40mm Carbs/ 36 to 32 ventures assoc parts Ques

[RoninLB]

I want max acceleration between 3.4 - 4.4k rpm.

so in order to try to get more air/gas velocity at 3.2-4.2k rpm I want to order a set of 32mm ventures.. don't know prices?
I figure that a smaller venturi w/smaller relative % to throttle valve will increase low end gas mix velocity at the expense of max airflow. The larger drop in atmosphere will increase atomization also.

now all I need is the correct E-tubes. The routine is the F-3. My orig tubes are F-11. I'll have to read the books for a good guess to fit my act..[ 2.7 E-cams]. F-3 is a leaner low end and F-8 is a richer throttle response. F-11 is "common usage", whatever that means.

I have 135, 140, and 145 main jets laying around. My orig mains are 140. I may need another size either higher or lower ? 140 run great w/36 venturis. It screams from 4.4-6.4k rpm.

I have 50, 55, and 60 idle jets laying around. My orig is 55, but it ran better on 60 w/36mm ven. I think I'm covered with these jets using 32mm venturis?

Then there is the booster venturi.. I would think I definitely need new ones. I'll soon find out.

I think I'm on the right track ?

any suggestions ?

[pjv911]

Ron wish I had more experience with carbs . But in basic theory your airflow will increase with smaller venturies giving better cylinder filling at the lower rpm range . I think a 2.7 with 8.5 CR and E cams is not capable of flowing enough volume for 36mm venturies.
I would stay with the 140 mains and see how it works with the 32mm venturies.
Its all R@D from here .

Kurt Williams

[A Quiet Boom]

Ron,

Just a thought, you list the car as a 2.7S. Does it indeed have the S cams? If so this could be part of the problem. I run 36mm venturis on a 3.0SC motor with Bursh headers, my power comes on around 2500 and continues to the redline. Have you played with timing?

Back in the day when I ws drag racing my local track had a test and tune night, some nights I would go out and do "timing" loops, adjusting the timing up or down for each run, I also did carb loops changing jets on each run. If you have a local dragstrip you could run the car and shift at the top of your target RPM, do two runs on each setup for a little more accuracy then make one change and repeat until you find the sweet spot. I should also point out that 3000 RPM is cruising speed in my car with a 911 trans and I had a huge improvement in part throttle drivability as well as acceleration by going to larger idle jets. My idle is a little dirty but the car really runs well in this configuration. I don't worry too much about the plugs since I'm running MSD ignition and once the car hits part throttle it's pretty clean.

[911pcars]

Rnn,
BA suggests 34mm venturis w/a 2.7. Many use that combo. Also, the tall secondary venturis help low speed air flow encourage fuel flow from the nozzle.

Sherwood

[RoninLB]

Some new info besides the routine..

I went thru the books again and didn't find exactly what I'm looking for except what to hit on for R&D. BA stated that the 34mm venturi is a compromise with his routinely noted 2.7, E-cams, 8.5RS, And 36mm heads. I haven't confirmed my stock heads but I think they are 36mm.

Anyway I found a venturi chart for the 40&45 DCOE. The author, David Vizard, states that the increase from 34 to 36mm on the 40's dropped the signal at the aux/secondary venturi by over 50%.. WOW
That's what I need, better atomization.

Vizard's info and the BA compromise of using the 34mm leads me to be scared to buy the 32's and take a shot with the 34's. Once I have the venturis dialed in the rest will be R&D. I have Vizards phone number and really like his approach to max out carbs so tomorrow I'll try to contact him.

My situation is that nobody else uses their 911's as a cross country go cart where it's more of a chess game with the HP than a race to cover distance. The added bs is that I'm packing the car right now for a quick blast to Utah, clocking a couple of thou mi around the 4 corners, and heading right home. My bud heard that it'll be quick and he said "I'll go". I know he can take the beating from hanging with him offshore.
thanks guys for helping me keep my head straight.

notice the cfm airflow difference with the 40's from 32 to 34 to 36.

