FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: cjshaker on June 01, 2017, 10:18:01 AM
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I was wondering if there was a rule of thumb on making jet changes when you go from full exhaust to open headers? I know when removing an air cleaner assembly, you generally should jet up 2-4 sizes, depending. But I don't recall seeing or hearing anywhere how much of a change you'd need, if any, with going from a full exhaust to open headers. It's a 2 1/2" exhaust, so there is a fair amount of restriction there. Or is it not an issue with exhaust?
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Assuming no major restrictions with the air cleaner or the exhaust you shouldn't have to change much if at all.
Due to it being difficult to measure what restriction there may be, I'd say it depends on the current setup how much you need to change something. If I had a car like yours and was going to drag week, I think I'd buy an extra set of metering blocks.
Have one set up for the street and one for the strip with larger jets and PVCR's.
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I think it depends totally on the combination, and the restrictiveness of the exhaust. A wideband A/F is your friend here...
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There's no unleaded high octane (above 93) available locally, so I typically run a few gallons of 110LL to stay safe, and the lead doesn't play well with sensors. And I don't feel like grinding off the ceramic coating to weld in a bung on my headers.
I guess I'll have to experiment with a collector extension for a bung, back the timing off a couple degrees, run some basic 93 for a bit and see what happens. I wonder if a sensor would get an accurate reading if it were only placed in a short extension before the exit?
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I put a WB in my wagon this past winter. It only reads correctly after going down track. At idle or slow moving it reads way lean(not enough exhaust flow over it).
I put it in so I could see what it does with the 1850's on it and then when I get the 735's done I can see where the tune is at and jet it similarly.
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The wideband O2 sensors will run quite a while with leaded fuel, so not to worry there. Having them close to the exit of open headers will effect the reading significantly, though, unless you are at WOT. Maybe some long collector extensions, with the bung welded right up at the front, would work for track purposes. Mine seem to work at the track, upstream about 14" from the end of the collector.
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If you are going to put it much past the end of the header flange (collector end) I would use a heated sensor. For tuning the street car I have a bung located right past the flange in the collector extension. Also, I just run one with the laptop until I get the carb tuning where I want it, then put it back in the drawer. No need to run around with it all the time.
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I can put the sensor within an inch or so of the flange, and using a longer extension for an accurate reading wouldn't be a problem. Sounds like a good plan.
And yes, this is for track purposes only. I know my street tune is fine, but wasn't sure how much things would change by removing the exhaust for track duty. And Chris, I remember you mentioning removing them after you were done, which is my plan. No reason to keep them once I know for sure.
Larry, does yours have recording capability? I'd assume it isn't real easy trying to read the meter while rowing gears and keeping the car straight :) Can anyone recommend one that does have recording capabilities?
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This one datalogs; I think the LM-2 "basic" kit may require a hookup to a laptop during datalogging, but the complete kit has its own memory card that you can download the data from later. Its easy to hook up an RPM signal also, so that you are seeing how A/F changes with engine speed.
http://www.innovatemotorsports.com/products/lm2.php
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INNOVATEMOTORSPORTS is definitely the way to goo, and the newer improved Bosch 4.9 wide band lambda unit .
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Thanks for that info and link, Jay. I like the RPM logging capability to go along with the AF logging. Do you know if it can receive RPM data from an MSD unit? Maybe from the tach trigger or from a digital unit like the 7AL? If not, I'll contact Innovate and ask them.
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Pretty sure that it will receive the RPM data from the MSD.
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Logworks takes all sorts of inputs, even oil pressure, water temp, battery voltage, rpm, etc.
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I just wait til 8th mile mark when I stop shifting to see what it is reading. Likely not doing much right til then being at the near end of the collector(with no extension). That is when the motor starts pulling.
If you don't want to data log, use a go pro? If you mount it near the tach, you can watch it easily enough with a quick glance.
I know right now it is reading 11.9 pulling high gear through the lights.
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I think I'd rather data log. The GoPro will come in handy for several other things, but gathering some info about the RPMs would likely be useful also, and might show other issues such as tire slippage. Or it might even be useful for when I switch to a Soft-Lok in helping determine how much clutch slippage is happening.
