Holley 4 barrel carb. How much HP+ ?

[Greddy]

Hi everyone, i have 4 barrel holley carb in 71's 240z. How much hp it approximately add?

P.S. sorry for my bad english

[Weasel73240Z]

I'm no expert on this, but I think most people on here would agree that running a Holley 4bbl probably doesn't improve power or performance with an L24 engine. You would probably make better (and more efficient) power with the original twin SU's.

[240ZMan]

I agree with Weasel73240Z. A larger carb will only increase power if the original was too small to provide enough air and/or fuel to the engine. In the case of our Zs, the stock SUs can provide more than enough air/fuel for a stock L6, and even for most modifications.

[Greddy]

So what is that carb for?

[MikeW]

So what is that carb for?

Big American V8 engines.

[240ZMan]

So what is that carb for?

A common problem with the SUs is that the throttle shafts wear out, begin to leak, and make tuning difficult if not impossible. Since new SUs aren't readily available, some have switched to 4 barrels (others to weber DGVs, etc). I've read of people who have properly set up small 4 barrels on Zs with good results. But they didn't achieve MORE power than with properly set up SUs.

If your setup is working well, then go drive it and have fun!

BTW, ZTherapy is a good source of rebuilt SUs that solve the leaking shaft problem.

[Greddy]

thanks for everybody for your answers.

Off topic. What are other ways to increase HP? My Datsun has performance exhaust system, does it increase hp?

[MikeW]

HP is increased either with more displacement (i.e., going from 2.4 to 2.8 liters) or by making the engine consume more fuel/air. Because the SUs supply exactly the right amount of fuel for the amount of air coming in you need more air. That's why bigger carbs don't help without the additional air flow. A different camshaft is one way to make the engine consume more. Polishing/porting the intake manifold can also make a slight improvement. The performance exhaust may help a little but it usually goes along with the other changes.

By far the easiest way to make the engine draw in more air is to force it in. The most common way to do this is a turbo charger. The simplest way to do that is to simply swap engines from a later model 280ZX Turbo. This has the added benefit of increasing the displacement at the same time. Another way to increase displacement is a new crankshaft. If you can find one the crankshaft from a diesel Maxima gets you from 2.8 to 3.1 liters.

[e_racer1999]

^must add to mike's post in regards to the crankshaft 'stroker' motor; it requires different pistons and rods to get to 3.1L. you would need 240SX (KA24) pistons milled down, as well as 240Z connecting rods.

[jmortensen]

Big American V8 engines.

You mean small American engines don't you? Can't run a big V8 off of a puny 390. It's a popular spec carb for 2.3L Pintos in dirt track racing.

I agree with 240ZMan as to the purpose of that conversion. If you've got a set of tired SU's and you've never heard of ZTherapy and don't know how to diagnose or fix SU's, a 4 barrel conversion can get the car running strong again. Probably not as strong as properly refurbished SU's, but well enough to make it seem like a big power increase over tired SU's.

[240znz]

Biggest performance gains are all down to head work. But you really should be thinking about modifications as an on going thing. You'll get very little increase in power by just putting a set of extractors on it. To get the best out of them you really need to look at the carbs, ignition, cam and head work upgrades together. They are all related one way or another. Careful and educated planning is the key. Read up all the tech articles you can and build a picture of what you are after rather than fitting parts in a piecemeal fashion.

One of the easiest mods to is change your diff to a 3.9 or 4.11. Just remember that that alone will increase acceleration but decrease top speed. Trade off's are everywhere.

[ozconnection]

I have an L28 that runs a Holley 465 on an Arizona manifold imported from the USA. Bought it off ebay. I also have a Clifford 4 barrel manifold for the 4bbl conversion. Very different results from each of them. The Arizona is a torque manifold by design. The Clifford sacrifices low speed torque for a lot more power up top all else being equal. Admittedly, the Arizona 4bbl needed a lot more 'tuning' of the carb to get it working right, but it's worth the effort.

I have played around with different sized carbs too, one being a spreadbore vac secondary 650, an annular booster square bore vac sec 600 and the 465 and they are all reasonable performers. The best for low speed torque is a close run between the 650 (small primary throttle bores) and the 465. The 600 produced the most power on the Clifford manifold. The 465 on the Arizona produces a low speed torque monster with a stock cam when the cam is also advanced (positition 3 on the stock cam sprocket). This is how my car is set up at the moment. Throttle response is excellent with the 4bbl setup and economy isn't half bad either. Like I said, it takes time to get it right but the results are there if you're prepared. BTW, I also recommend some mixture metering device to see where your mixtures are at. I use the Innovate wide band O2 sensor thingy. Best tuning tool I ever bought.

Check out my engine and car on youtube. (Dyno run Datsun 280C).

All the best with your 4bbl project.

Mark.