69 L78...go pure stock or???????

[Chris_69_SS]

want to get away from the modified underhood 454 (600hp) and run an L78 complete with manifolds, .520 lift cam, 163 intake and all.

Before I get to specifics, the car will be an M20 as I am currently ripping out the TH400. I have 4.10s in it now but may or may not keep them.

My options are as follows:

1) keep the current 10.5 comp, Oval port 454 and add: 163 intake, L78 cam, 780 Holley, manifolds, 2.5 mandrel bent exhaust , 375hp sticker to air cleaner.
2) sell current 454 and build a 396 with the 163 intake, L78 cam, 780 Holley, square port heads etc...

Option 1 would be the cheapest and can be done with mill in the car. However, I could sell the 454 (been offered 6k) and go 396 right away.

My goals are to only track ity once a year and prob. on Drag Radials or bias ply tires. I'd be more than happy to run mid-low 12s with one of the combo's listed above.

A few more quesions:

I know 840's are the 69 iron Square port head. Are there cheaper altenatives from GM as a service replacement? I see 840s at 1800$ a pair on Ebay but find that pricey.

- Should I port the ex. manifolds? Do you recom. doing this at home?
- I suppose a scattershiled would be best?
- Should I get the L78 cam from GM OR do the Crane Cams Blueprint version?
- Fuel line sizes? Stock or a bit bigger?
- fuel filter? what do you run?
- Fuel pump? Is there a specific p.n. for the L78?

[Chris_69_SS]

anyone?????

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[VintageMusclecar]

Chris;

Any particular reason why you want to go to a 396 instead of staying with a 454-based shortblock? The car isn't a numbers-matching car anymore, right?

Just tossing out some thoughts to ponder over;

As far as a more affordable set of heads goes, you could look for a late `70 or later dated set of 291's, which tend to go for about 1/2 or less of what the primo dated stuff sells for. Only thing is, the 291's have the largest intake runners of all the original closed chamber rectangle port heads, which won't help matters on a 396-based shortblock in regards to torque, throttle response & overall driveability. That's where the added cubes of a 454-based shortblock would be a welcome improvement.

If you want to port the exhaust manifolds, you might want to consider Gessler head porting services.

A scattershield is never a bad idea, but you could probably get away with a regular 621 bellhousing and a quality 11" clutch set-up and flywheel. (A rev limiter would be a great idea as well in this regards)

re: The 163 intake--if you plan to run a 4346 (or similar) carb, leave the plenum divider intact. If you want a little extra sumthin-sumthin', you can cut the plenum divider down and run a factory L88 style vacuum secondary carb such as the 3418 which is rated at 855 cfm. I used that exact set-up on my own 496 with surprising results, which you can check out in the following link below if you're so inclined.

As far as the L78 cam goes, run the Crane blueprint cam with a set of EDM lifters and forget about it. If you feel like reading, do a search on the subject, it's been thoroughly discussed here on numerous occasions.

Stock 3/8" fuel line is fine, and you can even use the original-style 5/16" feed lines into the float bowls, assuming you plan to run a reproduction L78 style fuel line. My 496 ran perfect with those lines on the dyno making well over 500 HP, and the BSFC numbers even showed it to be running a little rich.

Fuel filters: See above re: my 496--it had the factory sintered bronze filters inside the float bowls during those dyno runs as well.

Not sure on a factory P/N for the L78 pump, but lots of people have had good results using a Carter street/strip mechanical pump (don't have the P/N handy to those either, but you should be able to look them up easily enough)

Hope that helps.

Eric

[Chevy454]

Eric pretty much nailed. I wouldn't worry about porting/extrude honing your exhaust manifolds...there's easier power to be had elsewhere, and you're gonna waste a lot of time/money and have little to show for it. Also, if you're gonna run at the Pure Stock events, you'll have to ditch the 454 for a correct 396 mill, or move to the "Stock Appearing" class...

[Chris_69_SS]

Eric, great link. Thanks. Rob, thanks too for your input.

I currently run a very similar cam set up to the 496 with the ubiquitous 99893 CC springs. Heads are ported 049 ovals with BIG 'ol valves.

I think keeping the cubes at my present 454 is best idea and next rebuild going 489/496 would be an option. Hey, that's why they make 396 air cleaner stickers, right?

Did you re-dyno that setup with manifolds? It'd be interesting for sure. I'd say a 50hp loss, as a best guess.

So, all said, I will keep 'er as is and just nail down some detailing stiuff to make it even more stealthy....I best get my $$$ out of the 600 hp 454 I have before re-working the combo. I guess I'll have to do with 120+ mph trap speeds for now!!!!

[Wardy]

Wouldn't option 1 result in a square/oval port mismatch? I've read where this can actually work OK, bit there really shouldn't be a reason to do it in your case.

[VintageMusclecar]

Chris;

I didn't bother with trying to run manifolds on the 496 because that cam would never in a million years work with them. I would guess the power loss with that cam would've been at least 50 HP, probably considerably more.

[ QUOTE ]
I think keeping the cubes at my present 454 is best idea and next rebuild going 489/496 would be an option. Hey, that's why they make 396 air cleaner stickers, right?

[/ QUOTE ]

Sounds like a plan.

Eric

[agtw31]

if youre only going on the track once a year,throw some manifolds on,change your cam,keep what you have,and get a scattershield and a real good loop.

[VintageMusclecar]

Chris;

Here is a pair of service dated 291's on eBay that seem to be a decent deal.

Eric