Will accommodate center bolt valve covers with minor modifications. Features ductile iron seats on exhaust ports only for use with unleaded gas. Machine work must be done to accommodate guideplates. Springs are set up to run hydraulic flat tappet cam only. Coolant temperature sensor threaded hole is 3/8 in. NPT.
Summit Racing® Cast Iron Cylinder Heads for Small Chevy
Think you have to scour the local bone yards to find a decent set of GM's old double hump or fuelie cylinder head castings? Not true. In fact, we've brought back classic Chevy performance in a big way with these ready-to-run heads for small block Chevy. Our versions of the popular GM cylinder heads offer great performance for less than it would cost to rebuild an old set of double hump castings.
Thank you for your question. The Summit 152123 Cast Iron Cylinder Heads for Small Chevy utilize a 3/8 in. NPT threaded port for the coolant temperature sensor.
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If you are referring to where the the temp sending unit goes into the head for your temp gauge
I believe it is 5/8 s smaller then a standard size
I just ordered and adapter kit came with 5 or so fittings to pick from no problems
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Q:
Hi. I have a 1975 Chevy G20 camper van with the original 165hp LS9 350 (the 70's LS9) with stock heads (GM #14034811). I'm trying to decide between this Summit head and the Chevy Performance Vortec head (12558060). I know the Vortec is hard to beat, but I won’t be racing or towing. I almost always stay out of the Thermoquad secondaries and drive smoothly for high MPG (low highway speeds, too). I'd be happy with 20 more HP over my stock motor, just to help maintain speed on steep mountain highways. Otherwise, it's all about improving MPG’s, keeping my highway RPM’s low, and having nice starting and idling, with no warm-up needed before driving. I am now leaning towards these Summit heads over the Vortecs because they have a heat passage for a nicer-running cold engine, and I have a heat riser choke as well (so, less mods needed). Do these heads make more sense for me? What compression should I be targeting? These Summit heads are 72cc chamber, the Vortecs are 64cc, my stock head chamber volume can’t be found anywhere. Are there flow numbers available for the Summit heads at .05” - .5” of lift? Will the style of stock piston I have (GM #3991488, see photos) match one head much better than the other, or is it not much of a factor for a daily driver? Is quench an issue with either head? My stock piston # matches to a Silv-O-Lite 1476H or 1470. I’ll be replacing the stock cam with a suitable high-MPG cam from Summit, Crane, Comp, or Lunati. I’ll also replace the stock intake manifold with a Edelbrock Performer Vortec, if I go with that head. Intake suggestions, if I use go with the Summit heads? My motor has GM H.E.I., EVAP, and AIR, but no EGR. My trans is a TH350 with a 3.08 rear end. I have AC and power steering. FYI - I am paying a mechanic to do this work, so budget is a concern. I don’t want to tear apart the block, swap to an OD trans, etc. Thanks for any and all advice!
The heads are good I use them for a stock replacement my truck runs really well I use the summit roller tip rockers 1.6 for little big a lift on a cam so I don't think you'll have a problem I have an 86 Blazer stock 350 I also have the summit Aluminum Intake on it so far so good
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As far as these heads are concerned, they're a huge improvement from the stock heads. I can fire my 86 C10 up and drive pretty much immediately. The performance is greatly improved and I'm even getting close to 2.5-3.0 mpg more than before. You will notice an even better improvement if you also upgrade to a set of full rollers while they're doing the work for you. As far as the vortec questions, these particular heads are for a non-vortec motor. But I believe they have a vortec version of these heads with the same specs. You can also look at getting a top end kit. They usually come with everything you listed to be changed out. I hope this helped.
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Ok, in my opinion, the reason I used the old style head on the older motor there were less overall issues. The easiest being 72cc chambers. A non-issue with compression and today's cheap gas. You have a heavy vehicle with street use. The vortex heads have a little more horsepower problems, small chambers, new intake manifold and also the bigger time consuming issue was valve covers, grommets that fit the bigger holes in the valve covers and plumbing your pvc back together. The old style heads were my choice having done the vortex head conversion on a motor before this one.
