302s on 72 340

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rigger3006 said:
heads are off, 302s have been mildly worked, considering doing a bit more, 750 sllayer will be the carb, thinking 040 gaskets are in my budget which is basically nil right now. and by norm i mean all the "norm" advice given on this forum. once again, this is NOT a
performance build
Click to expand...

Then go with the 600 cfm Slayer, a 750 is way too much for NOT a performance build. J.Rob
 
ya,guy at engine shop tried to talk me into buying a set of eq's or similar, 750 is carb she'll run for now, not buying anything new, if its an issue i may swap my 670 avenger onto motor. just measured and pistons are 055 in the hole
 
So you're at around 9.3-9.4 SCR with a .028" head gasket.... not too awfully high. I think I would put on the 670; the 750 won't be well used IMO.
 
rigger3006 said:
once again, this is NOT a
performance build
Click to expand...
That's fine. I'd figure running terribly on premium is not a goal though.

rigger3006 said:
ya,guy at engine shop tried to talk me into buying a set of eq's or similar, 750 is carb she'll run for now, not buying anything new, if its an issue i may swap my 670 avenger onto motor. just measured and pistons are 055 in the hole
Click to expand...
Should be fine. That sounds about normal for the stockers.

The EQs outflow the Magnums and the Magnums matching the 340/360s with tight chambers is a positive.

RAMM said:
Dude you coulda had a set of EQ's for that--along with 50+ points in HP/TQ. J.Rob
Click to expand...
Probably more than that. I've never had over $400 in having heads rebuilt, and wouldn't want to.
 
rigger3006 said:
i know its not recommended but its what i have to work with for now, thinking of putting 60cc 302s on wifes 72 340, the 915s i pulled off were 73ccs, she just wants a cruiser for around town, probably nothing above 4500-5000, unless i take it for a spin, ive also got 028 thin head gaskets for it and voodoo 60401 cam, 323s and a stock T|C with 727. dont beat me up too bad on this one!!!!
Click to expand...

'1972' 340/240 HP

Factory Specifications

Piston Type ................. Flat-Top w/Notches
Piston Height .............. .054" {Below Deck}
Head Gasket ............... .036" {Thickness}

Cylinder Head .............. #3418915
Valve Size .................... 1.88" Intake ~ 1.60" Exhaust
Combustion Chamber ..... 73.0 {Factory}

Compression Ratio ......... 8.5 to 1 {Factory Estimate}

'Swap Out'

By swapping on a set of 'stock' #4323302 Cylinder Heads with a Factory
Level of 63.5 {CC's}.

Compression should reach approximately ...... 9.4 to 1

~ Uh Oh Factor ~

Intake Port Size ............. .87" Width x 1.87" Tall
Intake Port Volume ........ 122 CC's
 
.055 in the hole..... that's sad...

The idea of a closed chamber head is the quench! above .045" there is no quench. You could bolt the head on without a gasket and not get any quench.
 
pretty sad intake ports !, 915s not much better when you actually measure them, ive got the 302s ported to that size with some work on the pushrod pinch. and we know how much we can trust factory estimate of compression ratios
 
rigger3006 said:
pretty sad intake ports !, 915s not much better when you actually measure them, ive got the 302s ported to that size with some work on the pushrod pinch. and we know how much we can trust factory estimate of compression ratios
Click to expand...
Well the factory rating which most people think was conservative on the 340s has it about 90hp above the 318s with a cam, manifolds, exhaust, and intake with T-quad different besides the 1.88 915s.

There's a big difference in ports between the 915s and 302s. 915s have a lot more meat to them for porting, start out with larger ports, start out with larger valves, and have the potential to support a whole lot more power. The 302s need the portwork because they lack it. The chambers may be smaller- but that's the case with many 318 heads. 915s can be milled, the big valves can be put in and all that's relatively simple, reasonably priced work to have done. Thing is- the compression has more effect than just what power it makes, and often times for a build that'll progress having decent power now and not having to change to less cut heads, aluminums, etc can be worth the while on a progressive build.

The Magnum ports are different- my recollection is they're intermediate from the two and wider.
 
rigger3006 said:
pretty sad intake ports !, 915s not much better when you actually measure them, ive got the 302s ported to that size with some work on the pushrod pinch. and we know how much we can trust factory estimate of compression ratios
Click to expand...

I believe the NHRA specs for the '1972' 340 are the following.

Piston Height ........................ -.054" {Below Deck}
Gasket Thickness ................... .036"

Cylinder Head {#3418915} ..... 64.7 CC's {Combustion Chamber}

Net Compression ................... 9.32 to 1
 
69 Cuda 440 said:
I believe the NHRA specs for the '1972' 340 are the following.

Piston Height ........................ -.054" {Below Deck}
Gasket Thickness ................... .036"

Cylinder Head {#3418915} ..... 64.7 CC's {Combustion Chamber}

Net Compression ................... 9.32 to 1
Click to expand...

64.7 cc is NHRA minimum spec. It takes a .040 cut to get there.
 
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