Can I change the jet spread for better cruise??

Posted By: FlyFish

Can I change the jet spread for better cruise?? - 06/16/14 02:40 PM

I was jetted 88/100 at part throttle and the air/fuel ratio was good, but the WOT A/F ratio was too lean. I had to jet my primary up higher than normal because I didn't have jets larger than 100. When I changed it to 92/100 the car was too rich at part throttle, but ran great at WOT. So currently the carb runs like crap driving around town, but runs great at the drag strip when at WOT.

My question is, will it work the same at WOT if I reduce the primary jet by 4 numbers (making the cruise A/F ratio closer to optimal) and add 4 numbers to the secondary? I was thinking of buying a set of 104 jets to make it 88/104....any issues with this thought before I order the jets?

My car is mostly drag, some street with a 750dp on a single plan intake, running on e85.

Thanks in advance.

Posted By: DaveRS23

Re: Can I change the jet spread for better cruise?? - 06/16/14 03:35 PM

If you're running a power valve in the primaries, open up the PVCRs for the extra fuel at WOT. That is what they are there for.

Posted By: Bad340fish

Re: Can I change the jet spread for better cruise?? - 06/16/14 04:42 PM

Quote:

If you're running a power valve in the primaries, open up the PVCRs for the extra fuel at WOT. That is what they are there for.

Yep, thats what I did with mine and it has worked great.

Posted By: Cab_Burge

Re: Can I change the jet spread for better cruise?? - 06/16/14 05:51 PM

Quote:

If you're running a power valve in the primaries, open up the PVCRs for the extra fuel at WOT. That is what they are there for.

Posted By: mshred

Re: Can I change the jet spread for better cruise?? - 06/16/14 10:24 PM

Quote:

Quote:

If you're running a power valve in the primaries, open up the PVCRs for the extra fuel at WOT. That is what they are there for.

Yep, thats what I did with mine and it has worked great.

How to tell how big they need to be opened up?

I have the same problem with my carb

Posted By: Cab_Burge

Re: Can I change the jet spread for better cruise?? - 06/17/14 12:47 AM

Quote:

Quote:

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If you're running a power valve in the primaries, open up the PVCRs for the extra fuel at WOT. That is what they are there for.

Yep, thats what I did with mine and it has worked great.

How to tell how big they need to be opened up?

I have the same problem with my carb

If you have a wide ban on the car jet the part throttle down until you like it and then do the math on the diameter of the jet change size on the jets and then measure the Power Valve Restriction Channel(PVRC) inside diameter and open it up enough to make up the difference in same AFR ratio as the jet change made when you had the WOT AFR set at before changing the primary jet sizes

Posted By: DaveRS23

Re: Can I change the jet spread for better cruise?? - 06/17/14 01:09 AM

Quote:

Quote:

Quote:

If you're running a power valve in the primaries, open up the PVCRs for the extra fuel at WOT. That is what they are there for.

Yep, thats what I did with mine and it has worked great.

How to tell how big they need to be opened up?

I have the same problem with my carb

This really is wideband territory. But without a wideband, you can ball park it by using the formula in Emmanuel's Holley book. But you won't know how close you are to a good ratio, only that it drives okay or not.

You can just drill the PVCRs, they do not need to be tapped for jets. If you go too big, slender wires can be inserted to bring the flow down.

The Double Pumpers are good carbs for the track, but are calibrated very rich for the street.

Posted By: FlyFish

Re: Can I change the jet spread for better cruise?? - 06/17/14 03:13 AM

I have a wideband, and can drill the PVCR if needed, I was just curious if putting the larger jets in the rear would do the trick ( it sounds easier).

Posted By: Cab_Burge

Re: Can I change the jet spread for better cruise?? - 06/17/14 03:30 AM

Quote:

I have a wideband, and can drill the PVCR if needed, I was just curious if putting the larger jets in the rear would do the trick ( it sounds easier).

