I have a 327. Block # 18j29517a, t0617hn, f 15-8. Heads #291. Weiand stealth intake with Holley 3310 v/c, 72 jets with rear #21 plate. Fresh from machine shop and dyno. Max 330.5 ft and 336.5 HP at 5700. They put comp cam 12-601-4 in it. I have a turd I think. What do I do. .030 over dome pistons.
More details needed , there ate other factors , Whats the compression? That Little 327 needs to be spinning @ least 6,500 plus, to make Hp. Cam kinda small What size vale's & cc Whats spec's on Vehicle There timing , stick or auto
11.1. Small valves. 1938 Plymouth coupe with turbo 400, 2,800 stall 4.11 with 29in tire. About 2,700 lbs.
Heads cfm needed , ported & 2:02 & good tunning , @ least 91 oct Back in 86 1940 ply 2:02 ported 327 10:5:1 ,030 Torqer 750 vac Crane .488 in & ext 6,700 400 2,800 28 tall tire 3:73 8.10 1/8 @ 91 mph On a 125 of spray low 7:80s
If you were looking for 350 horsepower, you are only 14 away. Sounds like you should be able to pick up that with a better cam and a little tuning.
As mentioned without knowing the car, car weight, transmission/converter stall, gear ratio, and rear tire size as well as intended use one cannot give the best advice. That said, that cam is probably not a good choice for that engine in a street driven car. It has 235 int./249 exh. duration @.050" lift and only 107 deg. lobe separation with .489"/.467" lift. For a Hyd. flat tappet something with 224-230 @ .050" duration and 110 deg. LSA might be better.
Your numbers are interesting. The L-79 was factory rated at 350 horsepower with a smaller camshaft and smaller carburetor. Your cylinder heads are very close to the L-79’s too. Hmmm? Are you sure you have a true 11 to 1 compression ratio. I believe the L-79 was 11.25 to 1. Has someone done some “porting” that might have done more harm than good?
I was always under the impression that those "thumper" cams were more about making a tough sounding idle than making horsepower. You probably would have been better off with the factory L79 camshaft
I'd suggest better heads and less cam. Less cam for sure,even if you keep your heads. That Comp Mother Thumper has 85 degrees of overlap and is not great for bottom/mid power in a 327. I'd say something in the range of a Summit 1202 (it's a 4/7 swap cam but that doesn't matter) would be a much better choice. That range of cams from Summit have been performing very well.
Pick up the phone and call Chris @ Bullet Cams (662)893-5670. They custom make every camshaft exactly to the application, we have been using them for 20+ years, just finished a Pontiac 389 that we had them do a custom hydraulic roller for, runs perfect. Bullet Cams DO NOT try and outsmart yourself picking cams from the internet sites.
The Comp Thumper cam is hurting your performance, and maybe heads also, as those were decent heads back in the 60's, but almost any good aluminum heads give huge increase in performance and flow today. The duration and LSA makes the cam sound good, but lift is puny. Most likely they use the lower lift to ensure the cam works with any heads and piston. A higher lift cam will help, as will an LSA of around 109 too. You'll need more head work to have those heads work with a cam that's around .500" lift or more, and they need better springs, spring pockets cut deeper, and then you'll still have maybe 160-170cc port runners. Even later Vortec, or any aluminum heads will increase your dyno readings greatly. If you also change the camshaft too! What chamber size are your 291 heads to get 11:1 CR? Sounds like you've either got tiny chambers, or a domed piston?
Machine shop is pulling your leg on the compression ratio. The only way that piston is 11.2 is with everything at or near minimum blueprint spec. You said no decking, block or heads.....so that's barely a 10.5:1 compression ratio if you are using a typical composition head gasket that is about .040" thick. Using a steel shim head gasket would push that up to about 10.7:1 Otherwise with a 64cc head you need to deck block and mill head to make that piston be 11.2:1.
Basic calculation: Bore: (diameter) 4.030" Stroke: 3.25" Cylinder Head Volume: 64 cc Effective Dome Volume: -5.3 cc Deck Clearance: .026" Compressed Gasket Thickness: .040" Number of Cylinders: 8 Compression Ratio : 10.35 : 1 Zero deck would bring it up to 11.1:1 So ya. Someone's blow'n smoke up........well you know
Interesting. I just dug out the dyno sheets on the L79 from my '67 Corvette that was "professionally built" in 2008. It was basically a stock build with lower compression pistons (so I could run premium unleaded) and a Comp Cams 262H. It also pulled 336.5 hp, but at 5900 rpm. Given my purpose at the time, I was happy with that number. Given today's standards, the car is a slug.
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