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| Jetting 170 vs. 225 https://www.slantsix.org/forum/viewtopic.php?t=25448 |
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| Author: | ValiantOne [ Fri Oct 19, 2007 7:37 pm ] |
| Post subject: | Jetting 170 vs. 225 |
It dawned on me tonight that I am using the carb off of the 170 engine that came out of my car, on the 225 that I put in the car. Is the jetting different between the two? Do I run the risk of running too lean and hot? Also, what is the single adjustment screw at the bottom of the Carter BBS. I bought my FSM for the 79 engine. No BBS info there:) Thanks guys, Chris E. |
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| Author: | Doctor Dodge [ Fri Oct 19, 2007 8:11 pm ] |
| Post subject: | |
A 170 BBS will have a smaller 1 9/16th throttle "blade". (butterfly) The jetting will be correct but the carb will flow less air. The screw at the base of the carb. is used to set the idle air / fuel ratio. DD |
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| Author: | SlantSixDan [ Fri Oct 19, 2007 9:14 pm ] |
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There's no jetting incompatibility. Elaborating on what Doc says, the 170 carbs used through '66 had a 1-9/16" throttle bore. This small-bore carb was also used on taxi-spec 225s to save on fuel. The larger 1-11/16" carb was used on regular 225s, and on 170s starting in '67. You can measure the throttle bore diameter at the bottom of the carb to determine which size you've got. Of course, at this late date the odds are against your looking at any particular engine's original carburetor. |
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| Author: | Charrlie_S [ Sat Oct 20, 2007 5:36 am ] |
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The 1965 automatic trans, 170's, had the larger carb, also. don't know about other years. Had to prove this to NHRA back in 1974. |
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| Author: | SlantSixDan [ Sat Oct 20, 2007 9:38 am ] |
| Post subject: | |
Quote: The 1965 automatic trans, 170's, had the larger carb, also.
My '65 FPCs and FSMs say they got the smaller one, but it's entirely possible some of each left the factories.
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| Author: | Charrlie_S [ Sat Oct 20, 2007 2:18 pm ] |
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In 1965 the 170 standard shift got the small carb. The 170 automatic, and all 225's got the large carb. |
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| Author: | Dusty Desks [ Sun Oct 21, 2007 6:35 pm ] |
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Theoretically, the smaller carburetor is more efficient because of better vaporization efficiency in the narrower venturi. Peak horsepower at wide open throttle at high rpm is reduced 5% with the 1 9/16 carburetor vs the 1 11/16. Even the large carburetor is rather small even for a 170 engine; they used these for low initial cost, trying for the best compromise of efficiency vs. power in a single venturi design. This is why people get such good results with the 2 bbl. "super six" carburetor; the two venturis are each smaller than the one on the single bbl., but the total area for two is greater. Therefore, better efficiency and greater maximum flow, both, but more expensive to manufacture. Slant six carburetors also suffer because they had to be specially designed for these cars (low height), hence a short venturi, to fit under the low hood, for body styling purposes. Long venturis are more efficient, and tall carburetors were common on old cars with high hood clearance. |
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| Author: | ValiantOne [ Mon Oct 22, 2007 5:25 am ] |
| Post subject: | |
Thanks everyone. Great info! Chris E. |
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