valley firearms

thanks Kalli. I am adding some info in case it may help you or others. I don't mean to steal this thread but help keep it alive. I am running into the situation that you did. I maxed out my idle air bleeds at .098 before I got stupid lean and couldn't compensate with the idle screws. I did this one numbered bit at a time. I ended up going back to the .089 where I'm mid 13 with 1 1/2 turns out. When I bring up the idle I hit a lean spot for a split second and go into the 12's and richer. I have not taken it out for a spin yet to test WOT. If I go below 12 while driving I'll reduce my primary jet size.

Urban, just curiosity, why go high 12's when you have mid 13's? I would think you would be losing hp by going richer.

kalli

I think it's going to take a lot longer to get it right when you styart getting your cruise right and then adjust for WOT. I'd rather start back from scratch with correct spread and WOT

You should. It's dead easy and a picture says mkore than a 1000 words. Whenever I have a A/F question I post the A/F graph (if possible with rpm). Otherwise I'd be talking for 3 pages. It might help patrick to get more info as well. we could see the rich and lean spots and how bad they are and if the fluctuation is ok

nah. that's ok. exactly what you want. If you measure behind the crossover it would be a waste of time to use 2 bungs. you always should measure as close as possible to the engine. collector is a perfect spot (or right behind it assuming you don't leak there through collector gasket)

Valley: I wanted to play around with it, but weather is so bad, i'll probably leave it for the weekend. Plan to do Shelby drop on weekend, so it's going to be a few fun days ;-)

urban_cowboy

Well, that is a very good question. From all that I read, with pump gas, maximum HP is general discovered around 12.5-13 which is 10-15% rich. With my motor, through tuning it for years and trying now three carburetors, my motor hates 15s, likes 13s, and screams with mid 12s AFR. I figure I can live with ok power if it means a little fuel economy and not fouling plugs while cruising, but I want to get into that mid to high 12s AFR when I want tire melting power. That is why I am shooting for 12.5-12.8 AFR at WOT. When I get it to that point, I will put it on a dyno and play with the WOT AFR and timing a bit to max it out, but I think it is going to be close at the point. FWIW, I can tell a big difference in torque and power between 12.5:1 and 14:1 at least in this car, but I do not have empirical data to back this up.

As for tuning, I know that .007 square inches of fuel delivery in the front and back was close to perfect AFR and powerwise at WOT. I figure, I can go on that and set the jetting up to make some runs and should be close within a jet or so. I think I will start with drilling out the PVCRs to .060 and run a 70 (.073) jet in the front with a 83 (.094) jet in the back. Unless I am way off, this should be just a bit richer that what I had before when I was just a tad lean at WOT (73 (.079) jet in front with .055 PVCR and 81 (.092) in the back). If I am understanding this correctly, I can take away some primary jetting to get the cruise where I want it (I was at 73 and am at 69 now) and can open up the PVCR ports to richen up the partial and WOT. Patrick says I may have to go to .065, but I want to start low and work my way up. Keeping the same spread is important, but that spread number changes based on the size of your PVCRs. With PVCRs at .055, that equates to a 10 jet difference. If you open the PVCRs up some, the spread increases. I think it is just a matter of keeping the total area of your fuel delivery ports the same front and back.

I called Innovative Motorsports yesterday about a question I had and need to update the firmware on my LM2. I will play with that later this week and try to hook in the rpm data too so I can post up some graphs. I am curious to see what they say too.


This is fun now that I understand what is what. I could have lived with my Holley 750 HP and could have lived with my Pro Systems 950 but neither were perfect. I am after max power when I hit the throttle but not gas soaking the driver, passenger, and spark plugs during cruise.

kalli

that's exactly it. if you figure that WOT is good and cruise is lean, it wouldn't stop me changing the spread and PVCR if it can't be helped with mixture screws etc.
looking forward to get some graphs, that should tell a nice story of what's happening there. I usually print them out and comment them with what i did (cruise, wot, ...) and what carb setup i was running

urban_cowboy

Well, I got my LM2 connected to my MSD box so it now reads rpms, upgraded the firmware, and did a calibration this past weekend. I am now read to make some graphs. Unfortunately, I am traveling for work, so I cannot play for another week or so. I will get back to y'all when I get some garage time again.

kalli

looking forward to that. rpm+AFR in the graph should tell a god story

valley firearms

Urban, have you had time to play yet?

valley firearms

67mustang302

I haven't payed attention to the last 2 pages of this thread, too much to read. :P

Anyway, I couldn't get mine tuned right, no matter what I did it rich spiked between 2-3k. Ended up going a tad lean and fried the head gasket between 3-4. No biggy since the gaskets I run are good but prone to failure with bad tunes.

Though it seems like the cam is primarily the culprit, so I'm having Ed Curtis at FTI design me one....he already said the profile he came up with for what I need is quite different than what I already have.

Hopefully it'll be back on the road in another few weeks.

kalli

sorry to hear about your head gaskets, custom grind will be nice. Heard a lot about their skills. should have done that myself the day I changed the cam