Carb & Jets ...

[Panoz Paul]

Greetings ... I've entered the F.I. death spin & have been thinking HARD about the carb conversion ... A primary concern is the learning curve of jetting ... At a track day in Minnesota , i'll start at 50 degrees in the morning & finish at 80 w/ the track around 100 ...
Is there a continuous jetting / tweeking though the day ???
I've been going back & picking through old treads for a parts list & assembling the caveats ; any other help & insight would be great ...
Thanks / Paul W.

[Panoz Paul]

For Kel ; I thought I would provide some specs of the engine ... Ford Racing Crate / 340 hp ( M-6007-XEFMS ) Alum. heads W/ 1.94 in ; 1.54 ex ... Cam : M-6250-E303 W/ .498 lift ; .050 dur @ 220 w/ 1.6 ratio lifters that were changed to 1.7's ... Engine is all forged ... Is the Demon 650 the carb to go with & what / who's manifold ???

[eric1h]

I had Patrick at Pro-Systems build me a race carb specific to my motor build. price was EXTREMELY reasonable...

He shipped the carb I bolted it on, brought it to the dyno to tune, no jet changes needed. I have not touched it since i installed it and it has run flawlessly!

[NZGTRA17]

Originally Posted by Panoz Paul

For Kel ; I thought I would provide some specs of the engine ... Ford Racing Crate / 340 hp ( M-6007-XEFMS ) Alum. heads W/ 1.94 in ; 1.54 ex ... Cam : M-6250-E303 W/ .498 lift ; .050 dur @ 220 w/ 1.6 ratio lifters that were changed to 1.7's ... Engine is all forged ... Is the Demon 650 the carb to go with & what / who's manifold ???

Paul, your set up is not so far off what I ran initially with the 5.0 that made 340hp at the wheels and 335 tq.

Regards manifold, I think the best manifold for your current combo Paul is the Edelbrock RPM Air Gap. This will make great torque from down low and good hp up to 5500 - 6000rpm. This manifold would best suit the rest of your combination (heads and cam) which is targetted more at a power range of 2500 - 5500rpm.

If you think that you may push the engine rpm harder at some stage (as your forged engine is capable of running to 7000rpm+ should you choose) you could consider the Edelbrock Victor Junior manifold (builds more hp from 5500/6000 up) but you will lose some low end power and torque on the 5.0 and the car would most likely be slightly slower with this manifold at this stage. However should you upgrade in future (bigger heads/cam/compression for higher rpm) this manifold would give you some room to grow into power wise without spending more $$.

Carb wise Paul, I have used 650cfm Mighty Demons for some time and like them (great features for the price, many of which previously were only available with custom carbs). There is not much of a difference between a Mighty Demon and a Holley HP series carb. Either is a good choice. I purchased my current 650cfm Mighty Demon via E Bay for around USD$230 or 240. The person I purchased it off bought it new but couldnt get it to run properly on thier engine. Bolted straight on, changed the air bleeds/jets that they had screwed up and it has run great ever since.

Regards baseline jetting for a 650cfm carb for your combo at the track, I would start off with around 71's in the primaries and 84's in the secondaries. This is based off what we ended up running in my 5.0 (73's & 86's) but backed off a little as my engine had a bit more cam and bigger heads (185cc runners and 2.02 inlet valves). You need to do some plug chops to ensure you tailor the jetting to your setup.

If you havent tuned a carb in race conditions before Paul, I strongly recommend that you take the car and have it dynoed to get initial set up correct. This way you can bolt a detonation set to the engine and get timing and jetting optimised for the fuel you run on and ensure you have a safe tune for the engine. I always do this as I beleive it is the best way to get the job done. You can waste more time and money trying to get this right at the track and end up damaging your engine.

There after, I do change jets (but only a size or so) at the track to allow for changed altitude or atmospheric conditions.

Hope this helps, Kel.

[panozracing]

I have another 650 mighty demon f/s if you want one with an/ss braided fuel rail.

I have run my car at mid-ohio, barber, road atlanta, and all the florida tracks without changing the carb setup at all. I am currently running a 390cfm holley nascar restrictor carb. My engine builder set it up on his engine dyno and then came to the track to make sure it was running right for us. We havent touched it for years.

[boothkc]

Off the shelf Holley 650 +/- electric choke will work fine w/o any adjusting of jets. Once the engine is warmed up there isn't too much ambient temp effect as you don't race in the snow, right? We are maybe slightly rich, but that is safe and fine. We used a Edelbrock Performer and MSD distributor with 6ALN box (same as our GTS) to complete it. Works great....more power and ZERO head aches. I keep the Explorer motor rev limited to 5400 rpm and seems to be friend proof so far.

Highly recomend this. Took out 100#s of useless wires and FI crap too.

Kevin
GTS and GTRA

[NZGTRA17]

Originally Posted by boothkc

Off the shelf Holley 650 +/- electric choke will work fine w/o any adjusting of jets. Once the engine is warmed up there isn't too much ambient temp effect as you don't race in the snow, right? We are maybe slightly rich, but that is safe and fine. We used a Edelbrock Performer and MSD distributor with 6ALN box (same as our GTS) to complete it. Works great....more power and ZERO head aches. I keep the Explorer motor rev limited to 5400 rpm and seems to be friend proof so far.

Highly recomend this. Took out 100#s of useless wires and FI crap too.