Logworks takes all sorts of inputs, even oil pressure, water temp, battery voltage, rpm, etc.
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I'll check them out Drew. Like I mentioned above, I have considered getting into some data logging for future plans, where things like engine rpm and driveshaft rpm could be useful in sorting out clutch adjustments. I don't race with any regularity, so it comes down to my own wits and asking guys on here. I haven't looked into any multiple input loggers, but had planned on it sometime in the future.
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Logworks comes free with Innovate products :)
I run an MTX gauge but have data logging abilities. It's fun to play with, but don't get hung up on magic numbers. Some engines will happily cruise at 15 and some prefer 13.5 just use it for a constant. It's especially helpful to view the timing of events with a carburetor.
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Logworks comes free with Innovate products :)
I run an MTX gauge but have data logging abilities. It's fun to play with, but don't get hung up on magic numbers. Some engines will happily cruise at 15 and some prefer 13.5 just use it for a constant. It's especially helpful to view the timing of events with a carburetor.
Thanks, Drew. I didn't realize that was their software. I've been looking at it, and it seems pretty user friendly. I actually only want to use this to see what difference it makes when I run open headers. I know the carbs are jetted and adjusted good for street use, but it's hard to see if it's leaning out when the exhaust is off. By the time I run a half mile back to where I'm parked at, the plug reading gets skewed. And I don't have the car consistent enough to go by those numbers, although my MPH is fairly consistent, so I can use that.
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I dont know but i think its hard to read
plugs nowadays. If its the fuel or some
change in motor oils but i think there
is a black sticky mess on the plugs
always
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Thanks, Drew. I didn't realize that was their software.
I kinda got that feeling, thus why I mentioned it.
Just remember if WOT track effort is the only change you want to make (minus exhaust), it may benefit you to leave the jets alone and just change the PVCR's.
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I dont know but i think its hard to read
plugs nowadays. If its the fuel or some
change in motor oils but i think there
is a black sticky mess on the plugs
always
I'd agree, Heo. Fuels have changed drastically over the years.
Just remember if WOT track effort is the only change you want to make (minus exhaust), it may benefit you to leave the jets alone and just change the PVCR's.
I don't know what I would gain by doing that? To go back to the street exhaust, then I'd have to change them back (I probably shouldn't say it gets some WOT action on the street....so I won't ;D). Changing the jets would be easier. If I find out that it's also going a bit lean at WOT with the exhaust, then I could see doing it. That way I'd still keep my cruise characteristics. I should also mention that these are BJ/BK carbs and do not have replaceable PVCR's, as is, although I'm aware I can drill them out. And there are 2 carbs, so I still see the jets as being the easiest "quick change" for a day or 2 at the track, where it's either idling, or going WOT.
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I don't know a rule of thumb, but it's a big deal, in my opinion. 2-4 sizes is what I say for almost anything........ it's hard to quantify differences with one jet size......so 2-4 is the smallest easily distinguishable range.
The big deal is 2-1/2" pipes on your engine. You are really killing it there.
Do whatever you have to do to get 3" pipes under there. You might think it's not worth it because of the difficulty in fitment......it's worth it.
If you are going to run open headers, it's much better to err on the side of longer collectors rather than short or no collectors. You might actually run slower with open headers if you have no collector extensions and/or haven't changed the jetting.
JMO,
paulie
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I don't know what I would gain by doing that?
My point about adjusting pvcr's instead of jets was you could cruise in street trim during drag week (I assume your intended goal).
As long as you are keeping intake vacuum high enough to not trip the power valve you could keep smaller jets (64-66's or leaner still as dictated by the engine) for cruising on the mains.
For a WOT throttle burst the power valve would obviously open and so your larger power valve restrictions would come into play.
It'd be a way to not change anything for the duration of drag week and still cruise cleanly without fouling plugs or burning an excess of fuel. Really no downside to this other than not being able to go WOT on the street while cruising between tracks.... the massive benefit is not having to touch the carbs for the duration of the trip.