If your running a single plane intake that will fool the wideban but you will end up with a leaner AFR on the front cylinders at WOT, not a good thing when your on the edge of the tune up

If your using a dual plane intake that can happen also, fuel distribution can be a real pain in the rear to get correct on carbureted motors

Posted By: DaveRS23

Re: Can I change the jet spread for better cruise?? - 06/17/14 03:32 AM

Staggering the jetting can have a profound impact. Unless you have a way to measure where more fuel is needed, it would be best to jet it square. In fact, I run a power valve in my secondaries just so I can jet the primaries and the secondaries exactly the same. (along with the PVCRs) I don't want to risk a mistake calculating the jets for the secondaries with the power valve blocked.

Posted By: FlyFish

Re: Can I change the jet spread for better cruise?? - 06/17/14 02:36 PM

Gotcha, ok I'll get to work on the PVCR. Thanks guys!

Posted By: ajcasini

Re: Can I change the jet spread for better cruise?? - 06/17/14 02:42 PM

I would also use the 4window PV. Once you get larger than about 060ish on the pvcr the 2 windows just don't flow enough.

Posted By: Thumperdart

Re: Can I change the jet spread for better cruise?? - 06/17/14 06:55 PM

Quote:

Gotcha, ok I'll get to work on the PVCR. Thanks guys!

I look at jets as overall volume of fuel and bleeds as a way to fine tune the curve and until I got my bleeds in order, my jetting was screwed up for sure.

Plus, angle channels, properly located ifr`s and the emulsion circuit play a HUGE part in a nice clean fuel curve which I finally have and if I knew this back when I went 9.79, my sig would be quite a bit lower............

Posted By: Streetwize

Re: Can I change the jet spread for better cruise?? - 06/17/14 10:16 PM

All good advice, but sometimes upping the main jet size but raising the point where the PV comes in can do the trick too.

Posted By: Thumperdart

Re: Can I change the jet spread for better cruise?? - 06/17/14 10:48 PM

Quote:

All good advice, but sometimes upping the main jet size but raising the point where the PV comes in can do the trick too.

And I went from a 3.5(before I knew better)to a 5.5 4 window p/v and what a difference but I still say work the hi speed bleeds to fine tune wot.........

Posted By: FlyFish

Re: Can I change the jet spread for better cruise?? - 06/18/14 01:51 PM

In the past few weeks I have already dropped my HSAB down to a 0.028 (from 0.036), and that helped a lot. I got to thinking about it and I probably could just mix my e85 to be more like e75 and be able to jet down more. Currently the e85 pump closest to my house has been 92% ethanol. If I blend in more gas I should be able to run less jet, which might fix the issue....or maybe it wouldn't since the ratio would still be off....idk, just thinking out loud.

Posted By: Cab_Burge

Re: Can I change the jet spread for better cruise?? - 06/18/14 05:44 PM

I would be very careful on adding pump gas to the E85,I'm sure there are other additives in the E85 to help keep the alcholol and gasoline mix that could be foul up by not having the correct ratio of additives

Posted By: MR_P_BODY

Re: Can I change the jet spread for better cruise?? - 06/18/14 05:53 PM

Quote:

I would be very careful on adding pump gas to the E85,I'm sure there are other additives in the E85 to help keep the alcholol and gasoline mix that could be foul up by not having the correct ratio of additives

Pump regular is what they blend the E-98 with to get
the E-85

Posted By: Thumperdart

Re: Can I change the jet spread for better cruise?? - 06/18/14 05:54 PM

Quote:

In the past few weeks I have already dropped my HSAB down to a 0.028 (from 0.036), and that helped a lot. I got to thinking about it and I probably could just mix my e85 to be more like e75 and be able to jet down more. Currently the e85 pump closest to my house has been 92% ethanol. If I blend in more gas I should be able to run less jet, which might fix the issue....or maybe it wouldn't since the ratio would still be off....idk, just thinking out loud.

