If someone did not want to alter the stock compression ratio on their 225 but wanted to add a four barrel intake, long tube headers, a higher stall converter, shift kit and steeper gears like 3.91's in a Duster and end up with a lively slant, what cam/specs would you install?

The stock '71+ up mechanical cam, the 244° duration Mopar Performance cam or the mildest of the Erson RV grinds is all I'd use with the stock compression ratio.

I wouldn't go any steeper than 3.55 gears either unless it was a track car or the engine will feel out of breath while cruising. You need to match the engine's operating range (as dictated by the axle ratio) to the cam and the cam duration is limited by the compression ratio.

You're leaving great potential untaped by not raising the compression ratio. Most 225s are below 8:1 as delivered. I checked one mid 1970s engine at 7.6:1. Would have been good for boost, but not for naturally aspirated performance.

I'm going to quote something I wrote 5 1/2 years ago:

"Even in this community a lot of people seek parts for parts sake and not to reach a HP or ET goal. I think David Vizard put it best when he wrote something like: "You don't want to own a drill bit. You want the hole." In the same manner you don't want a 4bbl carburetor and intake manifold, you want the increased performance. Where a lot of people go wrong is in buying parts they don't need, that don't help or help very little for the money spent (poor value).

The first performance slant I built was a performance failure. I had a Holley 390, Clifford intake, Clifford headers, Mopar 276°/.490" cam, forged +.030" pistons, high volume oil pump, roller timing set and electronic ignition. I thought I needed all that stuff, but didn't realize all that I had done wrong. The compression ratio was much too low, the distributor curve was wrong and it ended up eating the oil pump and cam gears. It had a really healthy sounding idle, but my '66 Dart was really slow.

After the cam and oil pump gear in that engine failed I put in a Comp 264° cam and a stock oil pump. The engine idled much better, was easier on the clutch and was just as fast if not faster. Recurving the distributor made it faster yet. When I finally got the compression ratio up and put big valves in the head the car really ran well. At this point I was road racing the car and poor oil control killed a rod bearing which took out the rod, a piston, the block and crank.

My '67 Valiant has a stock short block including the stock cam. I came into an Offy intake and a Holley 390 at a good price. I had a head milled for compression (it's all of 8.5:1), had larger valves fitted and ported the head myself. I had 2 1/4" exhaust with a Walker Dynomax Super Turbo muffler installed from the stock manifold to the bumper. Ignition is via a recurved stock electronic distributor and an HEI module and coil. This car is just as quick as my '66 Dart was and cost me a fraction to build. I may not have a real fancy drill bit this time, but I have just as nice a hole."

Put another way; just as good of performance results as proved by time slips.

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Joshua

Keeping stock compression and adding all those goodies may bring you less power and worse mileage.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

At which point he might as well throw a small blower into the mix & see what happens

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63 Valiant Wagon
225 - 4 bbl

Bang for the buck would be 2 bbl, better exhaust and a better timing curve. Much more than that and you really want to pull the head for bigger valves and a milling job to raise the compression.

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Joshua

Agreed

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Got it guys, Thankyou.
I was curious because I have seen a lot of the offy 4 barrel intakes used with the stock exhaust manifolds and wonder how that set up runs.
Recently my exhaust shop told me to run a four barrel and headers and it would make a world of difference....this is from some guys that remember these engines when they were younger. I'm not really sure how involved they were or hands on with an actual slant hop up. Just garage talk I guess.
I know that raising the compression, adding the correct cam and distributor recurve is missing from my equation above.
Thanks for your experiences.
I am pretty satisfied with my super 6 daily driver Valiant considering the mods I've done. It turns mid 17's which is a lot better than a stock slant 6.
I want to drop a couple more seconds with my next build!

Maybe check this thread to get an idea of what works http://www.slantsix.org/forum/viewtopic.php?t=23314

Dave

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86 Miser 170,000+
2 1/4" exhaust
Holley 1920 #55
HEI MSD BLaster 2
17.8 mpg

If you want to leave a good shortblock intact, focus on the cyl head first, with bigger valves, porting, and milling for compression. I have gone 14s in a light car and 15s in a heavy car with a stock shortblock. As said above, everything is in the whole combination, not individual pieces.

Lou

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Home of Slant6-powered fun machines since 1988

In my experience an Offy manifold is equivalent to the cast iron 2bbl manifold.

On a stock engine with the stock exhaust manifold, trap times were the same. The butt-o-meter said the Offy was better, but track times wouldn't verify that.

Until you do the cylinder head work, the only real benefits to the Offy/ 4bbl combo is that it looks cool & you enjoy fiddling with the carb.

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63 Valiant Wagon
225 - 4 bbl