skinny z

While I had an 1/8 mile pass or two of 8.07 @ 85.14 that was two years ago. I've been struggling with compression and timing with the new heads and short block ever since but it seems like I may have a handle on it now.

New bests in ET: 12.64 and MPH: 107.65. 3650 lbs w/driver. Street suspension.

60' is still off from my best of 1.71 from a few years back. 1.85 is as good as I could get this time around. ET streets at 12 psi and pre-loaded air bags.
The WOT carb tune was way off too. Interestingly, in highway testing, AFRs were 12.7:1. At the track, AFRs at the stripe where mid 13's. When I opened the cutout in front of the muffler, AFR's went to mid 14's. (Tells you something about my muffler doesn't it?).
There's more in it for sure. If I can dial in the first 60' (there's at least a tenth there) and fatten up the fuel curve, I think 12.5x is very reachable. Should see 109 trap speed too.
I hope to be back in a couple of weeks with my carb kits and hope for better traction.

FRMULA88

Your AFR is way too lean at WOT.. opening the cutout leaned it more.. (less back pressure) Increase your carb jet sizing until you see mid 12 AFR at WOT.. based on where you are at I would go up 4 jet sizes watch MPH on your timeslips.. keep increasing jet until MPH stops improving. you will never hurt the engine running too rich at WOT... too lean is when damage happens.


btw your tire pressure way to low for a drag radial.
My baseline for setting my stiff sidewall slicks (ET Drag) is 20 psi and this nets me 1.4x 60' times.

A radial at 12 psi is doing more harm than good.. I would increase to 32 and drop it in 2 psi increments. until you get the best 60'.

You will see than even at 32 psi you will 60' the same or possibly better than at 12 psi.. I used to Run Nitto drag radials.. with my 383 SBC 1.6X 60'
they like more air pressure.

FRMULA88

Once you get the jetting optimzed for best MPH
you can concentrat on 60' times.. fine tune the air pressure and practice your foot braking to see what RPM your car likes to launch at.

finally you can optimize the governor in the trans. For a street strip car I find it better to leave the trans in "D" and let it shift on its own. It will be much more consistant than a shift kit which more often delays your shifts.. B&M makes a governor kit for the 700R4 trans that is very easy to use.. The governor only alters WOT shift points.. so every day is unaffected by this mod.

for your small block (based on your mods) you want the trans to shift at WOT between 5800-6000. I would not wind up any higher.. The real issue is the 700 trans is a wide ratio transmission, ( not the best trans for drag racing ) the RPM drop between the 1-2 shift is less than ideal. over-reving the 1-2 shift does more harm than good. Depending how serious you want to get a th350 or 400 are the better choice.. if you want OD a 200R4 is better than the 700. The 1-2-3 in 200R$ are same ratios as a TH350 and a 200 can be built to take tons of abuse.

skinny z

I'm aware of that. I though it was an interesting observation. It's the difference between the "street" tune and what's needed at the track that really surprised me. From an ideal 12.7:1 giving it a blast on the highway to the track result of about 13.5:1. That the AFR's went leaner still with the muffler bypassed confirmed what I've been blathering about for years. You have to have a free flowing exhaust and a muffler that flows about 350 cfm like my Flowmaster is a hinderance to both performance and fuel economy.

MT ET Streets...26 x 10.5 bias ply slick. Minimum recommended pressure is 12 psi. I've run them at 10 looking for traction and it helped but that may be getting dangerous.
I need new tires for sure as these, although seldom used and always stored indoors, are about 8 years old. I've thought about making the switch to a radial but have conflicting data regarding if they're suitable for a car like mine or I'm better off getting another bias ply slick.

skinny z

That's the plan. If I had my jet kit with me I would have moved up 4 jets on the secondary as a starting point. I have a data logger too by that was also left at home.
The foot braking is another story altogether. My 10" converter only lets me get to about 2000 rpm before it starts to creep. Leaving at 1500 is easier and I don't really see difference in how much the converter flashes between the two launch rpms. I do know my reaction times are different between the two though. Have to work on that.
As for the 700, it's here to stay until it blows up. I've experimented with shift points but I typically shift at 6500 for the 1-2 as it lands in the sweet spot for 2nd gear. I spin there too though. Around 6000 for 2-3. Next time out, once I have the tune optimized, I'll do some back to back to back runs shifting a little earlier. My cam, by all accounts, is making peak hp around 5600-5700+/-. The engine hardware will handle 7000 rpm all day long so I have head room for engine overspeed (not that I'm making any power there).

