I joined the H.A.M.B. a day or so ago, so I just put my intro on that forum. I've got a question about Chevy cylinder heads. Here's the story. My '52 Chevy pickup has a '68 327 from a Caprice/Impala/Biscayne. I believe it was the low-hp model originally. It had the 1.72/1.50 "single hump" heads when I got the motor. Long story short, I scored a set of 2.02 heads for it, but they were unusable due to cracks, bad seats, etc. I had the stock heads rebuilt and used those instead. Now, I'm having an intermittent miss that I believe is a failing valve spring or burnt valve. While I've got the heads off, i'm wondering what to do. Do these heads have any performance potential, or should I just retire them? I've always thought that this motor doesn't breath well. BTW, I've got TRW 10:1 pistons, .030 over, Crane "Blueprint" cam, Edelbrock 600, factory 300-hp intake and ram's horn exhaust manifolds. I really can't find much info on these heads. Any input would be greatly appreciated.
If the heads are still on the car, do a compression check, check for full rocker arm travel at each valve, and look for broken valve springs. Also listen to the exhaust, a burned valve can result in a "puff" sound every time that cylinder fires. And do some thorough checking into the ignition and carb as some problems show themselves in strange ways... anyways, you could get a bit better breathing with some run of the mill 70s 1.94 smog heads, with flat top pistons they should give enogh compression to run ok, especially if you do a bit of mild porting work to clean up the bowls. Or look around for a nice used set of fuelie heads, there was a post a couple months ago about how nice they work and how easy they are to find already done ready to go...not that I've ever found any that way....
I had a flat cam lobe on my 327 and it still didn't miss, well at least I didn't notce it much. My guess it the miss is related to the carburetor. You would have noticed teh burnt valve when you took them off, and hopefully when they were rebuilt new valves were installed. I had trouble with my 71 mustang because the stock 351 Cleveland 2B heads and valve train could not keep up with the cam, dominator intake and double pump carb.
Or the Vortec heads are still in the $500 range and then he would have to upgrade the intake for the newer bolts, which is not all bad.
Jonnyquest I'll share some info. I have a 68 327 as well. I had the same issue too. I'm no SBC guru but here it is. I Couldn't get a steady vacuum, rough idle, could not set timing right. It took about two months to figure out that it was the heads. I had a loose valve springs, nicks on the rods, and valves net seating right. Took them to a machine shop in Reseda Ca. and found out that not all heads are created equally. Meaning there were heads with smaller ports for 2 barrel apps and bigger ones for the 4 barrel apps. Measure your cylinder head size, I think 2" is the Hi-po and the 1 and something inch is the economy. The machinist also told me, What also made sense, if you build up an engine that it needs to breath and that you'll have to swap parts out to achieve the performance. The bigger ram horns (2"), using a hi-po cam and have the heads internals compensate the cam and such. Hopefully somebody else can say more as I'm always learning and love to hear more. Oh also, if you take the heads off, everyhing should be lined up, shouldn't look like an equalizer.
I've already pretty much eliminated electrical and carb issues. I set the valves running and everything appeared to be opening and fully closing, and the push rods are very straight. It's timed right, as well. Everything else is brand new (carb, dizzy, etc.) I don't have the heads off yet. I still need to do a compression check, b/c I think one cylinder on the right bank is the culprit. Are 305 heads any good? I know they're plentiful and dirt cheap.
I had a set of 305 heads on my coupe. (67 327) They worked pretty good for dirt cheap. I changed a bunch of stuff all at once, including adding 186 heads. So I don't know how much of the difference was just the heads. The 186's had a fair amount of port work, good valves and springs, and everything was okey dokey. Car ran way better and pulled harder. Like I said though, I changed cams, gears, carbs, and tranny all at the same time. I was pretty happy with the car at that point, but wanted more. Lux, Racefab and the HAMB convinced me that to go fast, aftermarket heads were the way to go. I went from the 186's to Dart Iron Eagles, and added an MSD distributer, and dropped 8 tenths off my quarter time. That's with zero port or polishing on the Darts. The car pulls way better through the mid range, and idles better. The idle is likely do to the better distributer. A grand is a bunch of money to me, but it was way worth it in performance. From the description of your motor, it looks like the heads and maybe the exhaust are the "weak links" to power. Disclaimer: I ain't no expert type guy. I made the changes based on the advice I got from guys in the know. But my time slips and seat of my pants tell me they were right.
