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Cyclinder head question?

Mudbug1979

Mudbug1979

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OK, I have a 350 that's been bored out .40 and it's the old style outside bolt (valve cover) head. I've installed TBI and been running it for about 2 years now with no problems, about a year ago I installed a new cam Made for a TBI motor becuase the cam that was in there was causing me a vaccume issue with the FI. I have a TBI motor at home that has a knock in the bottom end, but the heads are in decent shape. QUESTION, Would it be beneficial for me to remove those heads, have them gone through and install them on the older style motor? It's not a built motor and that's not what I want, but I would like a little better performance and from what I've read this will supposedly help me. I have a set of shorty headers, but I want a good set like Thorley's or Elites, but I want to do this all at the same time. Thanks.
 
hell no. TBI heads suck. I'd venture to say that most if not all 350 heads from back in the day are better than stock TBI heads.
 
id have to strongly disagree with that statment, the crappy head designation is in regard to 305 heads because they use smaller 1.84 / 1.5 valves instead of the 350's 1.94 / 1.50 valves and tend to have smaller intake runner volume. however these faults are only evident when youre trying to make a race motor, which you said youre not.

my two cents, depending on the year of your TBI heads, they will have smaller combustion chambers, (58cc i think) which will raise your compression, so youll have to crunch some numbers to make sure youre not going to have detonation problems. but older engines have normally 8:1 - 8.75:1 compression so with the 58cc heads and the .40 overbore, you might be flirting with 9.5:1 compression depending on what thickness of gasket you are running.

so basically, so long as you dont run into detonation, youre gonna have a set of heads that make great low end power, possibly better gas mileage from increased compression and efficiency, and with the centerbolt valve covers youll have fewer oil leaks to worry about. youll just have a the "drinking through a straw" problem at higher rpms. for a truck, id say the swap would be worth it.
 
i didnt know if you knew the numbers to crunch on this and i had some spare time so i decided to play with it. i made a few assumptions but other than that it should be accurate. youve got a .040 over 350 with a 3.48in stroke right? i put an "*" next to things i assumed but am not 100% sure of.

Cylender volume - 44.61 cubic inches - 731.026 cc
combustion chamber* - 58cc
gasket volume with a .045 in thick gasket - 9.45293 cc
gasket volume with a .015 in thick gasket - 3.15098 cc
Piston Dish* - 18cc

total combustion chamber size - 76 cc

so with a .045 in gasket youd have a 9.55472:1 compression

with a .015in gasket youd have a 10.2358:1 compression.

although these compressions are actually a bit high, because i left out the volume above the piston when its "in the hole" at TDC. but i have no idea what value that is for your engine, to hazard a guess of .040 in in the hole would give about a volume of 8.4 cc's, and change the compressions to..

8.78906:1 and 9.34972:1 respectivley.
 
K 5 screamer makes a good point. I will add think and shop hard 'cause depending on what they need rebuilding heads adds up quick, often your ahead w/ new aftermarket heads or oem vortecs ( different intake though ).
 
scoggin-dickey will sell you a set of vortec heads drilled for the old style intake bolt pattern
 
Can you post a link to those vortec heads drilled for older intake? Not saying they dont have them. But i would like to see how they work. I dont see how an older intake can be made to bolt up to them properly. Because the intake runners on vortec are bigger and taller than the older heads and the manifold does not match up to them. Also Vortec only has 8 intake man bolt holes old style has 16.

Re: The question about swapping to TBI heads for more performance. I dont think so. Al ltho i do think TBI heads are a great truck head. They run out of breath around 4500 RPM. So does the intake manifold. The only gains you will see from the swap will be better low end torque and prolly better gas mileage.
If you want a little better performance.............
Beings you are runnng a cam I would keep your old style heads. Get a better intake, Headers, adjustable fuel pressure regulator, and a new chip programed for the better flow you have.
TBI heads can be made to perform better but it takes some porting to make them flow. They have large 185 CC intake runners. But They have a big ramp in the valve pocket that restricts the flow. This ramp is GMs early attempt at a swirl port head. It causes the FA mixture to mix better so it combusts better at low rpm.. The ramp needs to be cut down reshaped. to make the heads flow. So unless you can do the porting yourself. It really aint worth paying someone to port them when you can get better heads for the same price.
 
BadBob said:
scoggin-dickey will sell you a set of vortec heads drilled for the old style intake bolt pattern
Click to expand...

Scoggin Dickey will sell you alot of useless crap if you punch the right part number into their website. the Vortec head intake ports WILL NOT line up with an older model intake properly. the runners are raised .100". bolting on an older style intake will create a wall which the intake charge will hit, and then have to flow around. this action would negate any possible advantages to running Vortec heads, if not hurting the performance even more than the current heads.
 
Petersons 4wheel had a writeup where they took a crate 350ci 350hp and bumped it up to 39?hp. The first thing they did was replace the stock heads with TBI heads. They referred to them as early vortec heads, 1986-1995 with the swirlport design. Then they added a cam and got close to 400hp. Now this was on a carbed motor, so its not exactly the same setup as yours, but I would give them a try.:thumb: And in fact I did try this on my carbed 400sb with a rv cam. :D Now these heads may suck for the high RPM crowd, but I love em since I seldom get past 3-4000.
 
4500rpm

That's fine with me, I didn't build this motor and it has worked fine for the last 2.5 years and I haven't turned it much over 4500rpm. I have no plans of building a motor anytime soon so this one has to last me for awhile and that's why ever change has to be beneficial and worth the time/money. The guy who is going to freshen them up said it would do it for less than $200.00 and I don't have dime in the heads as they are, I didn't think that was too bad of a deal. Would it be beneficial to move up to an Edelbrock TBI manifold or is anything else better than that? I knew you guys would know and that's why CK5 is the best site on the net.
Thanks to all, Jeremy.
 
if you dont mind spending the money the edelbrock TBI manifold would offer up a few ponies, but i wouldnt imagine it would be seat of the pants noticeable with the stock cam, throttle body, and heads which greatly restrict the airflow. Personally id save my money and spend it somewhere else.
 
K5dreamer said:
id have to strongly disagree with that statment, the crappy head designation is in regard to 305 heads because they use smaller 1.84 / 1.5 valves instead of the 350's 1.94 / 1.50 valves and tend to have smaller intake runner volume. however these faults are only evident when youre trying to make a race motor, which you said youre not.
Click to expand...

No, the problem is that swirl is induced by a huge ramp just in front of the intake valve. It was an effective (but inhibitive) attempt to get better combustion.

The crappy performance has nothing to do with the 305/350 issue, it's that. Small valves won't help, but they didn't do small valves on the 350.

Besides that, 350 heads for TBI our vintage never exceeded what, 8.5:1 CR, and were nowhere near 58CC. 305's were up around 9.2:1 since the inception of ESC with their 58CC chambers. They HAD to run ESC because the crappy heads combined with the high compression could result in engine destruction in short order. The 350's didn't (until TBI) use/need this because the compression was never high enough to worry about.

I'd like to see the article in Petersons, there is (in this regard) no such thing as early Vortec, they either are or they aren't, short of the 4.3L "Vortec" badged motors that came out much earlier. Did they swap JUST heads then dyno, or did they do the typical cam/heads/exhaust/tuneup at the same time then claim that they all made power?

If you don't need high end, then yes, the heads are probably fine, and are probably more effective at low end than earlier heads. But just like under or overcamming a motor, IF you want the power at some point, you won't have it.

http://www.tbichips.com/truckmods.htm I like #2. :)
 
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