With stock BJ/BK carbs your PVCR should be .043
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My point about adjusting pvcr's instead of jets was you could cruise in street trim during drag week (I assume your intended goal).
As long as you are keeping intake vacuum high enough to not trip the power valve you could keep smaller jets (64-66's or leaner still as dictated by the engine) for cruising on the mains.
For a WOT throttle burst the power valve would obviously open and so your larger power valve restrictions would come into play.
It'd be a way to not change anything for the duration of drag week and still cruise cleanly without fouling plugs or burning an excess of fuel.
I am all in with Drew on this. Using a in car vacuum gauge is a must tool. Going down in PRI main jets and playing with the throttle pedal in all different load and cruising situation to find where the engine starts to surge
and com back up to in jet size to what the engine needs and all this while you stay above in vacuum where the Powervalve opens and even find out att what point in vacuum the power valve needs to open and have the vacuum advance adjusted to go off before that powervalve opening point. The rest is "simple" math calculation in what area size the PVCR needs to be to compensate for the smaller area PRI main jets and like Drew seas, clean plugs on cruising and you still have the fuel capability the engine needs on WOT performance.
Hope my language and spelling was understandably
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Tobbemek gets it :P (your language skills are fine)
With my own car which has a lesser engine than Doug's (447ci, 2x4, 242/252@.050 cam, bbm heads) I find I can't really go WOT on the street anyway, nor is there a need to.... a few seconds and I'm doing 80mph and this is a much heavier car than a Mustang.
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I get where you guys are coming from, and I'm not trying to be argumentative, but this car sees 95% street duty. And at the risk of being toasted, that's where it sees the majority of WOT driving (clean clear country roads only, and with me as the only passenger). I don't even remove the exhaust during Drag Week because I don't feel like removing a hot exhaust and reinstalling it every day. The only time it comes off, or will come off, is during the last day of Drag Week or during the FERR. At least with my current engine and set-up. And I'm not going to bother with an exhaust cut-out because it's just not worth it when you're running almost 4 seconds behind class leaders. It's a 12 flat car, at best, as is. Nope, just for fun and the occasional race weekend. I appreciate the suggestions though.
Edit: And Drew, I don't know that I'd say yours is a "lesser" engine. Other than the rocker system and cam, there's nothing fancy about my engine. Stock unported iron heads, stock 2x4 intake, stock carbs, stock stroke, and only slightly over stock bore.
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I used to have a full 3" exhaust on my '67 Cougar. That was over the axle and under the rear bumper. There was no downside at all that I could see. I just found an exhaust guy who would do it. It wasn't perfect. I brought some 180 degree 3" mandrel bends, let him cut them up, and weld them up.
Doug, exhaust is one of the very few win/win, "freebies", in engine combinations. Let that bitch breathe and she'll blow kisses at you, as you both hurtle towards death in a cacophony of noise, fear, and physics. Something like that anyway......
JMO,
paulie
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LOL, Paulie! Did your car have staggered shocks? It would be much easier with the standard shock set-up, but the staggered shocks makes it a bit more difficult. I know I could squeeze them through, but then I think it would be very difficult to remove when I wanted to. I can just barely get mine out as it is, with the rear axle in full drop mode.
I made my own exhaust with stainless mandrel bends, and in the future it will get a full 3" system, but for now, it is staying as is.
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This thing with PW and Pvcr along with PRI MJ size testing is a standard presidier for every carb set up combo drag week or not.
To really answer the question" jet size with open ore closed EXH " You have to test the combo" No one knew what your combo likes.
different headers like different jettings like merge collectors likes allot more in jets. and headers vs stock iron exmanif often takes smaller jets.
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LOL, Paulie! Did your car have staggered shocks? It would be much easier with the standard shock set-up, but the staggered shocks makes it a bit more difficult. I know I could squeeze them through, but then I think it would be very difficult to remove when I wanted to. I can just barely get mine out as it is, with the rear axle in full drop mode.
I made my own exhaust with stainless mandrel bends, and in the future it will get a full 3" system, but for now, it is staying as is.
You're right, Doug. My Cougar does not have staggered shocks. I didn't think about that.