Thread: Bill Mitchell Hardcore 870 carb

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Guys,
My 468 currently has a Weiand 177 supercharger with a Hardcore 870 double-pumper (80, 87 jets), Merlin heads and a Turbo 400. I know I'll never get "good" mileage with this setup, but I'm turning a drag car into a street car and was wondering if I should keep this carb or move to something with vacuum secondaries. I'm learning the "blower" stuff as I go, but definitely don't want to go too lean and burn things up. I would also like to keep the blower, if for no other reason than it adds decent power and makes me different from the average BBC cars. Any comments from those who have experience with these types of setups?

As always, I appreciate it.

Hobo

One of these would help you tune till its perfect and give you the info you need so you dont burn it up.

http://www.edelbrock.com/automotive_.../6000/6593.pdf

yup if you run it hard and you lean it out you will have bad things happen you can try going down on the jets about five down run power valves if you have power valves then leave it alone or try what denny said with a vac carb but how much stall and gear is hurting your MPG i bet more then any thing???? if running on the street you can still have a runnner with out to much gear i am running a 3.89

I had a bbc 410 with B&M 174 blower,almost the same as yours,I ran a holley 3310 front power valve,I added a secondary metering block for more adjustment,ended up with 70's front,78's rear,got 13mpg on highway,drove it 150 miles round trip to the drag strip every week,ran in street class,ran high 11's,turbo 350 trans,3.42 rear gear,I ran this combo for 4 years,switched to 8-71,with two 750 dp,really sucks gas now

i did get about 15 MPG with mine if you keep your foot out of it was a bit on the lean side i fatten it up at the time i was paying 3.50 for race fuel may go to alcohol or leaner back down hate to see how much the fuel will be this year may have to buy it by the barrel

Thanks guys. I forgot to mention I'm running 4.10s and about a 2800 stall (Coan built it for my setup, so it's a little hard to tell since I haven't had it on the road yet - shortening the driveshaft because of the TH400 install). You're right Pat, a lot of my mileage is going there.

Originally Posted by hobo

Thanks guys. I forgot to mention I'm running 4.10s and about a 2800 stall (Coan built it for my setup, so it's a little hard to tell since I haven't had it on the road yet - shortening the driveshaft because of the TH400 install). You're right Pat, a lot of my mileage is going there.

If this is really a street car 4.10 is too much gear,unless you never go down the highway,convertor sounds ok for street,I am running 3.70 gear in my strip only car,blown big block makes monster torque off idle,no reason to run 4.10,

I agree, but they came in the car and I'll run them until I address the other issues first ($$). I do very little highway miles. In the '68 Camaro I ran 3:73s, which seemed to be a good "middle road" for street and strip.

I'm not hearing terribly convicing arguments to NOT run the Bill Mitchell carb I have now, so I guess I'll dyno the car locally and have the A/F ratio checked so I know I'm running a safe mixture at WOT. TH400s seem to like vacuum secondaries, but blowers seem to like double-pumpers (GAS) to keep the mixture rich. Since I usually shift the car ratchet-style, I guess I'll lean toward keeping the pumper.

Thanks everyone. As always, your comments are very much appreciated and respected.

Hobo

Originally Posted by hobo

I agree, but they came in the car and I'll run them until I address the other issues first ($$). I do very little highway miles. In the '68 Camaro I ran 3:73s, which seemed to be a good "middle road" for street and strip.

I'm not hearing terribly convicing arguments to NOT run the Bill Mitchell carb I have now, so I guess I'll dyno the car locally and have the A/F ratio checked so I know I'm running a safe mixture at WOT. TH400s seem to like vacuum secondaries, but blowers seem to like double-pumpers (GAS) to keep the mixture rich. Since I usually shift the car ratchet-style, I guess I'll lean toward keeping the pumper.

Thanks everyone. As always, your comments are very much appreciated and respected.

Hobo

for that you have i think you will not see much with a vac sec sitting on top of a blower but you could see if some one had one to try ? .i was thinking you were pulling my leg a blown big block with 411s 2800 stall and your worried about MPG??

I was only worried about things turning into "gallons-per-mile"

Thanks Pat - You're definitely one of our big block gurus and I thank you for taking the time to respond. As for pulling your leg, I'll try that some other time during this project!