For what it's worth, it's a street car first so I'm compromised as to getting the most out of it strip-wise. As it is, I cross the stripe at about 5400. There's room there too but I'm not about to mess with the rear gears. It cruises very well on the highway and the 20+ mpg is great for the long distance tours (like the 2500 mile odyssey I have coming up next month).

mw66nova

iTrader: (13)

sweet! get the AFR dialed and i bet it runs 12.4 or better

skinny z

That would be beyond my expectations but you never know.
Here's an interesting testing anomaly that I discovered. Two weeks ago, I made a trip to the track on a blistering hot day. Probably well into the 90's and high humidity. The car was smoking hot after having to sit in rush hour traffic for an hour (although engine temps stabilized around the 195 mark (with a 160 stat no less). Fully heat soaked too.
I typically race at the 180 mark and as little heat soak as possible. First pass, the car ran out of steam at the 1/8 mile mark. Second pass was worse and I could see the AFRs top out past 17:1 before I lifted. Back to the pits and removing the air filter revealed a good deal of vapour coming out of the carb vent tubes. I figured boiling fuel and called it a day. My fuel pressure gauge was on the fuel rail so I couldn't observe actual pressures when racing. This latest trip, without any changes from the previous trip other than relocating the fuel pressure gauge to the cowl, I could see fuel pressure drop from 6 psi at idle to just less than 4 psi at half track. AFRs were about 14:1 at the stripe as I described. That day was not nearly as hot and the engine temps weren't unreasonable. Not sure what to make of that.
Specs are: Edelbrock 110 gph mechanical pump, 3/8 lines from tank to pump to carb.
Is the low fuel pressure casuing the lean AFR (the previous vapour issues notwithstanding)? I can't see boiling fuel being a problem that day but then again. as I stated before highway testing showed excellent (12:7) AFRs at WOT but then again that's not nearly as demanding as being at the track when WOT is held for 12 seconds as opposed to 5 or 6 seconds on the highway.
Am I at the limit of the fuel delivery system? Are the 3/8ths lines restricting the fuel flow to the pump? Filters are 100 micron between the tank and the pump and 40 micron between the pump and the carb.
I'll be making another trip in two weeks but am starting to suspect it's not the fuel tune but rather the fuel system that's the culprit.
Any thoughts anyone?

FRMULA88

fuel systems 101..

You want no less than 4 PSI with a carb during a WOT pass down the track.
As long as the fuel bowls are kept full fuel pressure is not the factor, rather fuel volume is more important.

A 110 GPH mechanical pump should be OK however 3/8 ( -6AN ) is on the smallish side. Ideally you want -8AN (1/2) from the tank to the pump.

You can still used -6 from the pump to the carb.

A return line may also be a good option for a street / strip car. if you plan to make over 400 HP one day.
are you using a regulator with that pump, my guess is not but at your power level a regulator may not be necessary.
still not a bad idea as this will keep fuel circulating and prevent vapor lock.

FRMULA88

if jetting up does not improve AFRS on the WOT pass.. I would increase the size of the fuel line from the tank to the pump... and also the filter size.. don't use a -6 filter with a -8 line.. this will be the bottleneck.

