using 273 heads on a 360

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crabillac

crabillac

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I have a set of 64.5 cc closed port heads taken from a 66' 273. They were reworked, and the valves were opened up to 2.02 for some reason or another. I want to use them on a 1975 360 with 9:1 pistons, and a larger then RV cam. Will these heads work with my application, or should I use the original generic heads, and trick them out some way or another? Also what is the difference between the way that a closed port, and open port head functions?
 
Well, they will bolt on fine, but that's about it. The 273 heads have a small port volume which will support 250-300 hp at best. And, although the larger valves may help low lift flow, the small port volume will ultimately be the restriction. 2.02 valves are not a popular mod on 273 heads because there is very little if any gain, especially if the bowls are not opened up. Bigger exhaust valves would make more sense, but even then, the gains would be marginal without significant porting.

If you want a low RPM high compression torque motor for a 4x4, this might be worth considering. But generally it would be a step backwards performance wise.

9:1 360 pistons? Really? What are they? Compression height? Dish volume? Who made them? Most stock 360's were mid 8's compression wise.
 
The pistons have not yet been purchased. I am awaiting measurements to see whether to order stock, or go .030, or .040 over. The reason that I put down "9:1 pistons" was as an reference to the compression that I am going for. I am considering using Speed-Pro H405 CP plus perfect Circle/Hastings moly rings 2M139. The compression distance is 1.637 and the heads will be no larger then 65 cc to pump compression up to approx. 8:94:1. My main question was answered. My main concern was about the difference in port size/match-up, and how that would affect the build. Thank you for your reply!
 
Why??..the ports on 318 heads are dinky i can imagine how small they are on 273's..get yourself some 340/360 heads with a much better port design/size..
 
Ummmmmmmmmmmmmmmmm, theres s et @ .030 in the 4sale section now.

The KB-107's will give you a 9.8-1 ratio with normal open chambered 340/360 heads with a .039 gasket. Just a FYI thing. Careful on the Fed-Mougal pistons. They do give the compression height. Calc. this into the math problem and see for sure where you stand. IIRC, there a stock replacement piston. The CP116H is what you should be looking at. It's compression height is slightly less than the KB-107's and rated IIRC @ 9.5-1 with 340/360 open chambered heads.

I would sell the 273 heads and roll the money over into stock 360 heads which are capable of 380+ HP. (With 2.02's)

The smaller head port will not be a big issue. The engine is just breathing through a straw instead of a nice feeding/breating pipe.

stroked 340 said:
Why??..the ports on 318 heads are dinky i can imagine how small they are on 273's..get yourself some 340/360 heads with a much better port design/size..
Click to expand...

Same size port and valves set up. It's a RPM/power limiting item on the bigger engines. They'll make great torque up to 3000 rpm and then just die right off.
 
I totally agree. I bought the 273 heads by mistake off of e-bay because I thought that I would save money on machining. but once I received them... I found that they were actually heads from a 273. I was under the impression that they were newer/different heads then what I actually purchased. I was just trying to some how remedy my foolish error. Will the heads work on a 318 out of a 68 B Body? IF NOT... Is anyone out there looking for some heads for a 273? Let me know. I am in the Chicago/Milwaukee area.
 
The further away form the intake valve the "Choke or csa is, the less power it will make.
Therefore a 2.02 wouldn't be a good choice intake valve for 273/318........

Stock 360(1.88 intake valve) head would, on a 273, out run the 273 with the 2.02. JMO

A larger valve is a good idea....... until it creates a choke in the port.......then your only going back wards!
 
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