[Steve@Rennsport]

Hi Ron:

Lots of opinions on this so all I can offer is mine. I've done a LOT of these over the years,....

With all due respect to David Vizard, he would appear to have very limited practical experience with 911's, and Bruce (a VERY cool guy) will always be conservative, not knowing the experience and details in every individual case.

34's are a great choice for a torquey, E-cammed 2.7. With the tall aux venturies (VERY tough to find now & expensive when you can), and proper jetting, you'll have all the throttle response you want and retain a usable RPM range.

[RoninLB]

Originally posted by Steve@Rennsport

34's are a great choice for a torquey, E-cammed 2.7. With the tall aux venturies (VERY tough to find now & expensive when you can), and proper jetting, you'll have all the throttle response you want and retain a usable RPM range.

wow.. thanks Steve.

done deal. I'm thru chasing my tail.

thx

[Steve@Rennsport]

You're most welcome,.....

Go for it, man. Tweak those things up and you'll be in fine shape.

[A Quiet Boom]

I have two of Vizard's books and have found them invaluable over the years. I think you're on the right track. Something got me wondering though, if the car possibly has 36mm ports and you were running 36mm venturis I would think the signal would be very weak. If you follow the rule of thumb that a 36mm is good for a 3.0 (seems to be in my case but then again Zenith's have taller boosters) the 2.7 is 10% smaller and 32.4mm venturis would be about right. 34mm might still be pushing it a bit especially if the goal is midrange over max HP.

[A Quiet Boom]

Oops I must have been typing as you two where posting, I'll concede to Steve who has much more 911 knowledge than I.

[RoninLB]

Originally posted by A Quiet Boom

I have two of Vizard's books and have found them invaluable over the years.

I think you're on the right track.

36mm ports and you were running 36mm venturis I would think the signal would be very weak.

32.4mm venturis would be about right. 34mm might still be pushing it a bit especially if the goal is midrange over max HP.

Vizard is exotic imo. I tracked him down at some high end East Coast teaching university. His "How To Build Horsepower" vol2 is miss titled. His Carb trip is based on maintaining atomization thru all the circuits. Then he accomplishes it all. My opinion/ I think that he builds a carb in league with $5-8k FI. His work becomes university text.. cool way to have a good time imo.

I'm going joy riding no matter how the carbs are at time of departure. Early May to mid June is the best for zig zagging from about 500mi west of the Miss. R. to the Pacific and the season is in motion. I really didn't want to do 500mi/at least at 5-9k ft with the 36's so they were history. I can't go wrong with hard info on the 34's. "I think you're on the right track."... ditto


"weak signal".. exactly. Jetting rich or lean never got to the point where it sounded sweet. The best it ever sounded was like a very low compression combustion. It sounded real good to everyone else and it screamed above the low 4k's right on thru in 4th gear... meanwhile I see potential.

"34mm might still be pushing it a bit especially if the goal is midrange over max HP".. exactly. That means bonus coupons may still be on the table. "to explore new worlds where no man has gone before". I'm definitely getting a set of 32's a bit later for happy birthday to me.. Life is good.

ps to all: in the quest for mid acceleration I tried 145 mains over real nice 140's and it did do a low noticable increase. It also dropped all my egt's 25-50deg, depending on conditions, under flat/straight/steady/for miles 5th gear 3.4-3.8k. I'm on my 3rd straight bottle Techron covering my carbon parts.

[304065]

Ron, do you have a jet gauge?

I have this '66 with Weber 40IDA's, I want to know what's in it.

[RoninLB]

Originally posted by john_cramer

Ron, do you have a jet gauge?

I have this '66 with Weber 40IDA's, I want to know what's in it.

no jet ga. I didn't see one around Pelican Parts also. I did buy some kind of Bosch contraption that has .1, .2, .3, thru 1.2 pins.
Bosch pn 000 009 986 0.

