pistons and cam selection

[leothelab]

Hi I am new to the hemi world and i am starting to tinker around with the 392 i had sitting in my basement for a while (dont have a vehicle to put it in but tinker i must) I am stopping my self at a hot street motor. I just wnat to put in arp rod bolts and mybe new main bolts. My questions are 1. can I get away with a 10:1 cast piston (stock heads) and not have to retard the timing. and 2. Cam selection. Has anyone experienced the thumpr cam. (noticable idle but still drivable. 3. who is a reliable supplier of hemi parts? thanks in advance.

[mart]

First, congratulations on getting a hemi and welcome to the group. Hemis are great engine and you should get all the help and advice you need here to build it anyway you want.

Since you're new to hemis, my first bit of advice is make sure *exactly* what you've got before you tear into it and start buying parts. I'm not saying yours isn't, but for some reason, a lot of people automatically assume that any and all early hemis are 392's. Besides the 392's - (which is 'high-deck' engine by the way and comparatively rare, as Chrysler *only* used then in passenger cars and *only* in 1957 and '1958) - there were the 'low-deck' 331 and 354 Chryslers, in car, truck, industrial and marine variations - as well as both high and low-deck Dodge and DeSoto hemis - which are also completely different from each other and from their Chrysler hemi 'sisters'. If you post the numbers - usually stamped on a pad at the front of the block- or on an industrial engine, usually on a tag riveted to the side of the block - people here will be able to tell you exactly what you've got.

About your piston question. Stock-replacement-type, 10 to 1 compression pistons should be fine for the street on normal unleaded premium gas without excessively retarding the timing. Hemis, by the way are naturally less prone to detonation for a given fuel octane, compression ratio and degrees of ignition advance. than engines with conventional 'wedge type' combustion chambers. If the motor's going to get a lot of use - and particularly, hard use, on unleaded fuel, I'd think about installing hardened valve seats and swapping the stock valves for some good aftermarket stainless-steel valves.

I can't speak for the so-called "Thumper" cams, one way or the other, but you should probably hold off on choosing a cam anyway, until you figure out exactly what kind of vehicle you're going to put your engine into. Intended use, vehicle weight, tire size & gear ratio. transmission type - ie - stick or automatic - and if an automatic. converter stall speed - are all factors that need to be considered when selecting a cam and can make or break a given combination.

About fasteners. New ARP rod bolts are definitely a good thing. Stock original main cap bolts, unless there's something obviously wrong with them, are probably fine. ARP and a several other companies make chrome-moly studs for the main caps, but they're overkill and not needed on the street - especially on a near stock 'performance rebuild. If I was going to replace any of the major fasteners, rather than new main cap bolts, I'd probably get new head bolts - or if you're really "bucks up", some aftermarket chrome-moly head studs - although again, if there's nothing noticeably wrong with them, even the original stock head bolts are probably fine for what you're doing. As you get into this project, you're going to find out that hemis, compared to a lot of other, more common engines, cost a lot more to build, so save your your money by not spending it on a unnecessary parts, so you'll have it to spend on the stuff you really do need Good luck with your hemi build and keep us informed.

mart
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[George]

As was said about engine size, if you don't have a list of casting numbers & use codes, post them here & we'll tell you what you got, unless your sure! A 10:1 hemi can run on the same octane that a 9:1 wedge does, should be good. Part supplyers: Quality Engineered Components, TR Waters, Hot Heads, though there have been complaints about his moded oil pumps & int shafts on other forums. Reportedly the "Thumper" is a poser cam that makes noise w/o the go. Never seen any results like dyno on them.

[leothelab]

thanks for the response and yes all my numbers checked out the web is a beautiful place for that, I guess I was putting the horse before the cart with the cam. I guess I was thinking more along the line of I had a 440 with a purple shaft and a sbc with a comp cam 280 degree (230 @ .050 with 480 lift) that both ran great but does the hemi need as much lift and duration as other motors to make power at the same rpm. I was just looking at the Keith Black Hypereutectic Pistons catalog. they list different head volumes. I have head # 1731528-1 does anyone know the chamber volume? Again the horse before the cart. I havent called the shop to check on my block I had it checked for cracks. again thanks for the responses

[George]

Hemis don't need as big a cam as a wedge.

[George]

http://www.jalopyjournal.com/forum/show ... tech+index

Go here & start reading!

[mart]

[quote="leothelab] "...I was just looking at the Keith Black Hypereutectic Pistons catalog. they list different head volumes. I have head # 1731528-1 does anyone know the chamber volume"[/quote]
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Just a word of caution about "hypereutectic" pistons. If you're just going for a very mild street build, they're probably ok. But if you want to build any kind of serious high-performance engine, stay away from them. Despite the hype and using the late Keith Black's name and reputation as a marketing tool, hypereutectic pistons - which are actually made by a company called "Silvo-Lite" - are *not* in any way a racing or even a 'high-performance- type" piston. The term "hypereutectic" refers to the fact that these pistons - which are all cast and not forged, by the way - do not expand as much, as they heat up, compared to either a conventional-alloy cast or particularly, a forged piston. This allows for a tighter than normal piston-to-wall-clearance, which improves exhaust emissions (which was the real design intention of these pistons in the first place) and - especially compared to a forged piston, makes for a somewhat quieter running engine. The problem is that to achieve this low expansion, so-called,"hypereutectic" quality, they're cast using a very-high-silicon-content aluminum alloy, which makes the pistons brittle and prone to cracking *if* the engine experiences any amount of detonation. If you can afford them, I'd look for a forged piston from a company like J.E., Arias or Ross - or short of that, if your budget doesn't permit a forged piston - even a normal *conventional-alloy* cast piston from someone like Egge.

mart
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[DavidBraley]

Speedway Motors sells the Egge cast pistons for the 392. At something close to $280, they are a good deal. Not 100% sure of the compression, but they are claiming 10 to 1.

[392heminut]

I ran the Egge 10 to 1 pistons in my 392 and had no problems at all running pump premium unleaded. I had the distributor set up with 20 deg. advance and ran 10 deg. initial timing with 30 deg. total timing, all in by 2500 RPM. I never had a pinging problem with that setup. The cam was the same as your Comp cam, 230@ .050 and 480 lift. My 1731528 heads had a chamber volume of 106 cc's.

[leothelab]

thanks sometimes (more than I care to admit) you get in that mode of if a little is good then more is better when I already know that a cast piston motor would take a moderate amount of abuse and I dont have to spend 600'00+ on a set of forged pistons

[George]

On a 392 the C/R is good, even if it's a little lower than advertised, so the cast replacement pistons are fine. If I had a low deck Dodge or DeSoto with low C/R it would be an intirely diffrent matter. a 241 with nominal 7-7.1:1 measured out @ 6.19. Custom forged to what you need on something like that is well spent money.