De-detuning a 2.4T / Stoddard Zenith 'sport' kit

[obrut]

In a recent discussion on Zenith's carb on the early S board, there was reference to a sport kit sold by Stoddards back in the day which purported to effectively remove the factory 'restrictions' on the T motors. It sounds similar to the factory sport kit that were often supplied with rally cars etc.


"I ran the Zeniths on my '70T back in the day. Stoddard sold a "sport kit" for 2.2Ts which was a set of custom machined 34mm venturis, appropriate jets, an E dist rotor (7000 red line), and foam Filtron filters. They recommended a twin pipe sport muffler, but I ran the stock single Leistritz on the street and open megaphones on the track. There were no other modifications recommended aside from venturis and jetting...stock enrichment, left wierd air balance tubes intact, etc. With short gears car ran like scalded rat. Stoddard claimed 35-40 hp which sounded like alot, but the stock venturis were 27mm which strangled the motor, and the way the car ran I tended to believe their claim. The kit was cheaper even then than a pair of Webers. The Zeniths were just fine...many time trial trophies including Parade. If you can find parts, they're OK. Hopefully Ed can help."


Does anyone know if a similar kit was available for the 2.4 litre T's? Are they availabe anywhere now (they're not listed on the Stoddard website).

If not, does anyone know have a recommendation for venturi and jet sizes to try and do something similar for a 2.4T?

I have recently picked up a super original 2.4T that runs like a champ but the thought of it being de-tuned by the factory irks somewhat...

[obrut]

Bump - and second question.

Based on the equivalent Weber setup, 30mm venturis would be about right.

Assuming I can find some 30mm Zenith venturis - what main jet size would suit?

[neilca]

Ryan,

I am running 32mm chokes in my 2.0L. It is no more than a street engine, but I run it on the track. No stumbles or flatspots. I will have to verify what main jet I am running. What we did to decide what jet to run was to take the percentage of area increased by the larger choke and increase the main jet the same percentage. We did this twice, I had changed choke sizes, and it worked both times as was verified on the dyno with an exhaust probe.

For the 2.4 I would go to 32 or 34mm chokes. I think it would handle that. When I build my 2.4 race engine I plan on running 38-40mm chokes eventually going to 46mm throttle bodies and EFI

The chokes I make myself. You cannot buy them.

The jets I get from this guy in Italy. Super guy to work with, I screwed up my order once and he fixed it, no charge.

PORSCHE 911 ZENITH TIN CARBURETOR MAIN JETS | eBay

I will check my main jets later today and post what I currently am running.

[neilca]

I verified my main jets are 160's

[obrut]

Thanks Neil, very helpful.

Sounds like 34's are the way go. I got 30mm from the Weber formula but note that the Stoddard kit used 34's in their kits for the 2.2's.

[Brant]

is your 2.4 stock with stock injection?

it kinda sounds like you have zeniths, but I only bring it up because you mention that your 2.4 is "super original"
if you did happen to have MFI, tuning is different than changing vents on a carb.

you really need an innovate or wide band sensor to look at your mixture across the range. Altitude, ambiant, and humidity will play into this. If you ever look at an amateur drag race event, most of the serious guys in the pits have very elaborate and very expensive "pro" weather stations. Jetting to the limits of performance require a lot of "weatherman" changes.

a dyno day can help you get started, or you can do it yourself if you have an innovate. If you push the jetting "limit" you will have to change them for every different track and every different weather condition (time of year, time of day)
you'll need a big supply of jets and parts if you want to find the absolute limit of performance

when you go bigger on venturi's you loose velocity rates. As you loose the velocity, you also loose the "foregiveness" of the combination. smaller vents will make any jet "acceptable" and mask flat spots. Big vents make everything more finicky. The more displacement you have the more you can help the foregiving-ness of the situation also. At some point there is not enough velocity left to perform at lower rpms. a really big venturi in a 40mm throttle body will stumble below 5,000 rpm (especially on a small bore motor). It will make more peak horsepower above 6500rpm but will not be a fun way to drive on the street.

I'm not detering you, I have big venturi's... but my car is a track only car and I geared it to never run below 5,000rpm. I'm actually running 34 vents in a 2.0 motor, with 180 main jets. (not a combination I would recommend to anyone that isn't willing to retune and rejet their car every single day depending on the weather changes between the morning and afternoon)

so like any other component in an engine its a compromise. You can tune the motor for 1 specific rpm or purpose but you give up somewhere else to make those gains.

kinda like the big cam arguement. A really big cam can look great at redline, but can suck coming out of the corners and actually be slower for anything other than redline.

the factory probably "tuned" the 2.2 zenith to actually make it a better driver rather than a stumbling and coughing street car with big venturi's

brant

[obrut]

Hi Brant,

The car in question is a Euro spec original 2.4T that is still running its original Zeniths with 27.5 Venturis. The car runs very well as is and I'm only thinking about a change because the thought of it being detuned by the factory annoys me and a small increase in Venturi and assoc'd main jet increase is easy to do and easy to reverse if needs be.

Not after building a race engine - already done that in something else...

[piggdekk]

When You change the venturi, do You need to change the auxiliary one as well?

[neilca]

No one size fits all. The main jet change will allow more fuel to make up for the increase in air.

[piggdekk]

Thanks.
making a new venturi on a lathe doesn't look too difficult. Much harder to reproduce the auxiliary one.
luca

[James Brown]

Contact pcar9119@yahoo.com He makes ventures fir zenith in any size you want. About $150/ set

[obrut]

Reviving on old thread: Does anyone know the stock main jet size for the Zenith's fitted to a 1973 Euro 2.4T?