possible 350 with 305 heads. looking for help on if i should

[Mohawkman]

hey guys this is my first thread ever so bare with me. i have a 73 k20 th350 with 4.10 gearing. going to be running 900r16 ( 36 inch military tires). The engine in it when i bought it was a totally gutless. it was supposed to be the original 350. turned out to be a 88-94 305 with an old set of gen 1 heads on it. so i picked up a 350 4 bolt out of a 72 camper special. so i was wondering about putting the 305 heads on to boost compression. they are the 416 casting. the cam kit that was in the 305 has new springs in the heads with new push rods and lifters. the cam is comp cam 12-206-2. wondering how this combo would work for me. the truck is used as a daily driver in the winter and a tow rig and some off roading in the summer. thanks for any help

 

[SkinnyG]

305 heads on a 350 was an old school way to boost compression.

LOTS of discussion on LOTS of forums about NOT doing it, and a number of people who think it's fine.

I ported the snot out of a set of 305 heads, and have them on my 350.

If the 350 has dished pistons, your compression will increase to a reasonable level. I have flat tops and a 0.015" head gasket, and mine works out to 10.9:1 compression. I also run a fairly "non-truck-oriented" snotty cam, so the added compression is good.

Advantage: The 416 heads are a good casting to use.

Advantage: You have a truck. More power from better heads will be more noticeable above 4500rpm. The smaller ports and valves are fine for torque and truck.

Nutshell: Will it work? Yup.

 

[Mohawkman]

Thanks for the response. So you think that cam profile and heads would be better for me than the stock set up?

 

[Green79Scottsdale]

Thanks for the response. So you think that cam profile and heads would be better for me than the stock set up?

The cam will definitely be better than stock.

The heads are another story. This is what I believe about the 305 head debate. Putting the stock 305 heads on a 350 for more compression is a waste of time. Yes, you DO raise your compression. But in STOCK form they have worse air flow than 350 heads. Now... as SkinnyG did... a set of ported 305 heads can actually flow the same as the glorious Vortec heads! So if you are going to run them 416's, make sure they have a good port job, otherwise you are wasting your time. I would rather have bad compression/good flow than good compression/bad flow, relatively speaking.

305 advantage: higher compression.

350 advantage: most likely better flowing due to bigger valves and slightly bigger runners.

How much of a budget do you have? I would suggest looking on your local CL for some heads that are better than either of the ones you currently have. I just ran across some World Products on my local CL for $300/pair. Those would be better than either of your heads. Just another option to think about.

 

[Mohawkman]

The cam will definitely be better than stock.

The heads are another story. This is what I believe about the 305 head debate. Putting the stock 305 heads on a 350 for more compression is a waste of time. Yes, you DO raise your compression. But in STOCK form they have worse air flow than 350 heads. Now... as SkinnyG did... a set of ported 305 heads can actually flow the same as the glorious Vortec heads! So if you are going to run them 416's, make sure they have a good port job, otherwise you are wasting your time. I would rather have bad compression/good flow than good compression/bad flow, relatively speaking.

305 advantage: higher compression.

350 advantage: most likely better flowing due to bigger valves and slightly bigger runners.

How much of a budget do you have? I would suggest looking on your local CL for some heads that are better than either of the ones you currently have. I just ran across some World Products on my local CL for $300/pair. Those would be better than either of your heads. Just another option to think about.

Budget is as little as possible just wondering about using what I have. I was under the impression that the flow of the 416 heads didn't become a problem to you hit 5000 rpm? Which I never intend to do.

So swapping in the cam would be a better choice either way?

 

[Green79Scottsdale]

Budget is as little as possible just wondering about using what I have. I was under the impression that the flow of the 416 heads didn't become a problem to you hit 5000 rpm? Which I never intend to do.

So swapping in the cam would be a better choice either way?

Yes on the cam either way.

The heads could go either way to be honest. Do you know exactly what heads are on the 350? What cc chambers are they? Maybe going to the 416's won't yield any higher of a CR. Some 305 heads flow better than 350 heads, some don't. Get accurate numbers for a true CR. Maybe the small chambers in the 416's will put you at too high of a CR. I guess there are a lot of things to take into consideration. Overall, you probably won't go wrong with either one!

Depending on what casting the 350 heads are, I would do some home porting on the 416's and have them machined for 1.94/1.6 valves. There are lots of good threads on thirdgen.org about the 416 heads.

