i have a 350 from a 3/4 ton chevy truck in my car, im pretty sure it has the dish top pistons and the smogger heads. well i also have a good lg4 305 with really good shape heads. i was thinking i could just use the stock 305 heads and put em on the 350 and raise compression and then install an aftermarket cam. how much more power if any would this give me? the only mods i have is a 305 aluminum intake, edelbrock 600 cfm carb and open element, headers, and 160* thermostat. the car is a daily driver and im pretty short on cash so i figured instead of letting my good 305 heads go to waste, i would put them on my 350 and get a good cam off of ebay or maybe get a slightly used one someplace. what would be a good cam for this? thanks alot

 

They will raise the compression ratio to about 9.6:1 with a felpro .040" head gasket.

Use a small torque-y cam
A cam with 214 or less .050" duration will be just right.


Will add noticable low the mid range power just what you need for a truck or mild "daily driver" build up.

if you want some more top end hp give them a home porting and have a machine shop install new larger 1.94 intake valves before you bolt 'em on..

This head swap works really well for what you have in mind.

 

try the summitt cam k1102 or 1103 I ahve the 1103 and like the torque and topend power I have with this cam. Definately port the 305 heads though and up grade the xhaust without those upgrades a cam will do little good without porting the heads and opening up the exhaust the lg4 exhaust chokes these engines. A cam is nice but if the exhaust has no place to go will the cam be doing you any good.

 

before bolting them on, i would install larger valves, new valve springs, and new valve seals...

while the valves are out, port them if you are comfortable doing so... if not, then leave the porting out...


this will work for what you want, but of course you would make alot more power with some better flowing heads......


oh, and the summit #3 cam works great for mild daily drivers..

 

i was going to home port them but i just done have the time or the money to do that. how much would larger valves and springs cost me? i dont really care about top end since it is a daily driver, i never get it over 65 so i was really looking for better low end anyway. will it really give me that much more low end to port the heads? if it does then i might save a while longer and get it done. thanks alot

 

call your machine shop for what they will charge ya...

if this is a pure daily driver, it might not be worth it to you if you dont do it yourself.. the cost of having it ported vs the result wouldnt be worth it to you.

 

top end means top end of the rpm range, not speed range. Gearing can change where you are at rpm wise relative to your speed.

 

If all you;re really looking for is to add some low/mid punch
and are not interested in horsepower ( speed)
then you could just bolt them on.

 

how much more power will i get, like hp wise if i put larger valves and different springs on the heads? i think i am going to use that number 3 cam from summit. i found a kit on ebay for larger valves on my heads and stiffer springs and it will cost about 160 bucks. but it is complete with everything to redo my heads. so i figured if it will be worth it then i might as well just redo the heads for 160 bucks

 

You should expect a minimum of 25 to 35 peak horsepower gain.
from installing larger valves and porting the 305 heads.

Porting will help the top end more than the low end of the power band.

A modest porting job (simple pocket porting) will get you modest results, Depends on how far you're will in to go.
You cannot make these heads too big.
The better the rest of the combination is, ( exhaust system etc)
the more gain you'll get.

 

Bad TA. Before you buy anything look for the valves and springs here www.enginekits.com

 

If you don't use forged pistons and hot fuel,you will break the ring lands off the pistons. I've got a 355 on the stand right now that met a very early death because of this combination. If the heads have been resurfaced the chambers will be too small/compression too high. I checked my 305 heads and they were about 56cc/58cc. This coupled with the flat tops........you get the picture. It rattled like a can of marbles not matter the fuel or timing. It did run like a striped ape....for a little while. Good luck.

 

his engine has dished pistons. his compression ratio with the 305 heads will not be near as high as yours, with flat tops.

One of the key things to do to cheat the motor into not being so detonation sensitive is to get the quench right.
this is most critical with higher compression ratios.

some/ many flat top pistons are .045" (or more) in the hole on a stock block.
that combined with a .040" head gasket yields a .085"+ quench distance.

getting the quench distance right at .038" to .040" really makes a big difference.

back "intheday" when GM built real high perf carbed SBC motors with high compression ratios, the factory pistons were .025" in the hole and they used .015" thick gaskets. Total quench =.040"

When you use a .040" felpro replacement gasket you throw this quench distance off. (unless you "0 deck" the block to compensate) When you combine that with common replacement flatops like h345np's that are .045" in the hole you really mess it up.

Useing colder non projected tip plugs helps too.
Like champion RV8c instead of stock AC R44 or 45's

A recent project I did with mega shaved 305 heads on a decked 350 had 12.65:1 measured compression ratio. 240 psi cylinder pressure
a very big cam and polished chambers and very tight quench clearance (.035") Never heard any detonation and no problem with the thin head gaskets.
A piston ring land failed too (cast pistons) but not because of detonation.
The ring gap was just a little to small for the application.
The ring butted.


The bottom end was not built as a race motor. (it would have had wider ring gaps) Also went like a "raped ape"

Going to rebuild it this winter with bigger ring clearance and try again.