Take14theroad Posted April 22, 2008 Share Posted April 22, 2008 I am rebuilding a 400 small block (I guess a 406 now) and I need help picking a few final parts for it. The specs are: 10:1 compression ratio Edelbrock Performer RPM Aluminum Cylinder Heads Edelbrock RPM air-gap intake Summit Full Roller Rockers (1.6) Lunati Voodoo Cam- 219/227 at .050 and .468/.489 It is going to be matched up with a TH350, posi rear end, 3.73 gears and dual 2.5 inch exhaust (x-pipe) with headman headers Now that that is all done... I was wondering if I should run a 750 or 650 cfm carb. (I would like to stick with an edelbrock, but i am open to other suggestions.) does anybody have a similar setup? Will i need a 120 GPH Fuel pump? Is it better to use rubber or poly motor and transmission mounts? Thank you very much, Joe Link to comment Share on other sites More sharing options...
kc8oye Posted April 22, 2008 Share Posted April 22, 2008 u would problaby do well to go with a 750. my engine is very close to yours.. (A SMIDGE smaller cam, and stock iron heads) and I run a 600 and it's borderline too small. just make sure it's a vacuum secondary carb.. our cars are just too heavy to make it worth running a mechanical secondary carb. (unless you plan on running crazy stall and high gears) which it doesn't look like you are. you won't need 120gph. I'm using a "stock" replacement mech fuel pump and i have no problems with fuel. and i have it limited to 5psi with an inline regulator. I believe my pump is only 60gph.. might be 80. Link to comment Share on other sites More sharing options...
Take14theroad Posted April 22, 2008 Author Share Posted April 22, 2008 Thank you, The stall speed is 2000. What is the advantage to vacuum secondary on a heavier car? Link to comment Share on other sites More sharing options...
Mike 57 Posted April 22, 2008 Share Posted April 22, 2008 I would go with a 750, the eddy carb will work the air valve in the secondary will work good on the street. I personally prefer a 750 holley with vacuum secondaries. But that is what is great we all have a chance to try what we prefer. Link to comment Share on other sites More sharing options...
Sam (Bones) Posted April 22, 2008 Share Posted April 22, 2008 a vacuum secondary will open gradually as the engine needs, a double pumper opens as soon as you mash it, on a heavy car that doesn't rev as quick, this can cause a bog or stumble Link to comment Share on other sites More sharing options...
Take14theroad Posted April 22, 2008 Author Share Posted April 22, 2008 So the vacuum secondaries will actually help me at low RPM? It's cool that less fuel will make me go faster. I am leaning toward the Edelbrock becuase they are said to be easier to tune and adjust. Is this true? Thank you Link to comment Share on other sites More sharing options...
Cali4nia Monte Posted April 22, 2008 Share Posted April 22, 2008 Yup they are right we have the Holley 4150 750 carb (which has the manual secondaries) and it was a nightmare to get rid of the bog. We still do not have it completely gone but have come very close. We have a 350 crate engine that's got 377+ hp have a TH400 tranny with a 3000 stall and 3.42? posi rear end. In order to get it to run as good as we've got it now we had to take it to a carb guy who completely rebuilt it. In addition we removed a 1 inch spacer (which showed the biggest improvement) and changed the springs in our distributor which was also the carb guys recommendation. Something about it makes the car advance quicker?? We had a Holley 650 before and it had no problems at all....but the car is significantly more powerful with the 750. Anyhow long story short...haha....if we had it to do over we'd probably go with vacuum secondaries next time. ~Jaylene~ Link to comment Share on other sites More sharing options...
Take14theroad Posted April 22, 2008 Author Share Posted April 22, 2008 Thank you very much. It sounds like i am going with a 750 with vacuum secondaries. and a stock style fuel pump. Thank you so much for the help. Link to comment Share on other sites More sharing options...
kc8oye Posted April 23, 2008 Share Posted April 23, 2008 like sam said.. the vacuum secondaries will feed air/fuel only as the engine demands it. with a 'mild' engine and a heavy car with low gears for cruising... the engine doesn't rev very fast, so when you whack the throttle open.. the primaries open up. and that's plenty.. as the revs start to come up and the engine wants more air, it will pull the secondaries open assuming everything is calibrated right. if you run a mechanical secondaries a.k.a 'double pumper' when you whack it to the floor, all 4 barrels open up at once and manifold vacuum jsut dissappears, while there is still no significant velocity to the air in the intake manifold, and the engine cant fill the cylinders effeciently, and you bog & stumble. Link to comment Share on other sites More sharing options...
Heckeng Posted April 23, 2008 Share Posted April 23, 2008 Good description KC. Either carb would be good, anywhere between a 600 to 750. If you assume your engine is 100% efficient, and would rev to around 6000 rpm, it theoretically needs a 700 cfm carb. Your engine will likely be around 80-85% efficient so a 600 would actually be a very good choice, although you could run a 750 and it wouldn't be drastically worse. If you run the larger carb, definitely go vacuum secondary. If you went with a 600 or 650, I'd be tempted to go with a double pumper because the air velocity will be higher in the smaller carb and you'd be less likely to have that stumble that KC was talking about. I'd run those 3.73 gears with either carb and that will help reduce any potential for bogging as well. Edit: Oh yeah, I am voting for the Holley! Link to comment Share on other sites More sharing options...
kc8oye Posted April 23, 2008 Share Posted April 23, 2008 holley says on their website not to use a DP for anything over 3200 lbs. or with low numerical gearing. I would look at a StretAvenger 670cfm vac secondary from holley.. they're about $370 from most places... based on what scott says there. Link to comment Share on other sites More sharing options...
Heckeng Posted April 23, 2008 Share Posted April 23, 2008 That 3200lb limit is just a blanket statement to keep them from making people mad. If they didn't put that up there, everybody would get a Double Pumper for the "coolness factor" of being able to say "it's a double pumper!". They would be put on stock cars, with highway gears etc. That's not what they were intended for. If you have a monte, with 2.73 gears and stock stall, a DP will be HORRIBLE, but if you have some deeper gears, and a little stall, a double pumper will be great. I run a DP and have around a 3k stall, and get no bog. I think Sam is the only one who has ever heard my car, but I don't think he noticed any bog or anything It all depends on your combo. Link to comment Share on other sites More sharing options...
Sam (Bones) Posted April 23, 2008 Share Posted April 23, 2008 I run a pumper too, I have 3.73 gear and a 4000 stall, with that low of a stall...I wouldn't use one Link to comment Share on other sites More sharing options...
Heckeng Posted April 23, 2008 Share Posted April 23, 2008 I didn't see where he stated the stall, I agree with Sam, 2000 is pretty low! I might consider a 2400-2500 stall with that cam. Link to comment Share on other sites More sharing options...
Sam (Bones) Posted April 23, 2008 Share Posted April 23, 2008 page 1, 3rd post Link to comment Share on other sites More sharing options...
kc8oye Posted April 23, 2008 Share Posted April 23, 2008 I'm running 2500 stall with 3.55's.. and a tall 1st gear (3.06)I could problaby get away with one.. but I'm VERY happy with the vac. secondary. Link to comment Share on other sites More sharing options...
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