five7kid

iTrader: (14)

Stick with me here.

I've been running a 750VS/4150-converted Holley on the 396 for just under 2 years. My best time to date at altitude was in April (see sig, DA was about 7000' that day)[Edit: Since I've changed my sig now, that old best time was 14.37]. I'm borrowing (with option to buy) a 650 DP to see how it works on my combo (the size Holley's charts & formulas say I should be running).

Granted, some of these differences may be due to VS vs. DP, but here's my last run, on June 28th, with the 750VS (TT run b/4 that very similar):

60'----2.288
330'---6.342
1/8----9.593
MPH---76.28
1000'--12.380
1/4----14.744
MPH----95.68
DA ~8900', ~10 mph tail wind.

(Note: That was with the Warlocks uncapped, 185x14 front tires. Since then I've put Dynomax 3"x16" bullets on the Warlock cap flanges - the Warlocks capped would typically cost me 2 tenths, and 205x15 front tires.)

My first run with the 650 at test & tune tonight, I realized after shifting to 3rd that I didn't have it floored all the way (those mechanical secondaries are a lot stiffer than the VS). The slip showed 14.622 @ 95.17 with about a 15 mph head wind, 60' was 2.242.

I put on a weaker return spring, and got in 3 more runs:

60'----2.255-----2.230-----2.246
330'---6.191-----6.166-----6.178
1/8----9.385-----9.357-----9.370
MPH----77.65-----77.55-----77.53
1000'--12.134----12.116----12.130
1/4----14.468----14.454----14.473
MPH----96.93-----96.82-----96.51
DA ~8700 (had a rain shower b/t 2nd & 3rd run), wind let up some for 3rd run. I also shifted 100 RPMs sooner on the 3rd run.

Okay, this isn't exactly apples-to-apples, and a "real" comparison would throw a 750 DP into the mix. But, I'm quite impressed with these results.

I think the guy who currently owns the 650 will have $200 more in his pocket the next time I see him.

Oh, did I mention I know where there's a 750VS converted to 4150 for sale?

Jester

I think you're seeing the large portion of the improvment from going to a DP, rather than from the change in cfm. I've always said that VS carbs have serious limitations, at any cfm.

IHI

iTrader: (1)

Call me crazy, but Fivekid, I'm sure you've read somewhere on this board my improvements by swapping carbs. For a 396 I would not even consider a 650...TOO SMALL!! You think it ran better, try at least a 750 or at a MINIMUM an 850cfm DP carb, then come back and tell me how bad the carb "theroy" is a joke. Again my 355 ran 14.1's with my 750VS-installed the Holley 830DP which new price in Jegs is only $330 and dropped straight down to 13.6-nobody can argue with me on those times and gains as they speak for themselves. Spend the extra $130 and get a NEW carb that'll make that baby do what you want-go faster!!!!

five7kid

iTrader: (14)

Did I mention the choke blade/shaft were removed from the 650?

The biggest difference seemed to be between 60' and 330'. That could be evidence of the DP vs. VS difference (and, IHI, you did change type as well, not just size). My point was the 650 didn't hurt power, as evidenced by the MPH.

I'm still mulling over the potential effects of altitude on carb size. My thinking is that is shouldn't make any difference - volume is volume, just jet for the oxygen content. But, there may be some effect with flow velocity that makes a smaller carb work a little better here than what would work best at sea level on the same engine. I don't know, haven't had enough opportunities to test at each condition, and haven't heard much discussion on the topic (who bops between sea level and 5800', anyway?).

I do know this: I talked to one racer last August who's running a '70 Nova with stock bore 454. The engine was built by a shop in Colorado Springs who said he was optimizing it for 6000 RPMs (the racer's choice for longevity) and this altitude. The builder chose a solid cam with specs very similar to mine (slightly more lift), ported the heads with velocity in mind, 1-7/8" primary headers, topped it with a Stealth & 1" spacer and, {drum roll, please} 4150 model 750DP with choke blade & shaft removed. He shifts at 6000 and runs 12.0's all day long. Run the Holley formula on that and even at 100% VE, you don't get an 800.

I certainly like the consistency it showed last night run-to-run. Haven't seen that ever with the VS or q-jet. I think I'll run this carb at least for the rest of the season (which only goes through next month, then they start a fall series), and if a 750 keeps calling me, I'll do the Proform main body. Total investment would be $310.

