Hello all. Just wondering what the benefit is having a four barrel intake and carb vs. the two barrel set up. Does it really give you significant performance value? If so, how much?
With a dual exhaust system they'll make a noticeable difference, on a stock single exhaust, you won't see much improvement...
It depends on what you're putting it on (the build of the engine) Just putting it on a stock engine may do more harm than good, depending on what the intake and carb your putting on vs what you're taking off. There are larger 2 bbl carbs too that can give just as much of a boost as some 4 bbl intake/carb combos can yield.
Stock early 80”s 302 (5.0) with a cast iron 2V intake, 351 cam, and tubular headers can easy reach 180 HP.
I always start with the most restrictive portion of the entire "system" and work from their. If you look at the obvious trends that relate to maximizing overall engine efficiency?.. it's quite obvious that the internal combustion engine needs far more exhaust exit sizing than it does intake opening. Much tougher to build and tune any engine when there is an overly restrictive exhaust system in place.
'Gonna have to disagree with this. I ran a Holley 600 with a single exhaust for several years, and there was a noticeable power increase over the stock 2-barrel. Of course the addition of a dual exhaust system improved things even more.
anyone who's ever cut the Y-pipe apart on these kinds of exhausts will tell you where the biggest restriction lies. It isn't at the 2bbl carburetor.
Thanks for the replies guys. I gues my question is, what would you do to a stock 71 302 with dual exhaust in place to get more hp? Long tube headers, heads, cam, intake,carb? The car has 65k original miles and runs like a top but of course I want more hp.... Tranny is a four speed top loader with 3.0 gears one legger. Thoughts?
Gears!!!!! Compared to when I first got it, my Comet really woke up with the intake/carb/headers/gears
It's definitely restricted, but for a "seat of the pants" increase in power; slap on a dual exhaust with no other mods and you will feel .....nothing. Slap on a 4-barrel carb & intake, and you'll feel it plant you in your seat. That's just the reality of it. I know this from experience.
Times 3 on a gearing change. Then do the heads/cam/intake as time and money permit. The real bottleneck is the tiny assed exhaust ports in the stock heads. Next is the cam. After that's addressed, then the carb/intake combo can be looked at.
lol.. "nothing"?.. then either you fell prey to the cookie-cutter.. "that other car ran great so obviously mine will too" syndrome.. or you simply don't know how to design spec-built exhausts based on other engine design variables. It's not at all uncommon and everyone usually thinks bigger must be better. Usually much better to be slightly too small than much too big. The potential gain is 2-fold. You obviously gain back power by reducing pumping losses.. AND.. you fine tune the exhaust flows mass movement(speeds) and timing(rarefaction waves) for the specific combo(ie; 2bbl or 4bbl, cam, gear, etc). Exhaust has a lot of mass and helps pull on the intake charge to varying degrees and also reduces the force required by the piston to help push exhaust out at various rpms. ALL car engines, heavily muffled or not, benefit from that physical fact. In other words.. VE does NOT need to be over 100% before exhaust design becomes very important. Let me guess. You nailed the easy part of "reducing pumping losses".. by hooking up a tube header with 3" collectors suddenly downsized to around a 2.5" "high-flow exhaust" running crimp bends and chambered mufflers. A 3" exhaust would have just added insult to injury. Here's something to question. Where is it best to have the largest restriction in a airflow restricted racing engine when maximum VE is the primary concern. Under the carb?.. or at the exhaust flange? Why don't we just restrict them at the exhaust flange and keep running the bigger carb? At the end of the research and testing, most realize that the carb can be made to flow much more air than it was ever rated for(primarily due to it's lower test/rating pressure). Whereas an exhaust is often much trickier because it must essentially be tuned to vacuum the engines air mass into AND back out towards the atmoshphere more efficiently. That's why 390 nascar carbs can be pushed towards 550-600HP.. and 2bbl-class racing setups can reach even higher. Cam timing and exhaust tuning is key to making them work. Another misunderstood aspect is the exhaust heats impact on the gas dynamics. Air becomes lighter and speed can more easily increase before sonic choke takes place. This higher speed limit allows the total flow to counteract and offset the expansion process(need for even larger ports). That's why the "little assed exhaust ports" baddad mentions above can flow so much more air than similarly sized carburetor area.
Exhaust & the 4 barrel will sure help,but if you can stand it,GEARS are the ticket.Now you would`nt want to do this,but about 30 yrs ago,tells you how old I am.A friend of mine w/ a 65 stang,mild 289,toploader 4 spd,put a 5.14 geared 9 inch detroit locker,31 spline axles in the car.Needless to say,stop light to stop light it was a killer,no top end but it would snap your neck.Now you would`nt want to go that radical,but some 3.89s & overdrive trans would work wonders for your car.
I never "designed" anything. Back in the 1980s. '72 Olds Cutlass, 350, 2-barrel, single exhausts. 'Took it to an exhaust shop and had a full dual 2-1/4" installed after the stock manifolds. There was NO significant performance increase. Sure, fuel economy may have increased by 1 or 2 mpg. '73 Maverick, 302, 2-barrel, single exhaust (this was long before I had what's in it now). Installed a Holley 600 and Edelbrock Performer (not the RPM) intake, and nothing else. There was a noticeable power increase. Quicker acceleration and seat of-the-pants torque. It woke that little 302 up. All the theory in the world won't change what I experienced with these two cars. People are telling the O.P. that installing a set of duals will give him better results than a 4-V. Well, I say not so. It's bad advice. Should he put a dual exhaust system on his car? Absolutely, but that mod alone will not provide the performance increase he's looking for. It just won't. Obviously, you want to improve the exhaust, heads, cam, and intake. Compression ratio too. But if your budget doesn't allow all of those things to happen at once, then gears & a 4-barrel will provide the most bang for the buck.