Thanks.
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Summit heads are great. a good point about them is the motor u have will have smaller valves so just bolting summit heads on you will notice more pep also these heads have a vortec style dome for fast burn they work great
I use them on a 355 motor with lunati cam and Tunnel ram and love them and have them on stock 350 my tow rig and love them for the money I would say best value and all around great
I think you would be happy with them and yes just bolt them on it all will fit with no hitting of parts and there great you can even hear the difference when starting up good luck hope this helps
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These heads are better for you than vortec. They are better than the stock heads for your situation. I have almost the same set-up as you and they work great. Lots of torque.
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Q:
What type of rocker arms are needed, for example. Do I need to get self aligning rocker arms, get guide plates. Or are these heads like some of the old sbc heads that the slots in the head align the rocker arms? Thanks.
Thank you for your question. The Summit 152123 cast iron cylinder head can use the regular rocker arms if used with the regular valve covers. If you would like to use the center bolt valve covers, use narrow rocker arm.
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I’m no expert, and quite possibly should not be attempting to answer your question. Because of some extenuating circumstances on your build that I am totally unaware of. However on my build I could see no reason for guide plates or self aligning rocker arms with these heads. I used off the shelf roller rockers and roller lifters. But need need specific length push rods. But on the flip I’m building a low end torque truck motor not hi end rev. race car motor. Best bet that I would suggest would be to do the valve train geometry and go from there.
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I used stamped long slot roller tipped rockers. The heads come with screw in studs, and guideplates aren't needed as the heads have the aligning slots you are talking about. If you do buy these heads, drill and tap the temperature sensor hole to 1/2 inch pipe, or you'll never find a sender to fit the 3/8 pipe hole already in the heads. Other then that, the are a great head for the money.
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My machine shop said do not use guide plates because the openings are right sized for push rods just like the old ones. If guide plates are installed it would be very difficult to line up the openings in the head to the guides.
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The Heads are the same as Stock Gen.1. If You want to use Guide Plates, You will have to mill .125" off rocker stud surface and open up the stock pushrod holes. Any Gen. 1 rocker arm will work, Check Alignment and pushrod length.Also stud length could be an issue with Roller Rockers.
WOW GOOD HEADS!!! CHEAP!!! WHEN I CRACKED ONE OF MY CAMEL BACK HEADS I THOUGHT THAT IT WAS THE END OF THE WORLD. I SUPRISED TO SEE SUMMIT HAS THESE AWSOME NEW HEADS, FULLY ASSEMBLED AND READY TO GO. I RECOMMEND TO CLEAR COAT THEM. BE ADVISED THAT THEY COME WITH THE SCREW IN STUDS, I DID NOT KNOW THAT AND I BOUGHT SCREW IN STUDS THAT I DID NOT NEED. GREAT BANG FOR THE BUCK! MADE IN THE USA.
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Quality
best bang for the buck!
5/1/2015
Summit Racing Verified Purchase
SUM-152123
heads were cheaper than rebuilding my old ones, so i bought them with average expectations. first pass was 12.49 at 108mph on radials easing it off the line! 3200lb car with 373 gears 650 carb 10 inch converter and full exhaust!
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good value for the price
5/1/2014
Summit Racing Verified Purchase
SUM-152123
heads worked really well in my boat application. machinist was impressed with the quality of the heads- (this guy builds sprint car engines). was cheaper buying new than reconditioning old heads. all the external accessories bolted up without issue
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Great set of heads
6/2/2015
Summit Racing Verified Purchase
SUM-152123
I put these heads on a SBC 355 and I was very impressed. I do not like aluminum heads, and Summit had these iron heads priced just right. I'm not going to name the maker of these heads, but it starts with a "D" and ends with a "T". I was very suprised and happy to know they made them. Only disapointment is they come with 72cc chamber. Wish they came with a 69cc or even a 67cc. Had to put a thin shim gasket to get the compression i wanted. Another is they have "Summit" milled all over the front and back of the heads. I just grinded that off and repainted.
Summit Racing Verified Purchase
