Ok, first, I want to run a mechanical fuel pump on my carb setup. The original engine is a 2.8L V6 (MPFI). Is there some kind of electric pump bypass available? Or will i need to replace the fuel tank?

Second, I did a calculation regarding the size of the carb I will need. I am looking a 600cfm Holley carb with vacuum secondaries, based on those results. I am installing a 355ci L98. I am assuming the maximum RPMs will be 6000 (based on my cam's advertised operating range). According to my calculations, a 600cfm carb should be enough to adequately fuel my engine (at 100% volumetric efficiency, which I know is not to be expected). Would there be any reason not to go with the 600cfm carb? And how does the smaller carb do as far as fuel atomization is concerned? I would think it will atomize fuel better if a 600cfm carb is operating at 75% of its max capacity: compared to something like a 750cfm carb operating at 45% of its max capacity.

I used this equation to calculate carb size needed, my friends tell me 600cfm seems small

(cubic inches/ 2) x (max RPM/ 1728)

any help would be appreciated

Thanks,
Steve

 

There is a sticky in the top section of this forum about converting the tank pick-up from in-tank electrical to engine-mounted mechanical pump.

If you're using a dual-plane intake manifold, it basically divides the carb in two, so the formula comes up a little short. A 650 would feed it a little better.

Any particular reason for vacuum secondaries, other than the old "VS with auto, DP with manual" half-truth?

What is going to be your primary use of the car?

 

Ok, I'll check out the sticky on the electric fuel pump question.

The car will primarily be used on the street. I want the car to be a fun, solid ride with decent fuel economy (and I'm not talking 30mpg either, enough to get me around and not blow a quarter of a tank getting out of the driveway ).

I do plan on using a dual plane intake manifold. So, the dual plane will basically be like running 2, 2 barrel carbs? I could see where I would need more cfm then. As far as choosing vacuum secondaries is concerned, that's actually the first time I've heard what you said about VS for auto and DP for manual. The car will have an auto in it, but you don't seem to subscribe to that little saying. Why do you consider it a half truth?

The main reason I chose the vacuum secondaries is because I want the car to be as close to emissions legal as possible, so the Holley 4160 series looked like a good choice. I've seen Q-jets (I believe they use manual secondaries) out there considered emissions legal, but I think they're up around 750cfm, and I don't want to over carb my setup.

Thanks,
Steve

 

Q-jets are air valve secondary, meaning a spring loaded air valve opens as air flow demand increases. Almost impossible to put it on too small of an engine. With a 350, you will be fine.

The "standard" line is to use a vacuum secondary carb with automatic transmission, and double pumper with manual transmission. The latter is true, the former is only true if you over-carb the engine. It would take about an 850 to overcarb a 350. Even then, the issue is the RPMs at which you go WOT for a given engine and carb size (the Holley website has a chart on that as well).

Holley has a spread bore 650 double pumper, List 6210. I had one on my Camaro last year, mileage was decreased and power no better (slightly worse) than it was with the q-jet. Admittedly, my q-jet is feedback computer control, so it should (and does) get slightly better mileage than a non-feedback q-jet.

Technically, no carb is emissions legal on an '88 model year f-body in the U.S. Enforcement is another topic.

 

ill throw in my two cents five7kid is definatley giving you some good advice and info, ill tell you my opinion though is to stay away from the 4160 holleys, i hate the singel feed, i love my 670 street avenger holley, its a 4150 series carb. get ya one of those great for street strip, good price, and the quck change VS springs is a good feature....