Building a 273

-
Quick is torque, Fast is rpm. Sounds like Babyblue66 wants quick. 3,000 rpm is where most good 273's and 340's come into their power band.
I find funny when people compare smaller and larger but with the smaller engine severely under geared.


Here's just a general statement to whom it may concern :)
And not against the OP's build.

Since 3.23-3.55 seem like the go to performance gear which is generally a compromise gear for most cars eg. 3.55 @ 100 mph with 28" tires = 4260 rpm maybe 4500 rpm with torque converter slippage a 3.23 would be about 400 rpms lower. 4500 rpm is well below most performance engines peak hp rpm especially smaller the engine, making good power. A peak hp at 4500 rpm would be about .08-.09 per cid would be a good hp goal if you wanted 3.55 be optimal. A good converter can help alleviate especially the closer peak power is to peak gearing rpm.

Part of the problem is what's optimal gearing for best acceleration, for the track is easy to calculate but for a street only car there's no goal post maybe best zero - 60 mph or 80-100 mph maybe more to me gearing for a 100 mph is a good number to gear for max street acceleration obviously building cars come with comprises but it good to figure out how compromise your choose is and maybe instead run a compromised gear could compromise engine choice or hp goal etc.. Or a bit of each for a less overall compromised situation.
 
What of a 3.91 SG. Is that in alignment with the train of thought?
Depends what's the combo but it's about 450 rpms more than a 3.55 gear so closer to 5000 rpm @ 100 mph.

It's just seem like most think one size fits all or at least has the same effect no matter the cid, eg.. a 225 vs a 440 both making 300 hp the 225 would basically need to be about twice as deep as the 440 gear to be on par.
 
Depends what's the combo but it's about 450 rpms more than a 3.55 gear so closer to 5000 rpm @ 100 mph.

It's just seem like most think one size fits all or at least has the same effect no matter the cid, eg.. a 225 vs a 440 both making 300 hp the 225 would basically need to be about twice as deep as the 440 gear to be on par.

It's actually sitting behind a 225 now but contemplating a 273 swap so I'm watching this thread develop. Thanks
 
It's actually sitting behind a 225 now but contemplating a 273 swap so I'm watching this thread develop. Thanks
273 has way more potential than a 225, 273 head flows more stock than a 225 ported and has to more intake ports to boot :)
 
It's actually sitting behind a 225 now but contemplating a 273 swap so I'm watching this thread develop. Thanks
If i was to do a 273, aftermarket stock replacement magnum heads, notched zero decked block, knock off air gap with 650-750 carb, headers and 220 ish cam on 110 .500-.550 lift
 
If i was to do a 273, aftermarket stock replacement magnum heads, notched zero decked block, knock off air gap with 650-750 carb, headers and 220 ish cam on 110 .500-.550 lift

I have other priorities currently but the engine sits in the garage awaiting inspection. It's complete and appears to be in very good condition. 65 casting

20221213_115123.jpg
 
I have other priorities currently but the engine sits in the garage awaiting inspection. It's complete and appears to be in very good condition. 65 casting

If you have a 273, no need for special parts. The heads are good, They are closed chambers flow like 360 heads with just a bowl clean up. Get a set of stainless exhaust valves, double roller timing chain, and a cam and matching valve springs. The cam is the most important, since too big a cam shifts the power curve higher in the rpm. Early 273's 4 speeds had a 3.09 first gear which also gets you started quicker. I always liked the 65 Commando exhaust if using the stock exhaust manifolds.
 
Last edited:
If you have a 273, no need for special parts. The heads are good, They are closed chambers flow like 360 heads with just a bowl clean up. Get a set of stainless exhaust valves, double roller timing chain, and a cam and matching valve springs. The cam is the most important since too big a cam shifts the power curve higher in the rpm. Early 273's had a 3.09 first gear which also gets you started quicker. I always liked the 65 Commando exhaust if using the stock exhaust manifolds.
Note: The HP single exhaust was available from 65-67. I have read the early 65's didn't have a muffler just the resonator.
 
-
Back
Top