first gen k5 with 250

[k571]

hey i was wondering going from my old 1 barrel monjet to a holley 350 cfm carb, is threr going to be great deal of notice in my performance? curious does anyone know what tranny they put in 71 k5s its 250 straight six with 4 speed tran! any help would be swelll it also just had the valves redone so she screams, so i would have thought it would gain some more power or do i just lose aloot more in gas mileage?

 

[Blazer1970]

Tranny is an SM465. I would not expect much if any power improvement from that carb swap. It really depends on how well the engine is tuned and running before and after the carb swap.

 

[diesel4me]

Same intake??

If your adapting a 2 bbl Holley onto the stock 250 intake,you might notice better acceleration,and more pep..but the valve job will probably give just as much a boost,if not more..a 4 bbl intake (aftermarket) is available for the early 250's with the "non integral" head design,and a 390 CFM Holley 4BBl carb works good together,or with an adapter, a 2BBl carb can be used..

Be aware the more gas you pour in,the more needs to get OUT of the engine too..most intakes are sold with the intention of adding a header too,and some reccomend a hotter cam grind to further enhance performance..

I had a 600 CFM Edelbrock adapted to my 79 250 six that came with a 2BBl "Vari-Jet" carb originally..it had the integral head(intake cast as one with the head)--I made an adapter and spent two days making throttle and kickdown cables work..it actually drove much better ,it no longer felt aneimic...had more low end power..

I did end up disconnecting the secondary butterflies linkage,so in effect I made it into a 2 bbl..it never needed all 4 barrels,in fact,it slowed down when I opened them up--it actually ran better on the primaries only..a six doesn't need very much air or fuel to run right..they WILL guzzle gas as fast as a V8 if you put too large a carb on them..

 

[3 on the tree]

hey i was wondering going from my old 1 barrel monjet to a holley 350 cfm carb, is threr going to be great deal of notice in my performance? curious does anyone know what tranny they put in 71 k5s its 250 straight six with 4 speed tran! any help would be swelll it also just had the valves redone so she screams, so i would have thought it would gain some more power or do i just lose aloot more in gas mileage?

The first thing I have done to my 70 250 K5 is swap in a HEI distributor. I immediately noticed a positive effect power wise. One guy who races 250s back east told me to get a 292 3 bolt flange exhaust manifold. He claims only a 1/10th difference between it and a header. Back in the late 60s, Mercurey Marine put 230s in some of their stern drive boats. They came with a twin one barrel intake on them. I am still looking for one for my Blazer.