283 intake/exhaust combination questions

[rthuma]

I recently installed a re-manufactured 1962 283 in my 1954 pickup. I installed the cast iron intake manifold from the 1966 283 that I took out of it, along with a Rochester 2bbl carburetor that was on the truck when I bought it about a year ago. I had it dyno-tested and it generated 120 HP (@4400 rpm) and 186 ft-lbs torque (max @ 2,600 - 3,000 rpm).

It has the original CI rams-horn exhaust manifolds and a bolted together 2" OD pipe dual exhaust system without an x-pipe or h-pipe cross-connection. It is getting ~12.5 mpg around town and ~15.5 mpg highway.

The dynomometer guy suggested changing out the exhaust manifold to Corvette 2-1/2" CI manifolds and running 2-1/2" pipe/mufflers. He also suggested putting a 500 cfm carburetor on it. He thought these modifications would help the engine breathe better and improve the engine performance (more HP, not sure what he thought would happen to torque).

The intake manifold is set-up for a 2 bbl carburetor (small-spread bolt pattern), so I'd either have to put an adapter on it, or change it out to a 4-bbl manifold.

The engine power performance is fine for how I use it (every day driver). Better mileage performance would be nice. I have to do something to the exhaust, since one of the mufflers is pretty beaten-up.

Should I replace the exhaust system with larger exhaust manifolds and larger pipes?

Should I incorporate x-pipe or h-pipe cross-over?

Is it worth changing out the carburetor to 500 cfm?

If I do that, do I need to change the intake manifold, or can I use an adapter?

Does one change (intake or exhaust) necessitate the other?

Will either change have a bigger impact than the other?

Thoughts?

[protrash64]

I'd go with the intake and carb first. My experience with 2bbl's is bad gas mileage. My understanding is that some back pressure in the exhaust is not bad, and opening it up wouldn't help much in the case of your exsisting intake/carb combo.

I'd get a Performer intake for help in the low rpm torque band.

[rthuma]

Thanks ... Edelbrock 2703 Performer EPS intake manifold w/ 1404 Performer carburetor?

[jgarverick]

out of curiosity, what cam are you running? lots of performance can be had through modern materials, design and machining of the cam. slight increase in duration and lift combined with reduced overlap would give you a little power and some mileage.

[rthuma]

stock cams

[markeb01]

First up welcome to the forum. For a stock 283 the 2" exhaust should be just fine. An X or H pipe may build more low end torque, but I'm not sure you'd see enough difference with a stock engine to notice.

I would also change to the Edelbrock manifold and carb. The main disadvantage of the 2 barrel is there just isn't much the average person can do to "tune" the carb. An Edelbrock is easy to lean out or richen by changing rods, jets or both. A lot of adjusting can be done with the rods, which can be done easily on the engine.

The 2703/1404 would be a nice combination, and would allow retaining the original valve covers.

[jocko]

You mentioned "The engine power performance is fine for how I use it (every day driver). Better mileage performance would be nice." So, keep in mind that probably any dyno guy is gonna assume you want more POWER, not necessarily better mileage. If you are satisfied with your power, then I'd highly recommend a trans swap to improve gas mileage (to something, anything, with overdrive - be that a 700R4 or 2004R automatic or a T5/Tremec/TKO, etc manual trans).

But I'll take a leap here and assume you'd like to have your cake and eat it too. So, in that case, yes, a small 4 bbl with matched exhaust would be nice. To your specific quesiton, and most comments above seem to agree, if you mod intake, you get the most out of it if you mod the exhaust along with it. But I have to say, I agree with Markeb01 above - 2" is usually plenty for a 283 until you've made some other power mods.

If money is no object (HA!), here's what I'd do:
- o/d trans
- alum intake manifold and small 4 bbl (edelbrock performer (not the perf rpm) and a 500 cfm is a nice setup - I only mention "not" the rpm as your motor is mostly stock. Also, Summit Racing has some very inexpensive carb/intake combo packages that may be worth checking out.
- mild perf cam
- THEN exhaust to 2.5" once the above is done. (if you only do the carb, probably not much benefit to modifying the exhaust). An H- or X-pipe is a bonus, worth including in any exhaust system.

If money IS an issue - then maybe slowly work your way down the list.

I focused on your comment about perf ok, mileage could be better - and that's the Doctor's recipe for success. By the way, I am not a Doctor. If mileage isn't your number 1 concern - then skip the trans and go down that same list - pretty much in line with everyone else's comments thus far.

[rthuma]

Thanks to everyone above.

I didn't think to mention that the truck is riding on a '73 Blazer frame with TH350 transmission and NP 203 transfer case. Somewhere along the way, manual hubs were added, but no modification was made to the transfer case. I plan to install a Mile Marker shaft replacement kit on the NP 203 so it will have true 2WD capability, which should improve the mileage.

Jocko - I'm not sure if that would influence your transmission comments above, but in any event you've all given me a great list of prioritized improvements ... I probably won't ever add up the costs because it is more fun to pretend the truck only cost me what I paid for it.

Sounds like an intake manifold and 4 bbl carb are in the near future.

[LeftCoast32]

I just finished the exhaust on my '66, here is what we did.

Stainless Steel Block Hugger Headers - 1 5/8" Primaries and 2 1/2" Collectors

Stainless Steel Mandrel Bent 2 1/2" Dual Exhaust

Stainless Steel Mufflers x2

Dumped exhaust right before rear axle

It sounds real good but a little quieter then I wanted. I hope that as they break in they will get a little louder.

I will be installing a Offenhauser 3X2 Intake with the Rochester Carbs.

I currently have the stock single Rochester carb and noticed a slight improvement in mileage. My old exhaust was falling apart and was like open headers so not a good comparison.