Hello, my dad has a 1951 Chevy truck and is going to be putting a 350 in it from an '84 van. It is a bone stock 350. I have a 305 out of a '79 Camaro, bone stock also. We have read where putting the 305 heads on the 350 would be a cheap upgrade. Is this worth the effort? The only cost would be the headgaskets. He plans on putting a Holley 650, performer intake and mild cam in the 350 anyways so would be half way there to remove the heads. Thanks in advance for any advice!! BTW, I have searched and read other post, but most talk about the 305 HO heads from the '80's. These are the stock heads from the '79 305...smaller valves from what I have read.
I did this many years ago on a Nova I used to have. The combination worked out ok. It ran well and made good power. The 305 heads I used had a smaller combustion chamber than the 350 heads that were on the motor originally so it bumped the compression a little. The downside was the heads also had smaller valves so that was a bit of a disadvantage. I think there are two sizes of intake valves used on some of the 305 heads from that era. Some have 1.72 intake valves and others have 1.84. I would't do it with the very small valves. Jay
I have been running a set of 305 heads on my 350 in my 72 Chevy pickup for 5 years now with no problems at all. If anything, it gave it more bottom end torque. My 350 heads were cracked so I acquired a set for free and replaced everything on them.
What about using a thinner head gasket or steel shim to bump up the compression of the 350 heads? They'll breathe a lot better than the 305's. If you're determined to use the 305 heads run the numbers and see what you've got first. Click here: Small Block Chevy Cylinder Head Identification
More compression = more torque. Smaller valves = less horsepower at high RPM. 84 350 is only about 8 to 1 compression. IMO swapping the heads will raise the compression to slightly less than 10 to 1. With the Performer intake and an "rv" grind cam and setting the timing @ 32 total (due to the higher compression ) it will make a great package for a heavy vehicle. Go for it ! Dave
for putting in a truck use the 305 heads with the 1.84 intakes if you can. the 1.74 will work too. as stated before the smaller valves will give you better low end grunt. just what a truck needs. will help in the gas mileage also. as for using the thin head gaskets it will not help you that much. but i use them all the time any way. if you really want to see an improvment do a good valve job as in 3 angle with bronze wall guides. i could never see the point of putting a used head back on another mortor.
Don't the 305 heads vary in CC's from 53cc-58cc? Before guessing at the compression ratio shouldn't you go to an actual calculator and figure it out, thus avoiding detonation?
I am going to pull a valve cover today on the 305 and make sure which heads I have. I am guessing that is the only numbers I need? The 350 is in a different location now so can't get any number off it anyway.
Look at the casting numbers on the heads. If they end in 416, they are 58cc chambers. If they end in 601, they are 53cc chambers. The 601's on a 350 will be into race gas territory. Pay real close attention to the quench area clearance. Measure the piston below the deck and use gaskets that get you into the 0.040" to 0.050" range, but not closer or further. That will be the best detonation control (ping) quench. Further than that and you get premature flame invasion and a lot of ping. Less than that, you get possible contact as the bearings wear and carbon builds up. The 1.84 valves are fine for street duty. They'll get you to 5000 on a good day. They need a good seat job and the valves themselves are only cut one angle, so have them back cut to 3 angles. You really need to take the die grinder the bowls. The throat cut from GM is sloppy and leaves ridges. Just clean that up and they are good to go. The exhaust side is the weak bit. Detail that bowl and open/smooth the radius and they will flow fine. You can likely leave the 350 cam in place and just go to 1.6 rockers if you only want a bit more lift. The runners are tight, so adding cam may not get you much? The tight runners make for excellent torque, so don't be concerned. I'd shoot for 416 heads for the street and cheap pump gas. They will put a smile on your face Oh, hold the T-Stat to 180* so you don't crack one.
race car engine builder talked me into 305 heads. his line was, don't let any one tell you they don't flow! we clean 'em up like this and this polish the domes -x-aust side,and bowls. 1.94 valves 3-way yada yada............. well I love my set up, 10+ CR, run pump gas, great MPG, got $250 invested!!! heavy car, runs mid 14 sec. and gets 20 MPG
Well the casting is 376450. Looks like 60cc chambers, but I am getting conflicting info o the valve size. Some say 1.72/1.5 and some say 1.72/1.3.
367450? http://cgi.ebay.com/ebaymotors/305-5.0-CHEVY-cast%23450-REMAN-CYLINDER-HEAD_W0QQitemZ250536598540QQcmdZViewItemQQimsxZ20091126?IMSfp=TL0911262010022r6654
Of course i put the valve cover back on now, but I think it was 376450...Must be a typo in the Ebay add here is what mortec says: 376450.....75-81...262/267/305..6 or 7 exhaust bolt holes, 60cc chamber </pre>
My mistake. I'd go with Mortec, I forgot about them. Looks like the other link I sent you as well as Ebay are typos. Sorry about that.
So am I correct that worst case scenario the 305 heads would flow as good as the factory 350 heads on the engine now but produce a higher compression engine?
A lot of it depends on what kind of driving you'll be doing. The smaller valve/port will help the velocity of the fuel/air mixture, which helps pack cylinders. This is something you'll "feel" around town, light to light. Above 4000 RPM(?) the 305 heads will drop off in performance for the same reason (small valve/port). BUT, 4000 RPM is seldom seen in "driver" cars. Put a cheapie SP-2P intake that most people hate, and you'll really have a snappy sonofa***** in the lower, street friendly RPM range
KEV...there is no problem putting smaller heads on 350 blocks. that is for stock expections, don't look for big time performance thow. and i don't believe you do...POP.
What about the fact that it will make the engine detonation sensitive with compression ratios over 9 to 1?
That is exactly what we are looking for. Something the has a little more pep than the stock 350 for a small amount of money. I can't see us going above 4000 rpm regularly. We already have a brand new Performer intake and Holley 650 vac sec. carb and headers. Then plan was stick the 305 heads on and a small cam and drive it.
Yep, not looking to blow the doors of anyone that's for sure. Just want something some respectable pep around town and for little money using what we already have.
OK, to calculate the compression increase, we need to know what heads you have on it now? The best general street improvement going to 305 heads on a 350, is with the 416 castings. If you have open chamber (70+cc) smog heads on the 350, the 416's will wake it right up. The 1.84/1.50 valves are plenty big enough for general street work.
Unfortunately I don't have the 350 at this location,but it is a stock 350 out of a 1984 GMC van so I would ***ume 76 cc heads?? As stated above, we already have the 450 heads so we are not looking at buying different heads. We are just wanting to see if by using what we have will increase throttle response around town. BTW thanks to everyone for all the input so far....it has been very helpful.
that 1984 350 WILL have dish pistons, and therefore you will NOT have too much compression with the 305 heads. It'll be nice and snappy. Enjoy. I'd be tempted to leave the stock cam in it
I was thinking it would have the dish pistons also. So you think the stock cam would be ok to leave in it? I just figured a step up on the cam might help performance but if it would not make that much of a difference then it would be money saved and not have to worry about cam break in.
Yes, I'd leave the stock cam in. A tiny bit difference in cam would not be noticeable. And a bigger difference in cam design would lessen the snappy, lower RPM performance for what I believe you're gonna use the motor for
Sounds like a plan. Now the next question. Anything I could do to make them perform a little better? I have a dremel and a die grinder is it worth the effort.
The Jalopy Journal
