TECH: Increasing CR on 73 351C

The first question is if increasing CR is what you really "need" to do... Pistons is one good way,,, not knowing if you are ready for a rebore is a PITA... Cylinder heads can do it but there are other considerations.... Increasing the compression ratio will offer up other very real considerations in light of available gasoline quality... Artificial aspiration is a way of theoretically increasing compression ratio.

There are a lot of very smart people on this NG... if you spell out what you expect, what you are willing to spend (this is the most important part), some details about the car (weight, weight bias, gearing, trans, and so on, and so on... this ain't no little thing if you plan on being happy with your "package").

In the FWIW department... this is some pretty old technology your dealing with... I get to play with a small fleet of old Mopar big blocks and the parties involved are into "nostalgia".. yes, these cars are very strong but there are a lot of "off the shelf" new cars that can almost equal their performance with none of the hassles...

Your question is too open ended when we consider the out of pocket expense you will realize attaining your goal...

Let me be more clear. Im trying to keep the car stock as possible. The car has original heads, ntake, carb etc. I know the 71 engine has more HP due to the fact Ford detuned the 72 a bit and the 73 alot.

snipped-for-privacy@webtv.net (Gary Vitagliano) wrote in news:22139-44597C15-679 @storefull-3211.bay.webtv.net:

Here's an excellent place to ask your question:

Some very knowledgeable folks in there.

The cheapest way to increase compression is to bolt on a set of Australian cleveland heads. They are available on ebay and a lot of other places. They have a smaller combustion chamber and an excellent intake port for good torque. Remember this is old technology. There are better (and more expensive) ways to make horsepower.

The reason for the "detuning" was because of the new concerns imposed by unleaded gasoline... tetra-ehtyl lead was, quite possibly, one of the best octane improvers/ detonation suppressors available. If your whole power enhancement plan hinges on upping the compression ratio of the engine, you are sure to be disappointed...

Additionally, the lead in the gasoline lubricated the exhaust valve seats allowing cast iron seats and valve rotators.. another consideration when using old technology engines.

The 351C 2V and the 351C 4V had some significant differences.... One other salient point... after the introduction of no lead gas, the Cleveland engine family died quite suddenly. Replaced by the 351M/400 family, which also didn't last a significant amount of time - especially when compared to the long lived Windsor engine family...

Well Im open to Ideas to increase HP but the motor MUST appear stock. Anyone use those MPG port plates? Will the aussie heads take my intake / exaust manifolds?

snipped-for-privacy@webtv.net (Gary Vitagliano) wrote in news:4328-445AC325-924 @storefull-3216.bay.webtv.net:

Ah, you're racing it?

They aussie heads will take your stock intake and exhause manifolds. They look like Ford heads because they were Ford heads, in Australia. Not quite sure of your intent here, but if you want it to appear stock, they will work until somebody pulls a valve cover and starts looking at part numbers.

How much HP increase? Just what the f*ck is it you want in easily identified measures??? More bottom end grunt? top end snort? Are you after a car that is quick or a car that is fast? You can make a car seem to have more HP with gear ratio and suspension changes....

You must realize this.... when you modify a car, the only way to spend money wisely is to decide on your "package"... To this end, we decide, first, our budget... then we decide what we want to achieve.... then, we spend our money in the best possible manner to get as close to our goal as possible....

I am not tryng to be counterproductive.... OTOH, you haven't given us any idea of what you want other than the appearance angle. This rules out headers, most intakes, power adders and most carburettors.... Without a little better idea of the goals, this thread is about to turn into a waste of time...

FWIW, everyone wants horsepower... you can get horsepower only to find that it was torque you were after.... Hint... There is no replacement for displacement...

Im looking for more low end grunt. I want it to look stock since the whole car is 100% stock. Ill look into Aussie heads and / or MPG Port plates.

snipped-for-privacy@webtv.net (Gary Vitagliano) wrote in news:5769-445E0D2C-1126 @storefull-3212.bay.webtv.net:

Aussie heads are NOT the way to go for low end grunt. They are free breathing and are meant to rev. Your best bolt-on option for more low end would be an "RV" cam that moves the power band down lower.

The Aussie head ports look much smaller than the monster ports on my engine. I thought smaller ports = low end torque.

"elaich" wrote

RV cam? Geeze that's a caveman term. How bout a 3/4 race cam. digging back in time for outdated terminology. :)

Go to one of the bigger camshaft manufacturers websites and check out what they have. They will usually show what the grind specs are and what can be expected from the cam in terms of performance, and which setup the cam is made for.

Or you could go here where I've already brought up a generic cam search for that engine at Summit Racing. You can click on what type of performance you're looking for and it will bring up the cams fitting that description.

MPG Heads also makes custom grind camshafts and will set you up with exactly what you need based on what you want. Give the guy a call. I've talked to the shop before. It's just across town here in Denver.

You're welcome ;)

I would have to disagree on that one. Let's review the cleveland head specs. The American two barrel heads had perfect intake runners for low end RPM, but had huge combustion chambers. The American four barrel heads had the good combustion chambers, but had huge intake runners, actually too huge for low end torque. It's the American four barrel heads that were built to rev. The Aussie heads have the best of both (factory) worlds. Smaller intake ports and smaller combustion chambers. Also, occasionally an Australian factory 4V intake will be sold on ebay that was factory for these heads. That is rare, however. Properly built, these Aussie heads have plenty of low end grunt. The original poster wanted more compression. These heads will do it, but only to a certain point, maybe 1/2 to 1 point raise. Once again, there are better choices out there, but the original poster wanted a stock looking head.

3/4 cam, that's funny I was just mentioning to my friend what non sense that term was.

I just put a pair of Aussie heads on my '72 mach 1's 351C. The Aussie heads will in fact bolt up to the intake & exhaust fine, BUT, they don't look identical to American Ford heads, however. The American 2V heads have the cast "2" at the top of the head on the same plane as where the valve cover bolts are and the Aussie heads have the cast "2" at the bottom of the head, near the block. They'll know at a show in an instant if you have Aussie heads. I put 'em on anyway 'cuz they're awesome!!!

-Dave

So the heads gave you a noticable improvement? Did you have a original

4V car?

The car was orginally 2v, but someone had put 4v heads on the 351C. The 4v heads were "open chamber" heads and I didn't want to deck them to increase the compression. The 2v Aussie heads are closed chamber and still have the smaller ports (like the American 2v heads) to help reduce fuel consumption. You won't be disappointed if you go with the Aussie heads.

Dave

Dave please e-mail me directly please.