Kevin
GTS and GTRA

Kevin, I'd just about guaruntee that you will be leaving power on the table with stock jetting. I have regularly picked up 10 - 20hp on the dyno by custom jetting and shooting for a particular air fuel ratio across the range. May not be an issue for some due what they are using the car for, but to me, 15hp for 4 hours work and $500 is pretty good value given what it costs to maintain our cars.

Likewise I am not sure what sort of temp variations you have when racing in the States Kevin, but in NZ it can vary between 50 - 85 degs F (6 Hour this year started out around 55F and climbed to around 70F) . With this sort of variance you notice it if you jet for the conditions. There is a very useful jetting guide in the GTS manual that I have started using as a guide.

Kel.

[boothkc]

Kel,
I guess I was looking at Paul's post with the idea of how much headache is a carb vs. FI. Seems he was wondering if you have to rejet alot for changing conditions and is does this offset the simplicity of the carb.

Agreed that in a racing engine there is good advantage to dyno tuning/jetting the engine etc. The GTS jetting guide is great. We have never rejetted our GTSs since the initial dyno tune and run 450hp in temps 50-110df w/o problems.

Assuming that he has a stock (ours made 230RW hp) Explorer GTRA it will run fine with an out of the box Holley and no changes for temps 60-110dF (assume sea level....if he's in Denver then rejet). Certainly, dyno run and rejet is a good idea, but not necessary (epecially right away). As HP goes up jetting is more important.

Kevin

[NZGTRA17]

Originally Posted by boothkc

Kel,
I guess I was looking at Paul's post with the idea of how much headache is a carb vs. FI. Seems he was wondering if you have to rejet alot for changing conditions and is does this offset the simplicity of the carb.

Agreed that in a racing engine there is good advantage to dyno tuning/jetting the engine etc. The GTS jetting guide is great. We have never rejetted our GTSs since the initial dyno tune and run 450hp in temps 50-110df w/o problems.

Assuming that he has a stock (ours made 230RW hp) Explorer GTRA it will run fine with an out of the box Holley and no changes for temps 60-110dF (assume sea level....if he's in Denver then rejet). Certainly, dyno run and rejet is a good idea, but not necessary (epecially right away). As HP goes up jetting is more important.

Kevin

No worries Kevin, I was more focussed on answering the carb/manifold question. Agree that you can get away with not changing jetting as ambient temp changes, paticularly if you dont want the hassle of chasing absolute best tune for the day.

All I notice is that the engine gets a little "lazy" (doesnt pull quite as cleanly or as hard) as temps increase significantly above or below tune temp. This will only affect times by tenths at most.

Kel.

[Panoz26]

my LS3 with the Mighty Demon 650, 78 primaries and 84 secondaries and large accelerator nozzles (I can look if you need/want to know those sizes) put down 376RWHP and 369 Tq on the Dynojet. A/F hung right @ 13.1.

Just an FYI..

[feqrags]

Another FI still on a gtra 5.0 stock. Tracks that i go to.. are 311',780', 1000' 4650',4999'. And all 300+ miles from home. Carb?? Jetting changes? only plans for the future are heads, cam. Also like I have read in other post - can't read current ecu with my reader. shop's snap-on, and dyno shops reader..thoughts on changing to obd 2..or stand all lone FI ..thanks Bill

[Panoz Paul]

Thanks To All ... I found a electrical glitch ; master switch conductors ... Also put the Bosch pump in the tank to eliminate the suck issue , since its a pump & will be profiding a independant circuit / switch to it for a back-up ... I've got to much in to FI up-grades to not try AGAIN ... Back to the track July 12th / BIR , MN ...
If it still craps , I'll be interested in the M.Demon 650 ... Thanks Again !!!

[feqrags]

Originally Posted by Panoz Paul

Thanks To All ... I found a electrical glitch ; master switch conductors ... Also put the Bosch pump in the tank to eliminate the suck issue , since its a pump & will be profiding a independant circuit / switch to it for a back-up ... I've got to much in to FI up-grades to not try AGAIN ... Back to the track July 12th / BIR , MN ...
If it still craps , I'll be interested in the M.Demon 650 ... Thanks Again !!!

Paul, glad you found the gremlins. What are the up dates? I just put in new in tank lines, and sump box under new foam. thanks Bill

[Panoz Paul]

I had John @ Panoz send me thier add-on electrical schematics ...
Found that our fuel pump & tail lights share the same electrical loom ... There is a triangular plug , under ECU , that goes out just in front of the passenger door ; un-plug it & the fuel pump quits , besides that , I've lost my tail / brake lights "power" reguardless ... Have now completely seperated these curcuits & re-built the fuse box that was so cobbeled up w/ jumpers I just shook my head ... Has any one else done this ??? Looking back , the the master switch glitch ( loose conductors ) was creating resistance that created the dreadful & progressive decline after 8 to 10 laps ... So ; when nut & bolting ; don't forget about your electricals ...
Life with a race car ... Thanks Guys ... Paul W.

[jmimac351]

What dictates the jetting offset between the primary and secondary jets? I've seen some offsets at 10 jets sizes, others smaller. Is it a function of something to do with the metering block for the particular carb or is it just what the engine needs at part vs WOT? Will altering the amount of offset versus a "factory" setting for a particular carb create issues? For instance, if you are trying to have the car run a little richer at WOT is it ok to just increase the secondary jetting without a corresponding increase in primary? What kind of beer is best?