize power in the 2000 rpm-5000 rpm range as that matches the application were discussing.
the newer street demon is the newest design and its about the simplest to work with, if it was my car Id personally select the 625 cfm street demon but in reality either cfm choice is going to work fine ,and the difference in both power and mileage is going to be rather minor,
http://www.summitracing.com/parts/dem-1901/overview/
ok why your thinking will I select the slightly smaller carb when I clearly stated the larger carb will produce a bit more power, well its really due to being an older guy with a bit of experience and knowing that your going to spend 99% of your time cruising around at under 5000 rpm and gas mileage is going to be slightly better with the smaller carb.
so why would I sacrifice a couple peak hp for what might be only 1/2 or 1 mile per gallon in better fuel efficiency?
its because I fully realize a 3700 lb car is never going to be competitive as a race car ,but the minor increase in mileage is going to over time mater to you.
so why not a quadrajet, thats a no brainer, they have not made those carbs in any numbers nor have they made a great deal of the minor parts for them in years, so simply keeping it up and running might be a problem in a few years.
Why not a Holley?, theres plenty of Holley parts and support, but it takes a bit more tuning skill and most holley 4 barrel carbs are not all that easy to work on,for someone who has not yet gained experience and through that experienced learned about accelerator pumps,power valves jetting,etc. they usually require partial dis-assembly, to make changes and ripped fuel bowl gaskets and striped threads are not all that rare, and your much more likely to have one leak or spill fuel changing jets or making adjustments, now don,t get me wrong they are a quality carb in many models and you certainly can get parts for most of the more common designs.
BTW if you have access upgrading the transmission from the two speed power glide to a properly built 200r4 OD trans will work wonders for both performance and mileage with that 383, Id expect to pick up 4-6 miles per gallon and get brisker acceleration.
Automatic Transmission Gear Ratios

..................1st ...2nd ...3rd ..4th
GM
Powerglide .1.76 .1.00
200r4 ........2.74 .1.57 ...1.00 ...0.67 O.D.

watch the video

now do some calculations
http://www.wallaceracing.com/et-hp-mph.php

suppose just for grins the engine when your done building it produces 320-340 peak rear wheel hp and your car with you in it weights 3900 lbs thats assuming youll get about 400 flywheel hp.
(probable double the current 307 engine current power)
(I think those will be reasonably close guesses) and remember you can change the combo at this point to get a bit more power or mileage but the concepts were discussing should remain fairly consistent and you know youll use an auto trans and your probably not optimizing the converter stall speed or rear gear ratio, or adding slicks, to race the car so if your concentrating on a good street performance combo youll sacrifice some peak power for better street drive-ability and a dozen other factors your unlikely to maximize for max results with the cars race potential, what your doing here is probably coming close to potentially DOUBLING the current 307 engines rear wheel power potential by swapping to a well built 383 but its certainly going to be far more a fun cruiser than a viable race car.
now recalculate with the same weight and maybe...lets be generous here, 6 extra hp from the larger carb (personally I think the difference will be less)
notice the results are not going to do that much for your ability to take on the local racers.
now lets do one other calculation, lets say youll get 12 mpg with the larger carb and 13 mpg with the smaller carb, lets assume, you drive 12,000 miles a year (I know I drive easily double that) thats about an 80 gallon a year difference
(I DON,T KNOW WHAT YOUR FUEL COSTS or how many miles a year you drive, but it should be rather obvious that the potential performance vs cost of operation is skewed a bit here!)

anyone care to comment or discus this a bit?

 

[Strictly Attitude]

I have a billet msd it works fine but requires an msd box also hei is a good cheap option that cam in many cars

 

[87vette81big]

A Q-jet & factory intake would be an easy bolt on the 307.
Taken from a 1978- 85 305 Ci Chevy Caprice Classic in the Junkyard.

 

[JimmyDuncan]

let me go through the way an old geezer looks at this for the benefit of anyone reading through this thread, you certainly don,t need to agree and you can certainly post questions and have everyone on the site tell me where Im wrong, in my reasoning, but after doing similar builds for decades I don,t think I will be too far off.
yes theres an endless list of potential upgrades and yeah we all have limited budgets
Obviously I don,t know the quality of the machine work, the care of assembly or the parts youll use in the final configuration on that 383 sbc build , but we can easily assume a fairly mild cam and an engine designed to maximize power in the 2000 rpm-5000 rpm range as that matches the application were discussing.
the newer street demon is the newest design and its about the simplest to work with, if it was my car Id personally select the 625 cfm street demon but in reality either cfm choice is going to work fine ,and the difference in both power and mileage is going to be rather minor,
http://www.summitracing.com/parts/dem-1901/overview/
ok why your thinking will I select the slightly smaller carb when I clearly stated the larger carb will produce a bit more power, well its really due to being an older guy with a bit of experience and knowing that your going to spend 99% of your time cruising around at under 5000 rpm and gas mileage is going to be slightly better with the smaller carb.
so why would I sacrifice a couple peak hp for what might be only 1/2 or 1 mile per gallon in better fuel efficiency?
its because I fully realize a 3700 lb car is never going to be competitive as a race car ,but the minor increase in mileage is going to over time mater to you.
so why not a quadrajet, thats a no brainer, they have not made those carbs in any numbers nor have they made a great deal of the minor parts for them in years, so simply keeping it up and running might be a problem in a few years.
Why not a Holley?, theres plenty of Holley parts and support, but it takes a bit more tuning skill and most holley 4 barrel carbs are not all that easy to work on,for someone who has not yet gained experience and through that experienced learned about accelerator pumps,power valves jetting,etc. they usually require partial dis-assembly, to make changes and ripped fuel bowl gaskets and striped threads are not all that rare, and your much more likely to have one leak or spill fuel changing jets or making adjustments, now don,t get me wrong they are a quality carb in many models and you certainly can get parts for most of the more common designs.
BTW if you have access upgrading the transmission from the two speed power glide to a properly built 200r4 OD trans will work wonders for both performance and mileage with that 383, Id expect to pick up 4-6 miles per gallon and get brisker acceleration.
Automatic Transmission Gear Ratios

