L78 Dyno

[Furback]

I finished assembling my NOS L78 shortblock today. Put a pair of 69 840 heads on it and a 163 intake. The cam is original specs and solid. 3/8 pushrods and Crane race rockers. So other than the rockers the engine is exactly as an original would be. Standard everything. Also installed hardened valve seats and manley stainless valves. Comp cams springs. Should be dynode within a week. It will be interesting to see what kind of numbers the dyno sessions show.

[L78 Fred]

Let me know the numbers
I will be doing the same in the next 2 months
Fred

[Salvatore]

hardened valve seats really necessary?

[earntaz]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: [email protected]</div><div class="ubbcode-body">hardened valve seats really necessary?</div></div>

It's a toss up -- I've read pros/cons. If you will be running the livin' hell out of the motor for extended period of times -- hardened seats are a must. But if you're just cruzin' with occasional jumping on it you probably don't need to install.

Valved seats back in the day were induction hardened -- but if the valve seats are ground below this &quot;hardened surface&quot; erosion may occur.

I'm sure others will chime in on this ...

TAZ

[Salvatore]

doubt if either of these guys are going to run their car that hard. both will probably use a lead additive or some racing gas anyway. Don't like cutting into stuff that can cause problems later. Not necessary just like floating wrist pins arn't really necessary for street motors IMO.

[JRSully]

I put hardened seats in my 70 291 heads on the 70 L78, didn't want to deal with lousy gas issues and the engine gets hammered on regularly. My engine dyno'd at about 428hp at 5600 rpm, dead stock except roller rockers, pertronix and headers, orig intake, compression, 4557 holley, stock heads, nos 143 cam. You need somebody experienced to do the valve seats right, have to watch the water jackets

[earntaz]

Jim -- what did you do for valve springs? Stock LS-6?

TAZ

[JRSully]

Taz, I believe I used a very close to stock, dual valve spring. Consulted with Crane (roller rockers) and my engine builder, but I know they are very close to stock. All the hp is in by 6000-6500 on a stock L78 anyway, no need to rev it any higher than that, just asking for trouble. Roller rockers are the ticket on these engines (unless you need to have stock valve covers, but you can use a camouflage spacer)they really let the engine rev and are very durable. Valve train is the weak link on these engines. But mine (with this set up) has been bulletproof and I have adjusted the cam only twice in 6 or so years

[earntaz]

Copy that -- I agree with going crazy with valve spring pressure may cause hate a discontent ... just looking for trouble on a 95% street machice. I have roller rockers ...

Thanks -- TAZ

[L78Kiwi]

I am interested in hearing how you guys get around the high compression (11+/1 ratio)- low octane fuel problem. Do you modify the engine, such as install lower compression pistons or installer thicker head gasket, or do you run a fuel additive or have a source for higher octane fuel such as aviation fuel?
I have just pulled down the 427 (casting no.3963512, closed chamer heads, standard holley and winters manifold)I intend using in my 67. It was built as a race motor for a 68 vette and has not been run since the mid 70,s. On the whole it is in excellent condition and probably could be run as is....but it will need some modification for the street and modern fuels so if anybody has similar experience I would greatful for some advice.I have attached a photo of a piston.....anybodyseen pistons with this pattern embossed into the skirt before