The later 305's had crappy valve guides, but that is a cheap fix. I am sure they could work for you. I think some aftermarket group actually sells them reworked in Summit.
do you know what piston you have .. the actual part number,....... was the block decked at all when it was redone. A 1.94 /1.5 valve head would work great for your application. I could help you find a set for under 500.00 that would be set up , ready to go performance wise.......If you can afford to spend more I would be looking at aftermarket heads.....skip the vortecs ands just start looking at the DART or AFR'S etc. if you do go aftermarket, make sure and have a machinist check them out before you bolt them on, valve to guide clearance...and valve seating especially. pick Buzzards brain a little...he has been down this road recently. let me know if I can help you Fred
if ya go with the darts or afr's or any aftermarket head.....go small on the runner cc if your driving it on the street with a small cam...( i mean don't go straight for a 220 runner just because it sounds cooler) ...a customers 406 made just under 500 hp with a small pair of edelbrock performer rpm heads.....i think they were 170 ish on the runners......too much head on a motor can be just as bad as too much cam or carb .....well ...almost.....brandon
hope it works this time http://cgi.ebay.com/ebaymotors/SBC-CHEVY-CYLINDER-HEADS-195-CC-ALUMINUM_W0QQcmdZViewItemQQcategoryZ33617QQihZ016QQitemZ260057174515
Does anyone know what runner size the 1.72/150 heads have? I'll use the stock heads if a simple valve job and new springs is not a total waste of money.
if they are the single hump style, they are more than likely the 3917290 casting...these were used on 327/307's in 68. they are a low performance head, but they will work. They tend to start giving up at 3500 RPM and above...this is why people notice a "seat in the pants" difference when they bolt on new heads. If finances dictate that you have to use them..use them...have a valve grind done and install new springs /retainers /keepers. if you have someone you trust to do the valve grind and set the springs up, let me know what the cam specs are on that cam and I will send you a set of springs/keepers/retainers for it....... A present from the HAMB I would stay away from the no name aluminum heads myself, there is a flood of off shore castings all of a sudden and everybody seems to have their own head now. all kinds of new names for what seems like incredible prices. Fred
Chevy High Performance flow tested a pair of 462's with 1.94/1.5 valves and 156cc runners. Yours should be the same. Click on "smaller than 180cc", at the bottom. http://www.chevyhiperformance.com/techarticles/41598_cylinder_head_flow_bench_database/
Hi. If you haven't decided what to do yet here are a couple suggestions. Go to mortec.com and find the casting number on your heads from the web site. Then you will know what you have. Generally speaking the 1.72 valve heads were used for low horse power motors. But they did have a small chamber head used on 283 high performance motors. In my opinion 2.02 valve heads are not good for street use, stick with 1.94. With any head you should get a smooth motor if the valves were done properly. Be careful there are a lot of hackers doing valve jobs. By a blueprint cam do you mean the 300hp or 350hp cam? Either case you want a 1.94 head, stock or aftermarket. The 300 should idle very smooth, the 350 will have a bit of a roll. I have used both of these Crane cams in the exact setup you have with 1.94 stock heads, both resulted in nice running motors. Hope this helps, John
I'd recommend a cylinder leak-down test rather than a compression test, I think you can find out more that way. If you have 15% leakage in seven holes and 30% in the remaining hole you know where to go....alot of times a regular static compression test may be misleading. You can repeat a leak test "wet" (use a little oil) also to see if anything is going past the rings.
I've got the 300-hp Crane Blueprint cam. In the last week, I had a compression check run on the motor. Overall, I was getting 85-90 lbs "dry" and 105-110 lbs "wet" throughout all cylinders. This motor sat for quite some time while I was in college, etc., so its pretty obvious it needs rings badly. I'm sure that's probably throwing things out of whack, as well. Over the holidays, I'll probably just yank the motor and put in new rings. I think I'll try to get ahold of some 1.94's (even if they're 70s smogger heads) b/c its got to be a huge improvement over what I've got. I think if I start messing with the old heads, I'll just end up throwing money at something that isn't going to improve much no matter what I do.
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