Again - is it worth it? Holley 600VS to 750VS

[MikeyM]

Hi all,

I've searched and read all kinds of semi-older threads on the pros and cons of this and was hoping for some fresh opinions and input. Currently have a '69 N96 all stock 383HP / 727 / 3.23s, 64k original miles with the exception of an MP electronic ignition, Flowmaster 40s and a Holley 600VS (80457-2) that I've managed to dial in pretty good with jetting, squirter, etc. It all came with the car. Also pretty sure I have a replacement torque converter cuz there's no drain plug. No idea if it's stall or not, haven't driven one, don't know how to tell, but it feels stockish, I guess. To me, the low end feels pretty strong. In the next few months the plan is to install Doug's 1.75 headers and 2.5" exhaust as the foundation for future mods as time and funds allow (cam, maybe good aluminum heads but way down the line). Since it's an N96 car, I'd also go with either a DP4B or Action plus and loose my existing 1/2" 4 hole spacer so the intake would fit.

The engine really never sees over 5k but I've taken it to 5300 on occasion and wonder if it has more to give. According to the calculators I probably wont "need" a 750 but would it give a worthwhile increase in power from mid-top end? How about throttle response? The current 600 is great on throttle response. I tried an Eddy 750 that was "meh..". I changed metering rods on it but I didn't put near the time into that as I did with the Holley. I drive on the freeway quite a bit at about 75 and am curious to see what the difference in acceleration would be from, say, 3300 on up.

As some of you may know, I've been out of the hot rodding game for decades so I appreciate your input.

Thanks,
Mikey

 

[RemCharger]

The best way would be to go on a Friday night at the track and see what you currently have. It's the only real gauge other than a dyno.
But a 650 DP will almost always perk up a stock 383.

 

[Cranky]

I've had and still do have several carbs to experiment with but will tell this one story about a 10 second car that ended up with two 750 tunnel ram carbs on it and it just kept on going faster. Had many tell me it was over carbed. Oh well. Did the same thing with many street cars and they too went faster with bigger carbs. Thing is, if you want anything that gets good gas mileage, go small. Also, the combination needs to be right....

 

[BLK 68 R/T]

I had a bone stock 70 Superbee, 383 4 speed car, 3.23 gears. One weekend I had the opportunity to install an 850 speed demon carb. Was like driving a race car after that. The improvement over the stock ~600 Holley was amazing. The next weekend I put in a 4.10 gear that I got to borrow for a few weeks. That Superbee was virtually untouchable.

 

[RJ Squirrel]

Really just boils down to how you plan to drive it, I have a 600 carb on my 440, runs great, real happy with it. We mostly just cruise around on 2 lane country roads me and Lenny my dog.

 

[MikeyM]

Thanks for the replies. For the money spent on headers and having a shop adapt them to my OEM exhaust (temporarily, until I can get the 2.5" pipes installed), would those funds be better spent on the carb / intake combo, running the current 600 (temporarily, of course) with the DP4B into the OEM HP exhaust manifolds and do the headers later? Or would the engine be somewhat choked with the HP manifolds? I realize some 383s came with 750s (right??) and the OEM intake / exhaust manifolds and ran very well but headers seem to be the logical 1st step in trying to apply the limited funds to get the most bang for the buck. For what it's worth, my intake is the OEM '69 unit 2806301, which I read seemed to be the best performing of the OEM bunch.

Thanks again,
Mikey

 

[Bee1971]

Most street cars

Operate on the idle/cruise circuit 80% of the time

NO 1968-1971 383 HP left the factory with a 750 CFM Carburetor - None

With that said
If you where to take a factory 1968-1971 383 HP and replace say a factory Carter AVS 630 CFM Carburetor with a factory Carter AVS 750 CFM you would definitely notice a difference in performance on acceleration full throttle

With the modifications you might bee considering, unless you plan on the idle/cruise circuit 100% of the time , a Holley 600 CFM would bee a waste of time at any performance level

My opinion of course

 

[MikeyM]

Thanks, Bee. would the OEM HP manifolds flow enough for a 750 with a DPB4 / Action Plus? Again, the engine will likely never see over 5500 and even that would be pretty rare. If so, it sounds like that might be the best way to go instead of headers - at this time.

