I have a 600cfm Holley DP that I am planning on putting on my 300. The block is 60 over. Stock crank. Heads are milled 30thou. Offenhauser 4b dual plane intake. And am in prosess of doing port n polish job with heads and intake. I plan on putting small turbo ( or 2)on in future (soon as I can afford all the exhaust mods I have to make).. Would the 600 give me problems On the engine with current mods? I Would leave truck down while I finish up everything but wife getting bit pivish at me . So was hoping to put carb on with stock exahust and drive for a bit.

 

I think that the 600 is WAY too much carb...390 CFM is about the MAX. they can stand...

 

I say the 600 is too big. The 500 is about as big as you could go on a near-stock 300.... Every time someone brings this up, they say how their 600cfm runs just perfectly, but never post what their setup is for others to base their tune off of. Odd.


-=Whittey=-

 

I agree with the other guys. A 600 flows enough air to feed 400 HP. There are very few 300's that wind tight enough to produce 400 hp naturally aspirated. If you do the turbo later it might be OK, but I would still go with a vacuum secondary carb. Double pumpers are a waste unless you are building a race only vehicle. Check out the new Demon Jr. 525. I tried a Demon a year or two ago and can say that I'll never buy another Holley. The Demon is so much nicer in every aspect it's unbelievable, and they are still under $300.

 

.... Every time someone brings
>this up, they say how their 600cfm runs just perfectly, but
>never post what their setup is for others to base their tune
>off of. Odd.
>
>
>-=Whittey=-

Cylinders bored .030 over, head milled .010, ported (be sure to grind off those air injection bosses), polished, valves unshrouded, but stock, Comp RV cam, Holley 600 with 1.5" four hole spacer, Heated Offy DP, MSD coil,Champion platinum plugs, stock wires. TFI ignition(works well if you rig up the TPS fromthe stock carb), Clifford headers, high-flow cat, Summit turbo muffler and 2 1/2" pipe out the side.
Carb set-up;
50cc accel pump with big dark maroon cam. The white cam works too. Big squirter out of a double pumper(don't recall just what #), hollow screw. Black secondary spring, #68 main jets in the summer, 72's in the winter. Manual choke.The idle mix is a 1/4 turn rich, helps eliminate off idle stumble.

Specific enough for ya, Whittey?

No, it ain't stock, but it runs, as you say, just perfectly. Don't know that it would work as well without the headers or big exhaust, but hell, if you've got one on the shelf, give it a shot.

 

Oh, forgot. 6.5 power valve with blowout protector. Higher # will give you better mid range, but I was going foreconomy. BTW, around 18 highway, 13 city. Not great, but better than some.

 

Well my experiance tells me that most ford guys kinda wish they were chevy guys for this reason. A chevy engine (for some unknown reason) will handle too much fuel (need and example, my luv has a 120cui whith a 380cfm carb) and run just fine, whereas a Ford engine will run well but as soon as the secondaries open you will start bogging the engine whith isnt good, my sugestion would be go whith a 500-550cfm carb that should work realy well. My 300 will be running a 750cfm spread bore becouse i have one off a v-8 only untill i can get a smaller carb, if you have to run a large carb make shure you can disconect the secondaries and you should be ok whith a 600cfm.

 

Horseman: Thank you. I know i've asked at least a half dozen people what they were running, but they never replied. Sounds like you've got a heck of a motor there. Ever have it on a dyno?


-=Whittey=-

 

No, never dyno'd it. Thought about it, but don't know where to find one around where I live.
Forgot to tell you the cam profile. 212 @ .050, 110' separation.

The best thing about the 600 is it's vacuum secondaries. They won't open until the motor can use the fuel. Rarely, if ever, will it bog when they open.

 

>50cc accel pump with big dark maroon cam. The white cam
>works too. Big squirter out of a double pumper(don't recall
>just what #), hollow screw. Black secondary spring, #68 main
>jets in the summer, 72's in the winter. Manual choke.The
>idle mix is a 1/4 turn rich, helps eliminate off idle
>stumble.

That doesn't sound like it runs perfectly to me. You have to change the jets on a seasonal basis, you have a giant accelerator pump shot to cover a bog, and that still didn't do it so you have to run the idle mixture too rich to cover it up. All symptoms of too much carb. You could probably get rid of the stumble and have the idle mix set properly if you opened the secondaries slightly. This would allow the primaries to be closed slightly and cover up more of the transfer slot. Many off idle stumbles are because the carb tries to transition to main metering too soon. Having more of the transfer slot above the throttle blade at idle allows the engine to use the idle circuits a little longer.

 

Hey Horseman,
A little off topic but how does that summit turbo sound? I want to get rid of my tinny sounding one chamber flowasters. Do you have any souns clips of it? Thanks

 

[updated:LAST EDITED ON 09-Jan-03 AT 10:37 AM (EST)]You could probably
>get rid of the stumble and have the idle mix set properly if
>you opened the secondaries slightly. This would allow the
>primaries to be closed slightly and cover up more of the
>transfer slot. Many off idle stumbles are because the carb
>tries to transition to main metering too soon. Having more
>of the transfer slot above the throttle blade at idle allows
>the engine to use the idle circuits a little longer.

I think a lot of the off-idle stumbles these motors experience has to do with the long runner intake. That said, my idle is set at 800 rpm, the idle screw just touching the seat and the primary butterflys nearly all the way closed. I would think that having the primaries cracked would just have the effect of further leaning the mixture, but it's an interesting thought. Yes, it's a big pump shot, but there's no black smoke on acceleration, so it's not too big. And changing jets on a Holley isn't too unusual around here. Heck, the boys at the track change 'em almost hourly, depending on pressure altitude. That's the thing about Holley's, they are almost too sensitive to atmospheric conditions.

I just went over to www.bgfuel.com/demoncarbs/ They recommend a 625 cfm for engines 302 to 400ci (with the bore, mines about a 302) and my cam profile 210>..<220 @ 50 . So basically, they are recommending a bigger carb! Looks like a nice product, though.

 

>Hey Horseman,
>A little off topic but how does that summit turbo sound? I
>want to get rid of my tinny sounding one chamber flowasters.
>Do you have any souns clips of it? Thanks

Sorry, no .wav. But I think it sounds pretty good, nice low rumble. Not like a V8, but you can definitely tell its no box-stock six. And for $20,Profanity Removed, right?

 

Changing jets on a track engine is not unusual, but they breath much better and put much more emphasis on the carburetor. Those guys are also looking for power gains on the order of 1/2% or maybe even less. On a street engine you shouldn't have to change the jets on a seasonal basis. I have one customer with a 73 Vette that is set up strictly for road racing. The engine is basically a 350 built to 1970 LT-1 specs. I put a Demon 750 on it, which is really a little much for his engine, and set the carb up at the beginning of last season. He raced it in weather ranging from 30 degrees to 105 and never cracked it open.

BG recommends the 625 for engines from 302-400 cubes because until very recently it was the smallest carb they made. They would rather recommend their own carb that's too large than the proper one from a competitor. They are also basing their recommendation on a V-8, which for any given displacement spins roughly 25% faster than a 6. A 302 that makes 300 ft-lbs of torque will have to spin faster to make the torque because of the shorter stroke. However, since it is the same displacement but spinning faster it needs more air. I would be shocked if you called BG for a recommendation and they recommended anything but their new 525 Demon Jr. 390 cfm is enough air to feed 260 hp, how many 300's are out there that really make much more than that? On 99% of the 300's out there I doubt there is 5 hp difference between the 390 and 600 if they are both tuned to run optimally.

Another reason most people probably run the 600 is because the 390 costs considerably more than the 600.