[67Lemons]

I’m building a 455 with 7K3 heads, TRW flat tops and RA manifolds for my ‘72. The car is a cruiser with a 3.23 rear and M20. I know the pistons aren’t ideal, according to Butler’s compression calculator I’ll barely be at 9.0:1, I’m hoping the shop can shave a little off the heads to bump it up. I’m not a position to replace the pistons since it’s a simple refresh to an already built short block so I’m working with what I have.

I sent a cam recommendation into Butler and they suggested their 8024SP which seems like a really popular grind for them but I’ve also heard great things about the Stump Puller which has a little more lift from the specs I’ve seen. So I’m at a crossroads at this point and need to order a cam soon so I can get this build done before spring.

Edit- Butler grind (HR) (Std Firing Order/ Std Journals) 282/288, 230/236, .510/.521, 112 LS with 1.5 ratio rockers
SD Stump Puller 230/236 dur @ .050" lift .590"/.592" lift with 1.52 ratio rockers 112 lobe sep

Any thoughts either way from the fine folks at PY?

[tom s]

IMO get the more lift.Tom

[AG]

If you plan on upgrading to an Ali head later on I would go with the higher lift cam. The 7K3 heads will top out on flow around 0.450" lift so the extra lift will not get you anything. Also, you will need a longer valve and have to cut down the valve guides and maybe spring pockets on the 7K3 heads to accommodate the 0.592" lift. If you plan on staying with the 7K3 heads you can go with the lower lift cam and it will be easier.

[steve25]

You did not say what your Bore size, but I calculated your compression at both a standard bore and .030” over .

In these results I assumed a deck clearance of .020” and a head gasket volume of 9.4 CCs as in a Fel Pro 1016 gasket, and a chamber volume of 96 CCs a long with 1.5 CCs for top ring land volume.

At a 4.150” bore 8.9 to 1.

At 4.180” 8.93 to 1.

If you mill the heads .030” which is very safe and will still allow the Intake to bolt up with out an issue, here is what you have .
4.150” 9.3 to 1.

4.180”. 9.35 to 1.
With your rear gears I would run the Butler cam as with stock heads there no sence to stuffing in more lift then that.

[scott70]

If a head has max flow at .400 lift is it detrimental to run a cam with.600 lift?

[steve25]

No it’s not, but it does add more friction due to the added spring pressure which can negate any added power that might be had and with the added lift of the other cam I would not chance running stock well used valves .

7K3
Stock flow numbers@28”
Intake —————exh
.050”——39..5
.100”——75.8—-50.2
.200”——135.3——95
.300”——177.5——128
.400”——198.8——148.4
.450”——203.7——152.9
.500”——206——161
.550”——208.4——163
.600”——209.8—-166.4
.650”——————-168.2
.retest with 2” tube
.650”——————————-184.6
Running .500” lift should get you to 415 hp easy.

[Steve C.]

Adding this here for interest only, and note this statement... "if the port has been modified to support flow in this lift region".

Material published by David Vizard:

VALVE LIFT.
"A 2-valve cylinder head typically continues to flow more air up to lift values equal to as much as 0.35-0.4 times the valve diameter. The reason for this is that there is a flow pattern transition period that takes place at a lift value of about 0.25 of the valve's diameter. When this point is passed, if the port has been modified to support flow in this lift region, the valve efficiency actually starts to increase. This is the reason why a 2-valve engine responds to high lift." "If you want to build a street motor with the most power without a sacrifice of idle and low speed qualities, then lift is the most important factor to maximize, not duration. The best street cams are those that seek to maximize lift while only adding a minimal amount of duration."

Bottom line, the engine wants all the lift it can and thrives on it so run as much as mechanically achievable or prohibitive to you because of cost and/or budjet limitations (such as in a purchase for solid roller cam, longer valves to increase installed height, stronger springs, etc.). Obviously if it's a street application or race application will have a bearing on the situation, most here would be hesitant to run 0.700 lift on the street.



.

[PAUL K]

Butler cam without a doubt

[KEN CROCIE]

Butler! The SD cam will make a little more power on the dyno, using headers, but when using manifolds and an exhaust system, you won't see a difference. AND you won't be as hard on the valve train.

[srmmmm]

Originally Posted by steve25

If you mill the heads .030” which is very safe and will still allow the Intake to bolt up with out an issue, here is what you have .
4.150” 9.3 to 1.

At what point does he have to start worrying about valve to piston clearance?