408 carb question

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jcmmurray

jcmmurray

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I have a 408 with stock J heads, un ported and mild cam. Currently have a 600 ede carb and it works fine for now. To tell you the truth I haven't tuned anything quite yet until I'm done with the car so im not entirely sure how it will act after tuning. Wiring harness and full MSD ignition is now installed. My question is how much will I benefit by putting a bigger carb on and what would be good for the set up I have . I can't see putting anything over a 650 cfm with an electric fuel pump will help at all with the heads I currently have bolted on but maybe I'm totally wrong and should throw a 750 dp on and gain all kinds.?? I'm am no pro but I always kinda giggled at fellas putting huge carbs on with out bolting on the stuff to handle it. Any input?
 
I am building a 408 right now. It will have lightly worked Edelbrock heads and a Comp Xtreme Energy roller cam. We plan on running a gasket matched Air gap intake and a 850 Holley carb. I have an Edelbrock 600 cfm on my 340 now, and it will be for sale shortly

I'm no expert but I have been reading about these strokers for almost a decade now. I would think that you would see some benefit from running a 750 cfm carb. They can be picked up for cheap and would be worth a try.

.
 
750 for sure.. Im running a 750 holley vaccum secondaries on my 340 with stock j heads and a mopar purple shaft cam .484 and it loves it.
 
i have a used prob needs a rebuild dp/df 750 holley vac secondaries for sale i need cash to finish my motor bad 125.00 + ride take it now i will find a new 1 when i get my motor done i have a mech i can use for now pm for # and pics or leave a addy to send pics too
 
I'd put a double pumper 750 on that 408 at a minimum.

BTW a vacuum secondary carb isn't a double pump, it can be a dual feed.
 
crackedback said:
I'd put a double pumper 750 on that 408 at a minimum.

BTW a vacuum secondary carb isn't a double pump, it can be a dual feed.
Click to expand...

I'm looking for an 850 DP, and trying to decide whether I really need the choke or not. No "cold" weather driving, but would cool starts be a problem without the choke?
 
To be honest with ya, a lot will depend on the cam specs and gear ratio/tire size.
Considering that Ma MoPar themseveles put a 600 AFB on top of a 440 in the Chrysler Imperial in '66 and other years.

They had hwy. gears and low stall and etc... That make a 600cfm carb a good choice.
You lack info at this point.
Your stock J head flow about 200cfm. So in a way, there's not much call for more CFM if you have a small cam and hwy-ish gears and such.
 
I wish I knew exactly what cam is in it. When I say mild I kinda mean fairly stealthy. Idles hard / drops hard . I should get ahold of the guy that had it built. (Lost contact) , what I should do is just get a 750 and see what happens. Can always sell one of them or keep it like the rest of the junk I have. I probably would buy that carb off you Winstoninwisc but by the time I pay for customs and shipping to Canada I will have a brand new one.
 
I've had a 408 since 2005 in a 3500 pound car,Hughes 3742AL cam,Eddy heads,2500 stall and 3.55 gears.Down the track about 6 times,so street driven.I had a 750(3310) on it,tryed a 82751 750 HP street carb,then a 4781 850 because everybody said I "needed more carb".I wasn't satified with anyone of them.Got a 4776 600 from a friend,ended up downing the front jets one # to get rid of the stink,but upped the back jets three #'s.Love it,better throttle responce,better gas mileage and a more injoyable ride.So remember everyone will tell you what's "best for you" and most will say I'm full of it but it's all up to your combination and how you drive.My opinion,don't drown it.
Also my plugs look perfect,zero issues since assembly and it consistly see 6500rpm.So with your stock heads and "mild cam" try your carb,read your plugs and let them tell ya.Just my thoughts.
 
If a 408 likes a 600 better than a 750-950 especially with that cam, you need a better tune up. JMO
 
What's the timing profile on your engine, initial and total? Because it's got the classic symptoms of an engine that has an inadequate timing profile.

I've got 340-360 with bigger cams than that hughes stick with 800-950's on them and you can stand behind them and not get gassed out. It's got nothing to do with the size of the carb!
 
I'm just waiting on JCM's cam specs and his gear ratio and tire size to really make a suggestion. The 408 in a stout configuration can use all the CFM you can give it.
In a Incomplete description looking for help, there is to much missing info to correctly make a call. The stock heads and a "mild" cam description leaves to much to assume.
 
I believe the question was about a carb on a 408 with unported J heads and mild cam(that no one know the specs of) so I gave my opinion and hoped he wouldn't do the classic over carb.
 
A 408 with stock J heads and a stock 340 cam should chew up every bit of a 750 pretty easily and make a bunch of tq to pull any gear/converter combination. It'll die off at 4500, but be a stump pulling SOB up to that point

And like anything else, if the timing set up is off, anything will run like junk, especially at idle.
 
