B4B vs. SP-1 and a quest for mileage..

Here's my real world findings. The car is my 71 Lark, 470 with stage 2 heads, level 1 porting. 290h cam and 10.6:1 compression. M22W trans and a 3.50 gear. It's gone 11.50s at 120. The car weighs 3900 lbs. The 60' times are 1.7x, once I got 1.67. These times were with a 4.11 gear.

Anyway, I wanted to return the car to a more street friendly ride. I know I won't be to the track anytime soon. I commute about 30 miles each way for work averaging 50-55 on country roads. With the 1000 cfm holley and 4.11s the car would get about 7-8 mpg. This was hard to justify. Swapping to 3.50 gears jumped the mileage to 11-12 with no other change.

Over the weekend I swapped a B4B in place of the SP1. I was going to put the Q-jet on too but decided to see if the dual plane would be worth any mileage over the SP1 so the Holley stayed.

The car is much more pleasant to drive. The increase in bottom end power is very noticeable. I can lug the engine down below 1000 rpm in 3rd gear going around a corner and accelerate out smoothly. With the SP1 I would have to be in second to keep the rpms up going around the same corner. I can cruise 30-35 in 4th gear around 1300 rpm.

Initial guesses on the mileage show an increase based on how far the gauge normally moves for a work trip.

The car is more responsive as well. I know i gave up top end hp and gained bottom end. I think it was worth it. Any quick stab of the throttle nets tire smoke and the rev limiter with either intake so it's hard to notice the top end loss..

On the street I say the B4B is the winner. Definitely if you have a manual trans. I know an auto trans with a loose converter might not notice such a difference.

If only there was a high rise dual plane available..

 

Got any pics of that engine bay?

 

So will the updated Eddy performer do just as well?

 

Now put on a well tuned Qjet and you will see even better mpg and you will get a lot better street manners plus a well tuned Qjet will work when you hammer it.
On one of my 4 speeds years back I had a 850 DP and the car was so annoying driving under 50 mph, because you had to be on the pedal all the time. Switching to a well worked Qjet it became a whole new car and were so relaxing to drive.

 

If you really have long term plans to drive it that many miles daily I'd go right to a reasonably priced self-tuning EFI setups. You may have lost top end power but you may find that the dual plane intake may recover quicker off the line at the track. I agree, too bad there is not an RPM Air-Gap intake.

Sticks are great fun on the street but not really the best way for good 60's at the strip unless you really, really, really "beat it like you stole it".(Think Stock and Super Stock classes.) Not for the faint of heart. A long time ago I ran a stick in a Camaro and when I got up to popping the clutch at only 4000 rpm the whole rear of the car felt like it was going to break off and that is the maximum I ever took it to although it could have used more. Not really a serious effort car so I'm sure more suspension work could have helped but you still have to wing the rpm to get them to launch.

 

High-rise dual plane...do you have room to stick a 1-2” divided or 4 hole spacer plate in there?

 

I do have a 1" spacer under the holley. I have the stage 2 scoop so there is lots of room.

I'm definitely not going to swap to any of the generic efi stuff. I've got a well worked q-jet that i'll swap back on.

 

I done a qjet for my orange car years ago that I swear had the smoothest fuel curve ever it was a hodgepodge of qjet parts but man did it run nice,...ran like EFi ,...I'm about 10 yuengling into the evening btw ha

 

If the injectors aren't below the throttle plates you ain't gaining.

 

Just about any carb you put on there will get better mileage than a 1000 DP. If you have the the Q-Jet then it will surely be a noteworthy improvement. IMO a monkey with a squirt bottle would probably get better mileage than a 1000 DP.

If you want real carb mileage find a Thermoquad 9800 or Competition Series 850. That is the ticket.

 

With some mopar adapter plates and a valley cover, a high rise dual plane ( performer rpm) is possible

 

We built a 90 so pick truck....removed the 454, installed a 502. Nice afr heads, roller cam, close to 600hp i would guess.....has 1000 cfm holley, 3.73 gears and th400.....it regularly gets 14mpg on the highway and 10 around town

 

On the highway where throttle movement would be minimally changed would be the DP's best chance, no doubt. Are you saying it is doing better than a Q-Jet or another non-DP carb?

 

I thought about that. Lots of $$$ at the end of the day though.

 

Our intakes were designed for wet flow.
These new efi units work really well. Even w the injection up top. From street to strip.
I’m just stuck w carbs for now myself. Have friends enjoying their efi quite much now.
I need to get back to getting a qjet right.
So far a couple gurus have been thru mine. And really disappointed.
Hopefully you have some good results.

 

I am utilizing the mopar adapter plates and a high rise cross ram with two 850’s. All of it will be on top of Stage 2 TE heads. I won’t be driving it as much you drive yours, but it will be fun when I do.

 

Quick update- I got 11 mpg again with the last tank. I was expecting more with the b4b, as its running smoother, but i also drove it pretty hard getting a feel for the new intake. It may do better if I drive like an adult.

 

What are you doing for the water outlet?

 

I ran a b4b with an 850DP and typically ran about 12.5 mpg driving nice. When I switched to SP1 I really didnt see a change except for it cut my E.T's a bit. I never found the bottom end to feel sluggish, but my 60 foot times did slip by about .05 sec.