I was just curious how sensitive your carbs were in regards to jetting changes affecting a/f? I went from 70/86 (10.0a/f @WOT) to 70/82 (10.3 a/f @WOT) and the a/f went up .3 . Is that about normal? I was just curious. This is the first time I have tuned a car with a carb. Thanks,

Darren

 

How sensitive is your CSU carb jetting changes?

So no one with a CSU and a wideband has ever changed the jets???

 

How sensitive is your CSU carb jetting changes?

Not yet, have not been able to find out. Or maybe not able to remember the amount of change, just that it did change. Sorry can't help.

 

How sensitive is your CSU carb jetting changes?

I am going to pull 2 out of the front and 2 out of the rear next, or 68/80. That should lean out my cruise a/f a little to help with the fuel mileage and help lean out the overall WOT a/f. I am wanting to get the a/f into the 11's. I just thought that removing 4 from the rear would make a bigger change than 0.3 . If I go to the 68/80's and it is still rich then I'll just start taking out 2 at a time from the rear til I get it where I want it. One thing that did make me curious was I pulled my timing up from 18deg locked out total to 22deg before I changed the jets, and saw no difference on the a/f. I really couldnt tell much of a power difference either. I would have thought 4deg would have been noticable? I may pull it back down to 18 while I am doing the jetting changes. Or I could just buy a smaller blower pulley

 

How sensitive is your CSU carb jetting changes?

Read my opening remarks from this dyno session.

Although I am running a ton more boost, it did respond to jet changes.

https://www.theturboforums.com/forums/showthread.php?s=&threadid=31173&highlight=888

 

How sensitive is your CSU carb jetting changes?

Just curious but did your cruise a/f change with the jet changes?

 

How sensitive is your CSU carb jetting changes?

Brent- Thanks for the link. I did look at that in my search, but a lot of your changes were accompanied by a change in timing as well. So I couldnt get a feel on exactly what was going on. Plus I thought it would be interesting to see how other CSU carbs responded as well, to give us an idea of how much they can vary from carb to carb and engine combo.

William-If there was a difference in the cruise a/f, it was so small that I couldnt tell.

 

How sensitive is your CSU carb jetting changes?

Sorry I noticed that you just changed the rear jets. It would be interesting to see if you changed the front jets what effect that would have. I wonder if more air is flowing to the front of the carb as opposed to the rear. If this were the case the fronts should have more of an impact, at least that is what my novice carb mind would think. On Brents car the change in the front jets created more of difference in A/F than the rears.

 

How sensitive is your CSU carb jetting changes?

That's a good point, I didnt think of that. I wouldnt think that would be the case since my hat is 90deg to the carb, but I guess it is possible. I would think that would have more of an effect with the hat coming off of the front or rear of the carb, but anything is possible. Plus I am running the EV hat, so I hope the divider inside is taking care of that. I'll try the fronts when I get it out of the shop and the roll cage is finished. I am hoping to put it on a dyno this weekend. Cross your fingers!!! Anyone else have any jetting changes v/s a/f readings with a csu?

 

How sensitive is your CSU carb jetting changes?

Hi,

I don't have a CSU carb mine is a carb shop unit but I'm sure they both use similar mods and my data should prove useful...

Novi 2k blower using an 8"-3.5" pulley combo make's 11psi @ 6000. 69/82 jets,

At 2800 RPM rolling down the highway the A/F was 11.6

WOT A/F was low 12's with a slow creep into the high 12's at the top of 3rd...

I installed a 3.20 blower pulley = 14psi and changed the jets to 72/86

At 2800 RPM rolling down the highway the A/F was 10.8

WOT A/F was low 12's with a slow creep into the mid 12's at the top of 3rd...

I believe that when your using a blower the faster the impeller speed is the richer the cruise A/F will be... i.e. if I just ease into the throttle rolling down the highway the A/F get's richer as the RPM's increase... This problem seems to become worse as blower speed increases i.e. the smaller the blower pulley the richer the cruise RPM will be... I also believe that the slow creep issue in the top of 3rd gear is caused be the increased load of a high speed pass and the power blower is taking to drive...

I'm not sure how effectively you will be able to tune the cruise RPM if your impeller speed is high and massive amounts of air is being forced at the carb... I run a large mondo bypass valve and that thing is "screaming" with the 3.20 pulley rolling down the highway at 2800RPM's...

FWIW, When I had the turbo on the cruise A/F at 2800 was 12.9 with the 69/82 jets... With turbo the impeller is barely turning at cruse speed and the carb seems to have much better control of the A/F because of this... I also didn't have the 3rd gear high RPM leaning A/F creep... This issue could probably be fixed with a little tinkering as others have mentioned in previous threads...

Timing has little effect on A/F readings unless your doing something extreem like going from 0 advance to +40...


Well that's my 2 cent's...

Good luck!

 

How sensitive is your CSU carb jetting changes?

Yeah Dave you got a real good point with the blower cruise A/F being richer because it is blowing more airflow going past the boosters which in turn is pulling un-needed fuel. I can get a cruise A/F with my turbo of 13.8-14.0 but the minute that I hit the throttle, the A/F will fall to 9.8 range almost instantly. It falls so fast that I am getting a nagging hesitation/bog on the hit of any gear change at that.

