ironheart1

Hey guys.

A couple questions. My 'bird just arrived last night and I've been hard at work going over it since. The previous owner neglected to mention a very loud ticking noise that goes away after 2000RPM or so (lifters, I would imagine), but that's not the point.

The engine in the car is a '73 400 rated at 170hp. What were the differences in these engines from the older ones that so thoroughly neutered them? Can I do anything to remedy this? There is currently NO smog stuff on the car whatsoever as far as I can tell so I'm curious what else I can do.

msbz_ls1

iTrader: (1)

from what ive heard..is...the 60's were great everyone had the muscle cars..gas was cheap...then when the 70's..started..Vietnam was goign on hard..and gas prices were shooting up...so all the cars..were bogged down..smaller engines were put in them..to conserve more gas...i think ur car falls under the year..of...we need something with high mpg if were gonna sell this year

ironheart1

I understand that, and you are correct. However, I'm curious about what differences exist in a '73 400 that are not present in a '70 400 that give it such lackluster performance, and what I can do to give my '73 400 the performance of an earlier engine.

Hambone 7

i read an article in Hot Rod magizine that had a build up of what i believe was a 72' 400. even with the addition of a 750 cfm carb torquer II intake and longtubes it only gained lie 15 hp. the main performance booster was a higher compression ratio bottom end, and a really mean cam, after that they were making some really impressive numbers, up around 375hp if im not mistaken.

VIP1

Engine ratings also changed from SAE Gross (1960's & earlier) to SAE Net (late 1960's or early 1970's and later). This accounts for some of the drop-off in the power rating. The rest is different parts. This is from memory... lower compression, less free flowing heads (I think EGR was added, I dont remember), smaller cam, and I think a different intake. I dont know about the exhaust. I think the block is basically the same.

1999T/A

iTrader: (4)

The main difference is the heads . The heads from the 60s , early 70s were High compression, high flow heads , meant to run leaded gas . They changed all of that in 72-73 . Low compression heads that flowed ok went on them and neutered them . Get you some 1969 #16 heads and bolt them to that 400 . You will have to run super unleaded with some race gas mixed to prevent detonation because it will be about 10.5 - 11:1 compression , but you will be pushing 380 HP at the crank and close to 500 ft lbs of torque . I know , I built one . Damn thing ran like a raped ape and shredded the tires when it shifted into third gear . Man I loved that motor .

Edit : I also used a ram air 3 grind aftermarket cam . I still have the cam card , cant believe I still have it after all this time .

Firehawk0220

More strict emissions control devices were added and the lower compression heads and smaller cams were the reason for real decline. The SAE Gross HP rating accounted for the main number drop. 1/4 times didn't change that much in reality.

All T/A's and Camaros run sub 15's as far as I know. Every year does. Of course there were many years that were as good as the low 13's.

ironheart1

Ok, so my question is this, then, simplified:

Does my '73 400 have the same potential, if I were to tear it down and do all new internals, as a '69-'70 400?

VIP1

I think the block is the same, but I dont quite remember.

If so, then yeah it whould have the same potential.... with new heads/intake & carb/exhaust, maybe even with higher compression ratio pistons (less dish, no dish, dome, whatever).

I dont remember though. If no one on here can answer this, a search on google will probably turn up some results.

Firehawk0220

If you dump the stock heads then I'd say yes. Even machine and rebuilt those heads aren't likely to flow as well. The lower compression heads that were out in the mid 70's just weren't as good as prior castings. From what I've read anyway.