If you can get a quick eyeball on the main venturi size it'll give you some info on what to expect. My venturis have a number written on the throat.

[RoninLB]

Originally posted by john_cramer

I have this '66 with Weber 40IDA's, I want to know what's in it.

I'll buy 32mm venturis if you have and will be dumping them.

[RoninLB]

Originally posted by pjv911

"your airflow will increase with smaller venturies giving better cylinder filling at the lower rpm range"
----- Exactly.. and the resulting vac+ leads to the droplets being blown apart into smaller atomization... this is what this whole trip is all about. I think great entertainment will soon happen as I super jerk off with getting atomization from e-tubes

"I think a 2.7 with 8.5 CR and E cams is not capable of flowing enough volume for 36mm venturies."
------ That was my original thought. The original was 36 + 55idle. NG, It was detonating at mid and high sections of rpm no matter.. [and I'll confirm that w/you later]. Back to 55idles that detonated right up to 3.5turns of the idle screws. So I started the 60idles at 2 screw turns and tried all options and settled on 2.5 screw turns. It screamed above 4k. It was rich below that but it ran real good .. BUT it wasn't good enough for my act.

"I would stay with the 140 mains and see how it works with the 32mm venturies."
----- I just finished one tank of gas on the 34 venturis and have only tried 135's because I was planning on a decent ride and I was somewhat thoughtful of millage.. meaning if I could get another 100mi from a tank with little decrease in entertainment I'd do it. It was a guess install because I had 5days to leaving on the ride that didn't happen. And I was gonna use them after testing only 50 low key pky miles. Meanwhile the 135's are good enough to run now till I'm ready to test the others. One thing thou is that where the 3.4-4k rpm, 36+60's+2.5turns acceleration drop in EGT's was around 75-100degF the current settings drop almost nothing.. maybe 25degF. WHICH leaves open the option that your 140's thought is a big time possibility. If the 140's don't crash the EGT's the added sizing will translate into power. I Think. actually all before is explained "i think"
Meanwhile... I have the 140's already and I bought 130's for entertainment. I've so far been quite happy with the 135's. EGT's have increased 25-50degF and have become more stable in 3.8-4.2k range compared to 36 + 60's. Temps are now a very stable 1,325-1,360ish. CHT's didn't move anything I could notice.. that's nice.


"Its all R@D from here."
-------- a few hrs ago I confirmed I had a platform to really become entertained. If atomization is the game then that means that accelerator vol, e-tubes, and who know what else I'll find can be really tweaked.

Oh yeah.. the first sentence of this whole big thread was
[/B][/QUOTE] " I want max acceleration between 3.4-4.4k rpm "
so current acceleration is just about the same or maybe a little bit better. I haven't put enough mi so far to really tell. It's only a rough/good enough current adj. One thing for sure is that the engine is now more dialed-in in many areas for my act. I'll buy 32's later to see what happens. Right now 34's have enough options to be tried. And Maybe the 36's+ would be a nice tune before a track weekend, don't know yet. "Its allR&D from here"


God Bless America

[RoninLB]

Originally posted by Steve@Rennsport

34's are a great choice for a torquey, E-cammed 2.7. With the tall aux venturies (VERY tough to find now & expensive when you can), and proper jetting, you'll have all the throttle response you want and retain a usable RPM range.

Originally posted by Steve@Rennsport

Go for it, man. Tweak those things up and you'll be in fine shape.

I just met a Hot Date a few miles ago. It's kinda like that infactuation thing. It's hard to explain.. and hard being used loosely of course.

[RoninLB]

found out that accompanying the nicer egt's was a Monty slight gurgle at times from no-girgle at all when richer.

So. I would have to infer that the line is consistant with other engines with the same package. When I'm able to do the 4-Corners then I'll know how the current setting egt's handle the 100deg+ deserts. If they rise more than I want it's easy to lower them.