Are ther any pros and cons to a spread bore vs a square bore.I,m looking at buy a intake for my vortec heads .I now have a spread bore holley that I will eventullay replace with a bigger one in a 750 range.If the diff.between the two are minimal and the option open I,d stay with the spread bore to save some money now. Good wrench crate vortec heads cop cam 268H Elderbrock performer Rpm
Keep in mind that Edelbrock doesn't make a Performer RPM Q-jet intake for Vortec heads. Unless they've introduced one in the past year or so, since the last time I asked them.
I was always told that carter/edelbrock are easier to tune and stay tuned. Holleys can make a couple more hp but are more finicky. I have still haven't figured out the black art of carb tuning. I have owned both and they seem similar to me.
Really easy answer... Almost all spreadbore intakes are drilled for both patterns and work equally well with both types. Squarebore intakes are only drilled for squarebore carbs, and adapting a spreadbore to a square intake is not a wise thing.
Spreadbore intake = the ability to use either carb
Squarebore intake = pretty much just a squarebore carb.
Spread bore holley were made to replace a Qjet directly to a Stock Qjet manifold.
You cannot mount your spreadbore carb to a hi rise RPM style vortec manifold without a adapter.
The only spreadbore/Qjet flange "vortec" manifolds are the low rise design.
You wan the hi rise design.
Sell your spread bore carb and get a Edelbrock #1407 carb and a RPM vortec manifold. For every seller, there is a buyer that wants just what you got. You can find these Eddy #1407 750 carbs in near new condition for as little as $100 in Craiglist. Kijiji and ebay.
You'll find that 750 carb/rpm vortec intake combo works pretty good.
In reguards to carbs they both have pros and cons. You typically "can" get better MPG around town with a spreadbore but it depends on driving habits and the particular rig. I kind of prefer squarebores for a couple of reasons. One I think that some spreadbores begin to dig into the secondaries too soon and if that happens all better MPG aspirations are out the window. It is possible to get good MPG with a squarebore as well, but youve got a bit more foot available before you need to transition to secondaries. I find this particularly useful for truck/towing applications or heavier cars with auto trannys.
Another thing is that squarebores are easier to "transition tune" and the transition to the secondaries is almost always smoother. If youve never driven a lightweight manual trans equiped ride with a mechanical secondary squarebore you really should try it. They make an awsome marriage.. That combo gives new meaning to the word responsive.
Lots of people using vacuum secondaries and autos thesedays though and that is a real good match too.
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