68sedan said:
I've had a 408 since 2005 in a 3500 pound car,Hughes 3742AL cam,Eddy heads,2500 stall and 3.55 gears.Down the track about 6 times,so street driven.I had a 750(3310) on it,tryed a 82751 750 HP street carb,then a 4781 850 because everybody said I "needed more carb".I wasn't satified with anyone of them.Got a 4776 600 from a friend,ended up downing the front jets one # to get rid of the stink,but upped the back jets three #'s.Love it,better throttle responce,better gas mileage and a more injoyable ride.So remember everyone will tell you what's "best for you" and most will say I'm full of it but it's all up to your combination and how you drive.My opinion,don't drown it.
Also my plugs look perfect,zero issues since assembly and it consistly see 6500rpm.So with your stock heads and "mild cam" try your carb,read your plugs and let them tell ya.Just my thoughts.
Click to expand...

Would that cam in a 4" stroke small block make power up/near to 6500 rpm? Seems like it would drop off around 5800-5900 rpm: http://www.hughesengines.com/TechArticles/10408416strokerdynotestingsept2002.php
 
Alright put 850 on it,set your initial to 30 total to 36 and don't use your vaccum advance, put a 3500 stall in it and have fun haulin' your fuel truck around.Classic 60's thinking........I'm out.
 
Longer stroke engines make power earlier and drop off faster when compared to equal sized CID engines. Increasing the size of the displacement makes more torque and HP everywhere.

If you had 2 engine displacing 370 cubes, one a big bore short stroke engine like a 340 just bored out to the 370 CID mark and the other is a 360 with a stroker crank like what MoPar used to sell making 370 cubes with the standard 4 inch bore, you would find the pattern I spoke about above.

MoPar used to sell a verity of stroker cranks for the racers to fit and size a engine to the track and or class they raced in. Short tracks and road race (read; lots of twists and turns) would like a longer stroke crank for early torque to come off the corners easier.
Long straight away tracks would prefer a short stroke crank for higher speeds down the straight aways. Normally the turns at high speed tracks are not so tight as to loose a lot of speed. So torque was not of a major concern on the long turns as much as the short tighter turns of smaller tracks and road courses.

Getting power to rise and continue to and beyond 6500 in a 4 inch are requires more cam.
(As a basic starting point. The rest of the build should reflect that as well.)
 
So use your vacuum advance in your truck/street bound ride.
On your race ride............
 
I run an 850 dp on my mostly stock 360 and don't think it's too big at all. After tuning it starts, runs, and drives just as good as the 650 that was on it before. The only difference is it goes faster. Heck I even get 20+ mpg.
 
20mpg. Wow. I dont get that in the gf's civic. I didn't intend on opening up the big carb small carb argument. In a way I'm on both sides of the story here. But still believe there is such a thing as over carb. I'm gonna have to pull the valve cover and roll the crank to a dial to see what I have for a cam as I'm now embarrassed to say "mild" . Lol I'm just gonna plug and play with the 600 and see if I can get a hold of a big carb to see the difference. I appreciate everyone's input. 68sedan. Where are you at in N.S.
 
Ill be home to check my cam in about a month but I can tell you I have 235/60/14 tire with 3:23 and a 4 speed. Will be changing to 275/50/15 Hoosier Q/T and 3:91 gears , keep the 3:23 in the other housing for street. Looking to get somewhere in the mid to late 12 sec .
 
360, xe268H, j heads, LD340, dougs headers, MSD distributor made 350hp and 400tq with a ootb 4779 750dp, no jet changes. It was very close OOTB.

With 904, 2500 hughes converter, 3.00 gears and 245/60/14 tires, it got 20mpg going 65 on the highway to and from spring fling. It also ran right at 105 MPH in the 1/4 with the same jetting which was fat for the altitude. The car wasn't on the mat until after the 60' mark so I'm guessing there was a bit more MPH in it.

Pick carb and learn to tune it, which includes getting the timing set properly. Can't tell you how many fuel belching stinky cars I've fixed over the years that come in with decent sized cams and 10* or less of initial timing. I don't even set stock 318's at 10* initial. More camshaft = more initial timing. Take that for what it's worth.

I stick with my suggestion, a 750DP or a proform main bodied 750dp. Ask UOP how much of a difference the proform body I loaned him made on his car.
 
That's good advice crackedback. I was in the middle of setting my timing when I blew my MSD box. Long story. Anyway I'm gonna play with it myself so I learn . Be the only way to do it and know what is right and wrong. Thanks and I'm here to listen to all opinions for my knowledge, someday hopefully I can pass it on.
 
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