Ya, my 1050 had .037 hsb`s and was impossible to get it rich enuff at wot. I`m glad I didn`t jump on the E-85 band wagon and prefer a consistent fuel like the VP-101 unleaded which is legal even in your SUV and burns nice and clean to keep my O2 alive and way better than blending. Good luck............

Posted By: FlyFish

Re: Can I change the jet spread for better cruise?? - 06/18/14 06:54 PM

Quote:

I would be very careful on adding pump gas to the E85,I'm sure there are other additives in the E85 to help keep the alcholol and gasoline mix that could be foul up by not having the correct ratio of additives

I'll be careful, and thank you for your concern Cab. I'm a Chemist Monday-Friday, mixing chemicals is what I do.

Posted By: FlyFish

Re: Can I change the jet spread for better cruise?? - 06/18/14 07:04 PM

Quote:

Quote:

In the past few weeks I have already dropped my HSAB down to a 0.028 (from 0.036), and that helped a lot. I got to thinking about it and I probably could just mix my e85 to be more like e75 and be able to jet down more. Currently the e85 pump closest to my house has been 92% ethanol. If I blend in more gas I should be able to run less jet, which might fix the issue....or maybe it wouldn't since the ratio would still be off....idk, just thinking out loud.

Ya, my 1050 had .037 hsb`s and was impossible to get it rich enuff at wot. I`m glad I didn`t jump on the E-85 band wagon and prefer a consistent fuel like the VP-101 unleaded which is legal even in your SUV and burns nice and clean to keep my O2 alive and way better than blending. Good luck............

I bet you would like e85 Thumper. My car went from a best of 10.79 on pump gas to 10.54 on e85...and that was my 1st day running/tuning e85. Not to mention that it runs SOOO MUCH cooler. I bet in the fall I will be posting a 10.4x time slip.

I could just get a 55 gallon drum and not have to worry about the variability at the pump, but for now I'll adjust as needed.

Posted By: RobX4406

Re: Can I change the jet spread for better cruise?? - 06/18/14 07:32 PM

E85 shouldn't kill an O2 sensors with unleaded fuel as the gas component.

I'd run E85 except the closest station is 50 miles away.

Posted By: Blusmbl

Re: Can I change the jet spread for better cruise?? - 06/18/14 07:38 PM

Quote:

E85 shouldn't kill an O2 sensors with unleaded fuel as the gas component.

+1. Unless the E85 is blended with leaded fuel, there are no dangers to oxygen sensors.

Posted By: MR_P_BODY

Re: Can I change the jet spread for better cruise?? - 06/18/14 09:39 PM

Quote:

E85 shouldn't kill an O2 sensors with unleaded fuel as the gas component.

I'd run E85 except the closest station is 50 miles away.

Correct...it wont hurt them at all... we run O2 sensors in the
flex fuel cars

Posted By: Thumperdart

Re: Can I change the jet spread for better cruise?? - 06/18/14 10:25 PM

Quote:

Quote:

Quote:

In the past few weeks I have already dropped my HSAB down to a 0.028 (from 0.036), and that helped a lot. I got to thinking about it and I probably could just mix my e85 to be more like e75 and be able to jet down more. Currently the e85 pump closest to my house has been 92% ethanol. If I blend in more gas I should be able to run less jet, which might fix the issue....or maybe it wouldn't since the ratio would still be off....idk, just thinking out loud.

Ya, my 1050 had .037 hsb`s and was impossible to get it rich enuff at wot. I`m glad I didn`t jump on the E-85 band wagon and prefer a consistent fuel like the VP-101 unleaded which is legal even in your SUV and burns nice and clean to keep my O2 alive and way better than blending. Good luck............

I bet you would like e85 Thumper. My car went from a best of 10.79 on pump gas to 10.54 on e85...and that was my 1st day running/tuning e85. Not to mention that it runs SOOO MUCH cooler. I bet in the fall I will be posting a 10.4x time slip.

I could just get a 55 gallon drum and not have to worry about the variability at the pump, but for now I'll adjust as needed.

I`m good w/the 101 cos it`s close for now anyhow and E-85`s miles away....................