It was as simple as when you had the turbo on, the A/F got leaner since not alot of airflow was going past the boosters and pulling in too much fuel.

Did you get the PT-88 installed yet?

 

How sensitive is your CSU carb jetting changes?

Thanks for the replies. I am running a Mondo bypass too. At idle you can barely feel any air coming out, and I have not heard it blow off once. But then, I am only spinning the blower 50k @ 7k rpm, and it has a max speed of 65k. I can rev it up while leaning over the motor and put my hand in front of it, and it will blow off more air when I let off of the throttle, but stil not enough to hear. Hell I can cap it off with my hand and the idle a/f or rpm will not change! Nothing compared to my friends t trim on his 347 car, his is always screaming. I also have a 5spd, and even with my big cam I can pull it down to around 2k rpm and cruise without it bucking. I cant wait to get it out ot the shop so I can pull some more jet out and see what it does. It did feel a little crisper with just the .3 change. And btw Brent, I only tested in on the way to the chassis shop, so I didnt have room to wind it out and try a WOT gear change to see if it helped out my bog too. I'll get back to ya on that one once I pull a little more fuel out. And thanks for the pics of the clutch quad

 

How sensitive is your CSU carb jetting changes?

Hi Brent,

I'm not going to install the 88 until after the WFC... The truck was running very consistant last time out with the blower and I don't want to monkey with a good thing before the big race (Pro Lightning is an open comp format)... Plus I want to see how fast i can go with the Novi before I make the switch to the 88... My former transmission is toast because appearently I paid good money for some idiot to build it... I have now found a new transmission guy that really seems to know his stuff and is a drag racer himself so hopefully this will be the last of my transmission problems for a while... I had a completly new C6 built this one is going to have the standard gearing, The other one had the low ratio gear set and I think that was hurting me a bit... I sent the converter back to be loosed up a little and this transmission has a brake so I should be able to build boost on the line and get much better launch than when I had the GT45 on...

I hope to have it back together by this weekend for some testing and if everything goes according to plan I should be solidly running in the 10's using the 3.20 pulley making 14 psi... after the WFC I will try out the 3" pulley to see how fast it will go with it and then it time to install the 88...

Sound be interesting!

TTYL,
Dave

 

How sensitive is your CSU carb jetting changes?

droptop, what pulley combination are you using? you have a 418ci motor with a YS correct?

TTYL,

 

How sensitive is your CSU carb jetting changes?

That's correct, it's a 418 with a ys. Here's a link with more details: https://www.theturboforums.com/forums/showthread.php?s=&postid=299966

I have a 6.87 crank pulley, and a 3.33 blower pulley. The ys has a step up ratio of 3.45:1, and I am turning the motor 7k right now. I can turn it 7500+, but I want to get it on the dyno and make a pull to 7500 and see what my power and torque curves look like. Hope to do that this weekend if the cage gets done in time. With these pullies I am turning the impeller 49.8k @7k rpm, and 53.3k @7500. I have been told the ys is close to it's peak effeciency at around 59k rpm, and vortech rates it at a max of 65k. So once I get back from Ocean City at the end of this month, I am going to put a 2.95 pulley on the blower and see how that works. I am wanting to stay around 15lbs since I run 93 octane in this car and no intercooler, and have the timing locked at 20deg total. The 2.95 will put the impeller at 56k @ 7k rpm, or 60k @ 7500 (if the belt doesnt slip). I will probably switch to an 8in crank pulley if I have trouble with belt slip, but initially it will be cheaper to just try the smaller blower pulley.

 

How sensitive is your CSU carb jetting changes?

That is your first mistake thinking this is a cheap sport and there is a cheap way to do anything. I can't look at the car without spending 100.00 bucks. I think I have to pay to get in my garage. It really is starting to suck.

 

How sensitive is your CSU carb jetting changes?

BTW, this is my first boosted motor. I have always ran nitrous. So if you have any input that you may think is common knowledge to blower users with a combo like mine, let me have it. I am still learning.

Thanks,

Darren

 

How sensitive is your CSU carb jetting changes?

You will have belt slip!!! After what I saw on the dyno with a coge belt it is amazing these things even turn. On a pull the belt was not even touching the tensioner, the belt was streaching so much there were nothing but waves on the slack side, it is amazing.

You are doing better then me yours is running, I am looking for tips from you.

 

How sensitive is your CSU carb jetting changes?

I know how you feel. You start to wonder when it will stop emptying your wallet. Believe me I know this isnt cheap, I went $7k over what I planned on spending to build my motor alone (granted and dart block and blower were most of that). I figure I'll pick up a used pulley somewhere when I get a chance, and if it doesnt work, resell it, my 3.33, and my 6.87 and buy an 8in setup. Cant fault me for trying to save a little $$$$

 

How sensitive is your CSU carb jetting changes?

Do you want a coge set up. I know where there is one for a vortech that would work very nice.