BTW 107 MPH is mid-low 12s provided you can 60'.. but it sound like you are too lean.. are
you using wide or narrow band O2 sensors?

when I played with TBI we only had narrow band... which left a lot of room for error.. I knew my fuel curve was too rich because of the MPH on the timeslips and reading the spark plugs.. I pulled out a bunch of fuel MPH picked up.. yet 02 read same at WOT .8 LOL

at the end of the day the limiting factor for me was the wide ratio TH7004 and the dreaded 1-2 shift.
but my 383 went 12.16 @ 111.42 despite it

86LG4Bird

iTrader: (1)

Congrats on the new best, skinny!
And as already mentioned, there's "opportunity" left Not just with correcting the AFR, but also the better TC mentioned in your other thread in the Carburetor section.
Please clarify what tires you're running. and what size. Sounded like bias ply ET Streets to me, but FRMULA88 is assuming ET Street Radials.
If bias ply, other factors at play may have led you to believe 12 psi was better, but it sounds low to me......unless they're an extremely big tire??
If ET Street Radials, ... I've never heard of anything over 24 psi working out very well with them, even on a 4100 lb car running 1.3X 60 times. But FRMULA is right on cautioning about low psi with radials; anything under about 18 psi with those ET Radials is only slowing you down

skinny z

Thanks for the props.
Here are a few specs: 355 w/ iron RHS Vortec heads. 9.8:1 SCR. 7.9:1 DCR. Cranking compression 185 psi.
Custom 274 HR cam.
Crower 1.6 ratio .050" offset trunion rockers. (Rocker arm geometry absolutely perfect...finally!)
RPM Air Gap.
BG VS 750 cfm carb.
MSD igniton.
Hedman mid-length headers with single 3" to a bypassed muffler.
700R4 with Trans Go stage 2 shift kit and 10" TCI converter.
D44 with 3.73s.
MT ET Streets bias ply slick 10.5" x 26"-16" (which actually measure 9" across the tread). Best results at 12 psi.
Stock style suspension with Sensa-Trac shocks/struts and air bags.
Sub frame connectors welded in.
Race weight 3650 with driver.
That's about it.

FRMULA88

You will not get the weight transfer needed to plant those ET streets and improve the 60' with sensa tracks and stock springs.

Ideally you want to; remove the front sway bar, use 90/10 front struts, and 50/50 rear shocks (Lakewood makes bolt in parts for drag racing) also front drag springs (Moroso, Eibach)

You could get by with your OEM rear springs.. I have not changed mine.. but may switch to rear drag springs in the near future.

another thing to try is an adjustable torque arm (Spohn, UMI?) this will be a much stronger unit than the sheet metal OEM part

skinny z

I've thought about that but it's something I'm not likely to do. This car is 95% street. Hell, at the end of the month I'm driving it across the country. When I upgrade my shocks next time around I'm more inclined to go for the Koni yellows which would probably be even worse for weight transfer compared to what I have now. There's a road course (and drag strip) 20 minutes from where I'm moving to so I'll be taking advantage of it next season for sure.
That said, what gets me is that it's been in the 1.7's many times before. The only real differences were a 3.27 gear rather than the 3.73 and a 26" x 10" McCreary dirt track tire. Didn't even have air bags to help with the pre-load. I'd like to know where that performance went. About the only thing I can figure is that A) the engine is stronger and making better low rpm torque, B) the increased torque to the rear tires due to the 15% increase in gear and C) the ET Streets are getting old and don't stick like the old McCrearys.
I have a UMI adjustable torque arm set up for the proper pinion angle. Lakewood (square tube) LCAs too.

86LG4Bird

iTrader: (1)

I think I understand what you're saying, skinny: It's not a 1/4 mile car, but it's just logical to use the track as a gauge of how it's performing.
Not disputing anything FRMULA is telling you; however, take the following info as justification that it's "OK" not to dwell too much on all that good "track" advice you're getting.
My daughter's car in my sig has completely stock suspension, including the ORIGINAL 1986 bushings everywhere. With ancient ET Drags, it was cutting 1.65 60's with the 100 shot on the stock 305 motor. This was on an un-prepped test n tune starting line. Traction wasn't an issue. Stock suspension was doing just fine. I'm posting this to validate your position that you don't really need to sweat all of this stuff if 1.6 and 1.7 60' times for your car will satisfy you.