Thanks, Mikey

 

[496 polara]

It all depends on what you want.

The dp4b is a good upgrade IMO.

The 2.5 mandrel exhaust is a great upgrade and will support all your future upgrades.

Headers is up to ya.Yes there is power there but some folks like the simplicity of manifolds and you already have them.

If you are happy with the carb you have keep it. If you want a little more a 650 would help but I would stay with the vacuum secondary.

A 750 vacuum secondary will work fine and make more HP up top but may lose a little responsiveness down low with the larger throttle bores. I would be in the camp if you do headers then I may consider the 750 but probably not until headers were installed.

 

[Budnicks]

Get a Holley Street Avenger 770cfm VS carb/dual inlet & bolt it on
or if you can find a good 3310 Holley 780 VS
or the old 750 cfm 3310 VS carb, then go with it...
both carbs have the same size throttle plates & venturis
(*85% of 770cfm is 654cfm)

the 600cfm Holley won't hurt ya' a ton but at WOT
(wide open throttle for extended periods, like drag racing or just showing off)
but you won't get the best performance or drivability out of it

CID X RPM div. by 3456 = total CFM (at near 100% efficiency)
*you need about 85% of that # min.

example
383cid x 5,800rpm div. by 3456 = 642cfm (*85% of 770cfm is 654cfm)
(5,800 rpm is about when the car will start to nose over, with stock valve springs & cam)

1-7/8" Headers (long tube headers espec.) will add about 10% more power across the board
Torque & HP properly tuned, over the stock HP manifolds
1-3/4" long tube or a good quality 'mid length headers', like the Hedmans offer
will add like 6%-7% increase across the board Torque & HP,
over the stock HPs too

more camshaft & carb, cylinder head etc. more flow is needed

depends on what you're doing with it

a 2-1/4" exhaust like the OE RRs or Charger R/Ts Had,
is plenty for a just cruising & a lil' fun

But you can get another maybe 5% out of it with a mandrel bent 2-1/2" tube & H-pipe
good flowing mufflers, you can see thru
or even a 3" & an X-pipe or H-pipe, for more 'all out' performance stuff

what goes in, must be able to be let/exhausted out
depend on what performance you want,
you don't have to have it floored for any of the combos
to get better performance with more air flow,
bigger carb & better intake & nonrestrictive exhaust system
(Edelbrock Performer RPM & a properly tuned Holley, is hands down
best Street/strip combo, you can get for the $$$)

Street Avenger 770cfm VC dual inlet Holley below

 

[BSB67]

Unless you are going to go to the track and do back to back testing, you’ll never really know what the improvement is. It is unlikely you’ll be able to tell the difference on the street.

 

[MikeyM]

Man, great info all. Thank you so much.

Budnicks, that info is exactly what I was hoping for, thank you. While I know the numbers are rough, it gives a general idea of what to expect on a 383, give or take. Another important piece of this story is that since it's an N96 car, I really want to keep it like that. I do believe it helps a little based on cooler temps, etc. so I did happen to find a DP4B intake and pulled the trigger on it. I would love to use the perf RPM for obvious reasons but I'm really hoping for the most low end I can get (3.23s) while still retaining the mid-top end advantages of the 383 and, from my research and understanding, the DP4B is the best compromise.

The car is definitely a driver and I drive it on the highway quite a bit (NorCal). Freeway speeds are typically 75-80 and I'm usually around 75 with the occasional blast to pass. Also, for those short onramps, it's nice to have the power I have - I know most of you have driven larger engines but this is my first BB so, again, it's nice to have getting on the freeway. The ultimate goal is to have the most low end while still retaining good mid-top range, all the while getting the most power and efficiency from the engine.... given the performance components. Building it part by part, 1 phase at a time, certainly isn't ideal but it's kinda how I have to go at the moment so doing the right things in the order of cost vs. gain / bang for buck would be nice. For example, maybe start out with the DP4B, run that with the 600 for a bit, then go to the 750, then headers, then the cam. Something like that. The BIG mods won't be for quite a while.

Again, thanks for all the input, this is a huge help.

Mikey