..................1st ...2nd ...3rd ..4th
GM
Powerglide .1.76 .1.00
200r4 ........2.74 .1.57 ...1.00 ...0.67 O.D.

watch the video

now do some calculations
http://www.wallaceracing.com/et-hp-mph.php

suppose just for grins the engine when your done building it produces 320-340 peak rear wheel hp and your car with you in it weights 3900 lbs thats assuming youll get about 400 flywheel hp.
(probable double the current 307 engine current power)
(I think those will be reasonably close guesses) and remember you can change the combo at this point to get a bit more power or mileage but the concepts were discussing should remain fairly consistent and you know youll use an auto trans and your probably not optimizing the converter stall speed or rear gear ratio, or adding slicks, to race the car so if your concentrating on a good street performance combo youll sacrifice some peak power for better street drive-ability and a dozen other factors your unlikely to maximize for max results with the cars race potential, what your doing here is probably coming close to potentially DOUBLING the current 307 engines rear wheel power potential by swapping to a well built 383 but its certainly going to be far more a fun cruiser than a viable race car.
now recalculate with the same weight and maybe...lets be generous here, 6 extra hp from the larger carb (personally I think the difference will be less)
notice the results are not going to do that much for your ability to take on the local racers.
now lets do one other calculation, lets say youll get 12 mpg with the larger carb and 13 mpg with the smaller carb, lets assume, you drive 12,000 miles a year (I know I drive easily double that) thats about an 80 gallon a year difference
(I DON,T KNOW WHAT YOUR FUEL COSTS or how many miles a year you drive, but it should be rather obvious that the potential performance vs cost of operation is skewed a bit here!)

anyone care to comment or discus this a bit?

I really like how you make sense of things Grumpy

Cleared it up for me.

Like you said the price diff between the 625cfm and 750cfm is minimal, but, yeah, I'll probably appreciate the better gas milage on the long cruises to the beach in summer..

And waay down the track when the engine is built and the trans and rear-end are optimised, and I have had fun finding out what the tank will do over a 1/4, then I can pick up a larger carb to rebuild and fiddle with... try for a few extra mph... The videos I've seen of Holley tuning, make me want to pull one apart to play with one day in the future... but, I don't want to be struggling to get the car running nicely in the beginning... I will want to to be as dependable and smooth as possible for the first little while, when I finally get it out on the road..

 

[JimmyDuncan]

I've got a few spare $$, so I'm going to order the Street Demon 625cfm

http://www.summitracing.com/dom/parts/dem-1900/overview/

and probably a Pertronix Street/Strip HEI dizzy (the price is good and the reviews are fairly good... open to other suggestions.. MSD is another couple hundred $$ to me here in Oz) I looked into a pertronix upgrade for the delco, but it would need a rebuild before it I could guarantee it was going to function properly and to buy the parts to do that and the pertronix upgrade would be heading towards the cost of the new dizzy in the end..

http://www.summitracing.com/dom/parts/pnx-d1000/overview/

I have a Performer RPM intake manifold

http://www.summitracing.com/dom/parts/edl-7101/overview/

and a package of chev 350 gaskets which came with the grimy 350 when I bought it (the intake gasket from that should fit the 307 yes?)

I need to order some 12 gauge wire to replace the 18 gauge wire running from the ignition to the dizzy, because apparently I'll catch on fire if I don't.....

Keeping in mind that this is a temporary fit until the 383 is built (after which the carb, dizzy and intake will move to the 383), so I'm trying to only purchase parts that will work in the end game and/or trying to reuse what I can on the 307..

What else do I need to have on hand for the swap over from stock chev 307 intake, 2bbl rochester carb and delco points dizzy?

Any particular sealants or potions that work best?
Any bolts/studs/nuts I must replace rather that re-use?
I'm waiting to hear back form Demon re: hooking up to the stock accelerator linkage and powerglide kick-down..
While I have the intake off, is there any important things that I should check for on/in the engine while I'm in there?

 

[Indycars]

You might want to order an extra gear for the distributor. The 307's camshaft gear maybe
worn and therefore will wear on the new distributor gear. The new gear would go on the
distributor when it goes in the 383 motor. If you have the time, I suppose you could wait
and see, then order if needed.

 

[JimmyDuncan]

You might want to order an extra gear for the distributor. The 307's camshaft gear maybe
worn and therefore will wear on the new distributor gear. The new gear would go on the
distributor when it goes in the 383 motor. If you have the time, I suppose you could wait
and see, then order if needed.

Good idea. I'll keep that in mind.