Sorry if I missed it, but I didn't see you state anywhere that you're spinning at the line. Are you? Or is this a matter of the motor not coming "on song" as soon?

skinny z

I'm all about building performance and horsepower especially (not to mention some fuel economy ) and the track is the place to prove it all out. Not to mention it's a blast when you go faster each time.
I understand where Formula is coming from. If I were to build a drag race orientated suspension, put huge gears out back, put in a close ratio transmission and a high stall converter, I'd be 11's easily. As it is, I going through the traps at just slightly more than 5000 rpm. There's room there too. I'll be moving in a month and the local track will be 20 minutes from my door. I may build a purpose built car just to race. But that's later.
However, such is not the case right now but I do know the car will 60 better. Even if I get back to what I had before with the McCreay dirt tires I'd have a tenth there and that's theoreticaly 2/10s at the top end. That's 12.4x or thereabouts.
And yes, it's a case of spinning. At the launch and again on the 1-2 shift (this trans works very well which is a surpise to me considered I did the shift kit and upgrades myself!) It's not a lot but the car does veer slightly on the shift so something getting loose. Despite preloading the air bags and getting a better angle with the LCAs, it still tends to squat on the launch and unload the tires. It's way better than it was before the bags but there's room for improvement still. It doesn't help that car is lowered by 2 inches all around. It's only 44" to the top of the roof!
I'm suspicious of the tires however when they were on my friends 67 Chevelle running 12.4s, spinning didn't seem to be a problem for him (although his 60s were in the 1.8 range too) but that's apples to oranges with the different suspensions.
Yes, I'd be satisfied with a 1.71 which is my personal 60' best. If there's more, so much the better.
Still gotta work out this tune though. Interestingly, the 1/8 -1/4 mile conversion calculators show that my 1/8 and 1/4 mile times correlate perfectly. (8.01 to 12.65) I'm thinking I'm losing power before the 1/8 mile point so there's a lot to be gained other than just the top end charge.

Fast355

iTrader: (2)

I have news for you, the governor affects ALL shifts in a 700r4, not just part-throttle. Governor pressure overcomes TV pressure to cause an upshift. The weights and springs alter governor pressure in relation to output shaft RPM. TV cable links to the carburetor to sense both engine load and driver intent.

1gary

Skinny it good to see your getting to the bottom of this.Keep it coming.

skinny z

Thanks Gary.
There's more in it I'm certain. I think with a proper tune and good air, it's solidly 12.5s and traction permitting, 12.4s. Considering that prior to this it was loafing about in the 12.8 range and then with no work on fuel or timing, it clicks off several 12.7s and then a couple of 12.6s, gives me the hope to be optimistic.

FRMULA88

Ummmm... No but you can stick to your version if you want.. I never had issues with part throttle shift points after modifying the governor.

Fast355

iTrader: (2)

I can promise you that changing the governor weights and springs alter the part-throttle shift points, especially under moderate throttle. I had one setup that gave 1-2 @ 6,500, 2-3 @ 6,200 and the under the lightest throttle it would not shift 1-2 until 3,500 rpm. Changed the weights/springs more than enough times in a 700r4 to know this simple fact.

FRMULA88

The 700 is no different than the 350 or 400.. the governor controls WOT shift points.

On the 700 the vacuum modulator was replaced by the Throttle Valve cable (aka TV cable) but it's function is the same as the modulator on the 350 and 400 in that it controls line pressure and part throttle shift points and downshifts.


Having modified the governor on my own 700 I can attest that only the WOT shift points were altered... which is what you want on a drag car..

if the TV cable is adjusted it will change the part throttle shift points. but if you left it at the OEM setting those shift points will remain the same..

FRMULA88

I have forgotten more about the 700 than most people know.

You want to the change the WOT springs, not all of them.
This is where patience and attention to detail pay off.


I did this mod. at a track outing using the B&M kit...10 years ago.
I was able to get 5800 WOT shift points 1st thru 3rd which was plenty for my 383. Part throttle shifting was unaffected. would still shift into 4th at 40 MPH.. approx. 2000 RPM.. then hold steady at 1500 RPM after the upshift.

Just because you can't do it does not mean it can't be done.

