My 402 heads are listed for "366/427" - The 1947 - Present Chevrolet & GMC Truck Message Board Network

davepl · 01-02-2012, 04:35 PM

The casting numbers on the cylinder heads for my 70 GMC 402 are 3975950, which at every source I've checked shows them as

1968-70 366/427 2.06/1.72 Closed Chamber

The block is TO42TTBG, which is 402. Now I'm a little confused, because the 366/427 are tall-deck engines and the intake manifold wouldn't fit, even if you could mix and match tall deck heads with a short deck block.

Are the sites I've checked all wrong, or do I have the wrong heads on this truck?

Thanks!
Dave

**425HP409** · 01-02-2012, 06:56 PM

The heads will interchange between tall and short block. The .400" taller block puts the heads wider apart and that is why you must have a 366/427 tall block intake.

davepl · 01-02-2012, 06:59 PM

Thanks! And from searching, it appears these heads are not uncommon on the 396/402, just bad reference material I was looking at I guess.

**special-K** · 01-03-2012, 08:21 AM

They could have been replaced.

01-02-2012, 04:35 PM	#1
davepl Registered User Join Date: Aug 2006 Location: Redmond, WA Posts: 6,332	My 402 heads are listed for "366/427" The casting numbers on the cylinder heads for my 70 GMC 402 are 3975950, which at every source I've checked shows them as 1968-70 366/427 2.06/1.72 Closed Chamber The block is TO42TTBG, which is 402. Now I'm a little confused, because the 366/427 are tall-deck engines and the intake manifold wouldn't fit, even if you could mix and match tall deck heads with a short deck block. Are the sites I've checked all wrong, or do I have the wrong heads on this truck? Thanks! Dave __________________ 1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible

01-02-2012, 06:56 PM	#2
425HP409 425hp409 Join Date: Oct 2008 Location: Prosper Texas Posts: 841	Re: My 402 heads are listed for "366/427" The heads will interchange between tall and short block. The .400" taller block puts the heads wider apart and that is why you must have a 366/427 tall block intake. __________________ Charles 68 SWB, Dad bought new, now 396 & factory ac 64 Impala SS, 409 425HP, 4 speed AC 64 Bel Air Wagon, 400 Small Block 57 Bel Air all original 283 w/Factory Air 77 GMC Sprint, 454/425HP 67 Olds 442, all original 90 ZR1 Corvette

01-02-2012, 06:59 PM	#3
davepl Registered User Join Date: Aug 2006 Location: Redmond, WA Posts: 6,332	Re: My 402 heads are listed for "366/427" Thanks! And from searching, it appears these heads are not uncommon on the 396/402, just bad reference material I was looking at I guess.

01-03-2012, 08:21 AM	#4
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,852	Re: My 402 heads are listed for "366/427" They could have been replaced. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

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