305 heads onto 350

[peter redman]

was wondering what kind of effects puttin a set of 305 2 barrel intake heads on a 350 with a 4 barrel intake. the 350 is stock other than a rv cam.i'm told the compression will jump up. nobody seems to know the final ratio,maybe 9:1 or 11:1 is what i've been told.will thiis effect the lower end performance.the blazer is used mostly on the street with mild towing.when the bush is entered the slow speed rock crawling is mostly used with a mud blast seldomly happening.the 350 heads need a rebuid and the 305 heads are fresh.so what do you think ??

 

[beater_k20]

dont waste your time with 305 heads on a 350. the smaller chamber heads will up your compression, and you will need a higher octane fuel. the smaller ports on the heads as well as the smaller valves will both hurt the performance, cancelling out any power you picked up from running the higher compression.

 

[4X4HIGH]

Based on a 4.00" bore and the 3.48" stroke, assuming a piston valve relief of 6.25cc's, a deck height of .020" (4.11cc's) with a .038" (7.83cc's) compression head gasket, and a 76cc head your compression would come out at 8.6:1

Now with everything the same but changing to a 58cc 305 head your compression would jump up to 10.4:1.

Basically your swept volume is 716.62cc's and your total chamber volume is 94.19cc's with a 76cc 350 head you must add the swept volume and the total chamber volume together then divide that number by the total chamber volume to give you your compression ratio.

Your total chamber volume assuming a 58cc 305 head would be 76.19cc's so the same math applies.

 

[Hogback Fabrication]

What beater_k20 said, don't bother. 305 heads have a smaller combustion chamber which will raise your compression ratio (increasing both power and economy, but requiring you to run premium fuel). 305 heads have a serious downfall though, they have tiny valves and intake runners which will undoubtedly lose you power. You will probably make less power with 305 on a stock 350 (even on premium fuel) than you would on a stock 350 with stock 350 heads.

 

[primerk5]

I did this on my 350 cause the heads that were on it developed a crack. There was a Van Up the street at my local fire station that they were going to use to practice on. We got to it first and removed the heads from it. It was a 305. Had them cleaned and put new seals in them. Thats it. After I put them on my truck I would have swore it had a slight more get up and go than it had before. I don't understand why you would have to run premium fuel. I d'nt and never have. It runs great. burn 40 in tires without thinking about it and My motor is pretty much stock. Q-jet carb rv cam stoke everything else(just rebuilt.) I'd say do it. Thats just my opinion.

 

[Slapperbar]

No need for premium. I have some 305 "claimer" heads on my S-10. 2.02/1.6 and worked runners. They need new guides now thou.

 

[longbedder]

It would depend alot on which pistons are used. With a dish piston you'd probably be OK. Flattops or domes = maybe too much compression for 87 octane.