Fast355

iTrader: (2)

As have I and both the governor and TV cable control part-throttle shift points. With my old TBI setup I had my governor setup to give me OD at 35 mph with 3.08 gears. It would quite litterally hold OD down to 1,000 rpm at light throttle. When I swapped top-ends and put on a set of vortecs and a larger cam, I adjusted the governor to give me increased WOT shift points. The best medium I could hit was shifts around 6,000 and OD at 45-50 mph. The lightest throttle part-throttle shifts increased from 1,600 rpm up to about 2,500 rpm. Actually very desireable with the cam/heads/intake I was running.

Fast355

iTrader: (2)

Just FYI....I am not the only one that has experienced this.

http://www.corvetteforum.com/forums/...-governor.html

http://chevytalk.org/fusionbb/showtopic.php?tid/101233/

https://www.thirdgen.org/forums/tran...s-springs.html

skinny z

I'll have to get into the shift points a little more in depth once I've dialed the tune in some.
The trans that I've put together has the basic mods. .500 boost valve, "Corvette" servo, modified valve body and separator plate. Trans Go Stage 2 shift kit. At one point I swapped out the governor from what the trans originally had for a Caprice to what my transmission guy said was for a Corvette. And to tell you the truth, I don't remember what I have now. What I can say, is that with the TV cable adjusted according to the book, part throttle shift points and WOT are too high. Beyond 6000 at WOT. I didn't record what the part throttle shifts were at but suffice it to say they're uncomfortably high. My fix was to alter the TV adjustment slightly so as to bring everything in line. It didn't take much. Maybe a couple of teeth on the ratchet portion of the cabling housing. Now I know that this isn't the way to alter shift points as it can cause transmission death however in discussions with Dana at Pro Built Automatics, he's concluded that the .500" boost valve has made up for any loss in operating pressures due to the misadjusted TV cable. Not sure one way or the other but "touch wood" this trans has been a trooper for the many seasons I've been beating the crap out of it.

In conclusion, between the two of you, what should I be looking for in a governor that will pull my shifts points down to less than 6000 at WOT while allowing the TV cable to be properly adjusted and maintaining a reasonable part throttle shift?

FRMULA88

From my personal experience I tuned my trans at the track for the WOT shift points. You will have play with governor weight and spring combo that gives you what you want. I got it on my 2nd or 3rd try. I don't remember the combination. I sold the 700 a few years ago and went to a 400 with 'brake and manual valve body because it is substantially more durable for the intended application.

I also adjusted the TV cable for part throttle shifts while street driving. The TV cable did not need much tinkering; it's quite simple concept more cable tension = higher line pressure pressure = higher shift point. (to a certain degree) At least this is the way I learned how to do it from the trans shop that re-built my 700 and I never had an issue with it.

You also need to make sure you have the correct throttle linkage.. to connect the TV cable.
Anything besides the OEM TBI or TPI will have the wrong geometry and adversely affect the function of the TV cable.

Holley #20-121 Kickdown Throttle Bracket for GM 200R4/TH-700R4 Transmission. Should be used.. hopefully it will work with your BG carb..

skinny z

I can't imagine swapping out governor weights and springs at the track. I like to tune but that doesn't appeal to me too much. It's something that I could with my close access to the highway though. Any part numbers in specific I should be looking for? Here's another question. Would swapping a governor assembly with a Corvette unit (light car) for one that was originally for a Caprice (heavier car) raise or lower my shift points. I imagine the lighter weights would spin out faster and cause the shift points to be sooner. Does that make sense?
As for the TV cable and correct geometry, I went out of my way a long time ago to ensure that that was spot on.The Holley bracket worked with the BG carb however there were a few modifications needed. All in all it fits and works exactly as intended.

FRMULA88

B&M part # 20248 .. Personally I took a governor from a donor trans and modified that one. I then replaced the stock unit in mine, that way I always had one with the OEM settings (in case I wanted to go back) and it took little space in my tool chest.

When I sold my 700 I included both governors.

Swapping the governor is not a big deal, the cover is on the driver's of the transmission case.. open the cover.. pull out the old one and push in the modified one.

I don't know what a stock governor from a vette or caprice will do, my guess is they will all shift at WOT below what you need and will have to be modified regardless.