 

[Mohawkman]

Yes on the cam either way.

The heads could go either way to be honest. Do you know exactly what heads are on the 350? What cc chambers are they? Maybe going to the 416's won't yield any higher of a CR. Some 305 heads flow better than 350 heads, some don't. Get accurate numbers for a true CR. Maybe the small chambers in the 416's will put you at too high of a CR. I guess there are a lot of things to take into consideration. Overall, you probably won't go wrong with either one!

Depending on what casting the 350 heads are, I would do some home porting on the 416's and have them machined for 1.94/1.6 valves. There are lots of good threads on thirdgen.org about the 416 heads.

Thank you. I don't know what's in the 350 it's stock 72 engine. But I have never had the valve covers off it. Thus is a summer project so I'll have do some digging into it then. Thanks for the info guys.

 

[SkinnyG]

You could post a picture of the casting marks on the end of the heads. Typical heads have typical patterns.

I used the 305 heads on my truck because they were free, and needed zero (and I mean z-e-r-o) machining - the valves and guides were actually ON spec - and I ported them myself (hours of my life I will never get back).

If you are going to throw money and machining at heads, either just buy Vortec heads, or something aftermarket. I would not "rebuild" a stock 882 head at all, and I would throw NO money into 305 heads.

I am very tempted to try a set of Engine Quest CH350H heads, when I'm ready to throw more money at my motor.

 

[bucket]

The 416 heads are decent head for their cost (free) and have the smaller chambers.

I have personally ran a set of ported 305 heads (450 casting) on a 350 with a very mild cam. It was a TPI motor. I thought it was a combo that worked very well for the application, and wouldn't be afraid to do it again. I still have the heads, as I will use them again on something. Maybe with a Crossfire injection setup... I know folks will call me stupid for it, but I know it will make a strong low-mid range motor.

I also know of a professional engine builder that swears by 305 heads on a street motor, of course, he ports the living snot out of them.

 

[rollinon35s]

Not positive but i am guessing the 416 heads have the 64 cc chamber which is good, I had a set built for my truck originally but unfortunately they were the 58 cc heads. The 58cc heads definitely boosted the compression but in my application (350 bored .030 with 4 relief flat tops) BUT even with the 1.94/1.60 valves I had installed it did have lots of torque due to the high compression but the power faded really quickly and the extreme compression caused lots of running issues with pump gas. The only way the truck would run decent was by adding race fuel to the mix. My brother is running a set of 305 heads with the 64cc chamber that he ported to hell on his 350 with dish pistons and that truck runs like a bat outta hell from idle to 6000 rpm, so every application is different. If you have them already, and have the ability to port them out well, I say run them. If they don't give you all you hope for you can always upgrade later when the funds are there. I believe they will definitely be an improvement from the seat of your pants take off feeling over the stock 350 heads. just my opinion though. good luck with whatever you decide. Lots of guys on here with more knowledge than me to help, just sharing my own experiences

 

[yevgenievich]

I had a truck with 305 headed 350. It ran strong up to about 4.5 - 5k rpm and then it was out. I picked a cam that would match and it made for a nice street motor. It did like premium pump fuel and had some tunung issues(i sorted most of it out by the time it got sold)

 

[Mohawkman]

Thanks so much for the info guys. I think I'm going to give it a try. Got to do a compression test and make sure the heads are straight before I know for sure. But I took a quick look at them this morning and it looks like they may have put new valves in when they did the springs. I'll try to snap a couple pictures for you guys tonight. Glad I finally decided to join this forum. Been trying to find this info for a truck application for a couple months now .

 

[MikeB]

I agree that the 416 heads will work OK with dished 350 pistons. (I think the chambers vary from around 55-58cc chamber volume.) And the cam you mention should make more power than a stock 350 cam. I personally think this cam would be better: Comp 12-305-2, 203/212, .429"/.438". http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=69&sb=2

Don't forget to address the basics first -- dual exhaust, performance ignition timing curve and optimal jetting.

 

[Mohawkman]

I agree that the 416 heads will work OK with dished 350 pistons. (I think the chambers vary from around 55-58cc chamber volume.) And the cam you mention should make more power than a stock 350 cam. I personally think this cam would be better: Comp 12-305-2, 203/212, .429"/.438". http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=69&sb=2

Don't forget to address the basics first -- dual exhaust, performance ignition timing curve and optimal jetting.

Thanks for the info. I'm just looking to use what I already have but here some pics of the 416 heads