396/402 with PP heads tow rig build advice

5akman

New Member
I'm getting ready to rebuild a 1980 Chevy K20 for a flat bed fish hauling truck on the beach in Alaska. Current (non stock I believe) engine specs out at a 396/402 3969854 casting with -950 heads. This will be mated up with a Th400 trans with 4.10 gears and 33" tires. I do not yet have the engine out of the truck to confirm bore diameter.

Engine runs but I have zero history on it and I'd like to go through it prior to driving it up from CA to AK. I'm curious as to a cam/head/intake combo for this low speed/torque monster that will be hauling up to 4000lbs of salmon a half mile or so across the beach in 4 low and then about 5 - 7 miles down the paved highway at 55mph to the processing plant.

I also have some peanut port heads (236 castings) that have had some minor clean up done to them, screw in studs and 3/8" guide plates installed.

Carb options on the shelf in the garage are a Holley vac secondary, Qjet and Edelbrock Thunder AVS (650 cfm).

So, with the above info in mind, I'm looking for advice for pistons to use with either the 236 or 950 heads and a cam recommendation. I'd also like to stick with 87 octane fuel.

I've read the peanut port threads but have not seen anything addressing those heads with a 396/402 build.

thanks,
Lance
https://www.facebook.com/alldrinsalmon/
 
If your intention was to maximize lower rpm torque in a 396-454 with peanut port heads , for use in towing a heavy load, at lower speeds,
they are certainly designed to do that, I.d say peanut port heads and a mild cam (similar too but certainly not limited to this one, obviously you,ll want to verify the dynamic compression ratio and clearances)
https://www.ebay.com/p/Elgin-RV-Torque-Cam-204-208-Dur-459-459-Lift-Chevy-BB-454-427-402-396/527980219?iid=221927971154&_trkparms=aid=222007&algo=SIM.MBE&ao=2&asc=45727&meid=872dbfe416c442df910d78c5df826a81&pid=100005&rk=4&rkt=6&mehot=lo&sd=152577237193&_trksid=p2047675.c100005.m1851

and ideally about 9:1 compression would be about ideal for your intended application.
long tube 1.5"-1.75" headers similar to these, and a low restriction exhaust would help.
http://www.carparts.com/details/Chevrolet/K20/Flowtech/Headers/1980/F3111500.html?TID=bngpla&origin={adtype}&gclid=CICK9qnA-dUCFQ2DMgodaWwCcQ&gclsrc=ds

wieand makes a specific intake to maximize peanut port head flow, in the lower and mid rpm ranges
https://www.summitracing.com/parts/wnd-8122p/overview/

wnd-8122p_xl.jpg
 
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Grumpy,
thanks for the info. Any suggestions on piston options to get to around 9:1 compression with the peanut ports?
 
346236 1975-87 454 Open 113cc . combustion chamber PEANUT port

https://www.uempistons.com/index.php?main_page=index&zenid=18baf65efed30844a5c5094bb9ce8435&cPath=3_4_23&sort=5a&filter_id=4&eng_filter=396/402&rod_filter=

http://www.wallaceracing.com/dynamic-cr.php

dynamic compression should ideally be in the 8:1-8.1:1 range

try to get the quench distance in the .040-.044 range
with the 113 combustion chamber a 15 cc-17 cc dome gets you near 9:1
hyper-eutectic pistons would be fine here.
I would try to find a 4.20-4.3 diameter head gasket

obviously ask the manufacturers tech dept,
if they have any suggestions and if they have had and clearance issues using your part number cylinder heads with the pistons your about too order,
just to reduce any potential problems,
and yes you\ll want to manually verify piston to valve and piston to combustion chamber clearance
s
valclear2a.jpg

related info

http://garage.grumpysperformance.co...alves-and-polishing-combustion-chambers.2630/


http://garage.grumpysperformance.com/index.php?threads/checking-piston-to-valve-clearances.399/

http://garage.grumpysperformance.co...-peanut-port-big-block-combo.2900/#post-61085

http://garage.grumpysperformance.co...2-bbc-with-stock-auto-th350.12999/#post-67614

http://garage.grumpysperformance.co...r-piston-dome-or-port-volume.2077/#post-61068

http://garage.grumpysperformance.com/index.php?threads/porting-can-help.462/


stamprockf.jpg


https://www.cartechbooks.com/techtips/how-to-build-chevy-big-blocks-cylinder-head-guide/

496mkl.png

peanutr1.jpg

peanutr2.jpg

peanutr3.jpg
 
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