two schools of thought: big air jets and small air jets...48IDA

[deano]

The 2074 in my first rail ran 37mm vents with a 145/F7/170 stack and made 155 hp on Vittone's dyno at 5500 rpm. 

My 2074cc in my old rail, with 10:1, an 125 Engle, Chase Morse 1-5/8, ran 37mm venturis, 145/165 with F7s. Ran 65 idles as well. Made exactly the same power as your's did on F&A dyno (air cleaners and stinger). Ran beautifully, except along the water/beach at Pismo where it used to pop at low rpm, but as soon as I got back in the dunes, it was fine. It would track along in second gear down to a high idle, and then up to about 5500-6000 clean. It was a done deal at 6200.

[Jim Ratto]

37mm motors are a lot of fun as drivers. In some ways, they seem crisper and faster than a 42mm motor. I'm sure in an all out drag race, the 42's would win hands down.

I remember being at Roger's shop in the late 1990's and there was a young kid working there that had a clean sedan with alloys, 2276, K8, Roger's heads and IDAs. Roger went somewhere and took the kid's car, and I was impressed with how crisp and snappy the motor sounded as Roger left the parking lot. When he came back he told me the secret was the 40mm vents. He said the kid wanted to go home and put 42mm's in it,  but Roger told him it would make a big hole in the power.

I've spent (wasted?) so many hours going back and forth with vents on the motors I've had in my cars, and I have to say, the 42's run "ok" but overall, I'd have to say the car always ran sweetest with 40mm's and locked up advance.

I ran my last 2165 (FK45) with 37mm's most of the time, and it was really sweet to cruise on freeway with, it just sort of floated along @ 75mph. But it was done at about 5800-6000 if I stomped it.
The 40mm would run thru 6800 in 2nd gear.

Rayburn's car seems to make good use of his 42mm venturies, as his car seems to pull like there's no tomorrow, idle on up to the orbit. Funny, by calculator... that motor could use a 46mm!

Santa, I want a dyno for Christmas. 

[Sarge]

The 2074 in my first rail ran 37mm vents with a 145/F7/170 stack and made 155 hp on Vittone's dyno at 5500 rpm. 

My 2074cc in my old rail, with 10:1, an 125 Engle, Chase Morse 1-5/8, ran 37mm venturis, 145/165 with F7s. Ran 65 idles as well. Made exactly the same power as your's did on F&A dyno (air cleaners and stinger). Ran beautifully, except along the water/beach at Pismo where it used to pop at low rpm, but as soon as I got back in the dunes, it was fine. It would track along in second gear down to a high idle, and then up to about 5500-6000 clean. It was a done deal at 6200.

Thinking back on it, when I built the 2332 for the second rail, I drug that out to Vittone's too.  I was expecting to change jets with the larger engine size and cam (125 to FK89) plus 12.5:1 compression but all remained the same and I think it made 175-180 hp at 6000 rpm.  That motor had 912 rods and would really put you back in the seat down low.  The 37mm vents as well as a heavy flywheel made for very docile low speed cruising in the dunes as well as good "on the hill" starts.

37mm motors are a lot of fun as drivers. In some ways, they seem crisper and faster than a 42mm motor. I'm sure in an all out drag race, the 42's would win hands down.

I remember being at Roger's shop in the late 1990's and there was a young kid working there that had a clean sedan with alloys, 2276, K8, Roger's heads and IDAs. Roger went somewhere and took the kid's car, and I was impressed with how crisp and snappy the motor sounded as Roger left the parking lot. When he came back he told me the secret was the 40mm vents. He said the kid wanted to go home and put 42mm's in it,  but Roger told him it would make a big hole in the power.

I've spent (wasted?) so many hours going back and forth with vents on the motors I've had in my cars, and I have to say, the 42's run "ok" but overall, I'd have to say the car always ran sweetest with 40mm's and locked up advance.

I ran my last 2165 (FK45) with 37mm's most of the time, and it was really sweet to cruise on freeway with, it just sort of floated along @ 75mph. But it was done at about 5800-6000 if I stomped it.
The 40mm would run thru 6800 in 2nd gear.

Rayburn's car seems to make good use of his 42mm venturies, as his car seems to pull like there's no tomorrow, idle on up to the orbit. Funny, by calculator... that motor could use a 46mm!

Santa, I want Dyno for Christmas. 

My only experiences with larger venturies has been with my current rig.  This is the only set of IDA's I've ever owned with a third progression hole.  I was never able to make a 37mm / f7-f2 combo work well with these carbs.  Finally, I tried some 40mm vents which solved most of the problem... the rest was cured by fattening the idle air holder to a 115.  Art Thraen recommended the f11 tubes and the 160/210 main stack.  It's all good!  Wait till Carlos sees you want Dyno for Christmas .... your in big trouble!!

[Jim Ratto]

Dyno Don C. had to razz me about this topic.... maybe we can debate for another year Don? 

If you take a peek in KS' new Cal Look book, check out jetting on Mahaffey's 198hp street motor (1970!)....120 airs?! 

Obviously "worked" in his Webers.

[Ohio Tom (DdK)]

yeah, motor sure do get "snappy" when you lock out the advance curve.
Seems to clean up the transition issues.... right now...LOL.
I really like to run hot street motors with locked out dist. They idle great....

[Jim Ratto]

yeah, motor sure do get "snappy" when you lock out the advance curve.
Seems to clean up the transition issues.... right now...LOL.
I really like to run hot street motors with locked out dist. They idle great....

No kidding Tom, one of the best things I've done was lock my MSD out. Car became tons crisper off idle, and go rid of a saggy spot off idle. I wired my 6A box so it is fired seperate from starter, to minimize kick back. Yes, and the ilde got that hard-edged, urgent beat to it too.... when you hear that, you know the motor is going to rip. Then that cracking bark when you open the throttles, you know there's more to come.

[Peter]

So have you found your answer Jim?