The absence of piston choice unless custom made seems to be the occurrence. I have no problem with running a little higher than 10.5 to 1. I think If I run 91 octane pump gas through detonation shouldn't be an issue, the ignition timing may be more retarded than compared to the lower compression. Also a longer intake duration could be used to bleed of cylinder pressure and change the dynamic compression or a stock cam grind could have the timing retarded. But I think I'll be fine with the 91 octane
budget 273 build
- Thread starter JJR
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I would not run a Torker intake. 318's and 273's have smaller intake ports than 340's and 360's. If you want a single plane, I'd go with a Holley Street Dominator or Offenhouser. But your best bet would probably be dual plane Performer, Mopar, or Weiand. A word of advise would be to keep your old AFB. After trying other carbs, you may find the old AFB works the best on the 273. Remember it is all about the combination. If running stock exhaust manifolds, I'd recommend a dual plane intake and a cam between 260 and 268 duration with springs to match along with a double roller timing chain. Get a good distributer with about 25 degrees of mechanical advance and set initial timing at 10 degrees BTDC. These mods would work with your 2 barrel pistons or 10.5 replacements. All things being equal, your 273 will rev higher than the numbers given by intake and cam manufacturers. If you are running higher than 5,000 RPM, and you should, I'd use a high pressure oil pump spring and a windage tray. Lower compression at full advance will run better than higher compression with retarded advance.
Yeah I was wondering how large of runners the edelbrock torker has, and is there a difference between runner size in the torker 2. I wanted to stick to the stock manifolds instead of headers because the headers are 1-5/8 inch and that seems to large for this engine especially when I only plan on turning it 6000rpm. 260 degrees as in advertised or effective duration? If you can, can you explain why the lower compression with more advance will make more power and is there a happy medium? Because it wouldn't make sense that going to a 9 to 1 or a 8 to 1 compression and jacking the timing would make more power than a 10 to 1 with the appropriate timing.
The Torker 2 still has 340 runners.
260 is advertised.
Most small blocks will run best at 35 degrees total advance. If you build a motor with 10.5 compression and have to retard the total advance to 25 because of detonation, a 9.0 compression motor with 35 degrees total advance will make more power. I have seen 10.0 compression motors where the top rings turned into 75 ball bearings. It leaves an impression. If you want to try and play with dynamic compression to get your compression down, that is another can of worms. Just remember, you only have 273 cubic inches, a bigger cam is not street friendly. You want to build as much torque and mid range as you can. It should rev to 6,000 rpm easily.
260 is advertised.
Most small blocks will run best at 35 degrees total advance. If you build a motor with 10.5 compression and have to retard the total advance to 25 because of detonation, a 9.0 compression motor with 35 degrees total advance will make more power. I have seen 10.0 compression motors where the top rings turned into 75 ball bearings. It leaves an impression. If you want to try and play with dynamic compression to get your compression down, that is another can of worms. Just remember, you only have 273 cubic inches, a bigger cam is not street friendly. You want to build as much torque and mid range as you can. It should rev to 6,000 rpm easily.
Timing is Timing all it is used for is to get the spark to happen at the right time so you can build the highest combustion pressure possible when the Piston is near TDC. So if you had the same setup on two different engines and the only difference was compression ratio. The Higher Compression Engine would need less timing for a given fuel because pressure and heat would build to fast and the entire mixture would instantaneously all combust before the piston hit top dead center(detonate) an cause to great of an opposition to crank shaft rotation to be safe for the engine. So on both engines you can only build so much pressure just before TDC to prevent detonation. At and after TDC the Highest Pressure Possible is the goal. So wouldn't the higher compression make higher pressure. Fuel Efficiency would also increase to wouldn't it?
In practice, without getting into the complexities of combustion, there is a total timing setting that will produce the highest horsepower and lowest ET. It, typically, will only vary by a couple of degrees for an engine, this is why it is so important to find true TDC. It may be different for another engine. SB Mopar is around 35 degrees, an early Hemi is about 30 degrees, BB Mopar is around 38 degrees. If you build an engine with too much compression and have to back down to 25 degrees (Total advance, initial plus Centrifugal advance) to stop detonation on a SB Mopar, you will make less power and be less efficient than a 9.0 CR SB Mopar with 35 degrees of total advance. The problem is with the available pump gas, if you are driving on the street. 93 Octane pure gas if you are lucky, 91 with alcohol if not. A race car is much easier. You can get good gas, and you are only burning it 1/4 mile at a time. You have to look at the total package or you may end up with an expensive dog. Be realistic with what you want to do with your car, and talk to your cam company before you buy anything.
In my experience, you can run the high-compression 273 on 91 octane, with only dialing back the initial timing one or two degrees (I think I have it at 12 BTDC). There's a lot of quench area in the stock head.
Changing the subject, I think there's a lot to be said for the AFB and the stock Commando single-plane intake (other than its massive weight, that is). It basically incorporates 3/4 deep spacers (or ram tubes, if you will) for each carb throat -- you don't get that with aftermarket setups. It keeps the velocity up, and I think it contributes to its incredible responsiveness. Just a thought...
Changing the subject, I think there's a lot to be said for the AFB and the stock Commando single-plane intake (other than its massive weight, that is). It basically incorporates 3/4 deep spacers (or ram tubes, if you will) for each carb throat -- you don't get that with aftermarket setups. It keeps the velocity up, and I think it contributes to its incredible responsiveness. Just a thought...
That 273 leaves hard.
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