I keep thinking I want to go with a Comp solid cam with powerband to 6500 RPMs, Stealth, & higher stall converter. That comes to 750 CFM @ 100% VE per their formula. If I really go wild and bore it out to 4.250", 750 still works at real-world VE.

If someone has a 750 or 830 DP to loan me, I'll be more than happy to bolt it on and report the results...

IHI

iTrader: (1)

I have no idea what you guys in the sky have to deal with as far as altitude compensation on race day, but I know from personal experience at our track talking with the racers, bigger is better. We had a 950HP going around the track on different mills being a "test *****" for the bigger is better? theory and even when bolted on a 10.0:1 327 still picked it up .3 over what she was runnin with the 750DP. When we had the motor for the Pro truck I drive dynoed, it made the best torque curve and hp with a small 750 hp and actually lost 10hp on top when we bolted on a 850HP. the guys there running the dyno pointed to the screen to show the motor was only pulling a maximun 670cfm at 110%VE so they said the bigger carb would hurt it, which it did. Now, this is the first motor we've dynoed and got to see everything it does, BUT now that we've started getting the majority of the bugs out of the truck and it's finally gripping the track-went from 1.55 to 1.45 60's with a rear shock change, I want to bolt on the infamious 950HP and see personally the results on the track as I know what the dyno showed and Et/mph are my personal test area's not a computer print out. My buddy that runs the Malibui has a stock 454 short block-stock bore yet even!!! with 10.0:1 comp., stock iron heads, Victor Jr. intake, mild .620 lift solid cam, TH350/3500 stall and 4.11 gears running 11.6's with the 950HP in a 3500lb car. We just tuned a buddies new 454-was running a 396 with a 750VS, switched power valve to a 2.5 and I drilled the front squirter out .020 and that guy could not keep his face from splitting in half the smile was so wide, just think when he can afford the 950HP he wants. I will agree with you that going from the VS to a DP nets huge gains no matter the size 650 and higher...but hopefully somebody in the pits will have a minimun of a 850DP or the magical 950 for you to try, garuntee you'll be pleased!! Bigger is better on the track to a point, not trying to say you should bolt on a tunnel ram and twin Dominators, but all that formula hoopla and magizine articles in Car Craft, etc... are not geared at all out 1/4 mi. performance.
Back to the VS situation, round up an extra squirter, drill it out a minimum of .02 and try it, I really think that in itself will help alot since it will be delivering more fuel off the line and will actually mimic a DP until the secondaries open then you'll have the higher flowing cfm on the top end since it'll flow 750cfm instead of the 650. It's an easy experiment and it'll take all of 2 minutes to swap it back if the car does'nt like it.

five7kid

iTrader: (14)

Drag racing is truly an "area under the curve" thing, and improving lower RPM power/torque even at some sacrifice to peak #'s can yield substantial rewards.

In addition, consistency is paramount in bracket racing. The inconsistencies I've experienced are in 330' times, and to a lesser extent, 60' times. I'll gladly sacrifice a few tenths of best times to maintain a few hundredths variation run-to-run - especially as track/atmospheric conditions change. If a smaller than "peak-power-optimal" carb will produce consistency, I'll take it.

It took me almost a year to find someone with a DP they'd let me borrow. Most of the guys I know have 454+ CID or huffers. They're running Dominators, mostly. And, I am truly funds-limited, and have to take baby steps when making changes. So, $200 now and $110 later to get the desired results is easier than $330 now (and you left off the S&H, which I included). I've also heard good things about the Proform main body.

Side note: The difference in tuning between the way the other guy had it and what I've done is incredible. He was running a fairly healthy 350 in a '74 Camaro, slightly lightened, 4.10 gears, ran 13.5's (that's 12.5's in sea-level language). It experienced oil pump problems, chewed up the distributor gear, so he found a ready-to-run 454 to put in it last winter, topped with an 830. Now runs 12.6's. That's why the 650 was available, used for just one season. He had 74/77 jets, 3.5PV in it, which blackened my plugs immediately. I've got 68/74's in now, 6.5PV (also tried 8.5PV because of off-idle dead spot, must be something else because it didn't help), still a little rich in the primaries at least. I hope to play with it a little more tonight to see what I can do.

Oh, one last thing - switching back & forth between the 750VS & 650DP is complicated a little because he didn't give me the inlet nuts/screens, so I had to steal them from the 750.

IHI

iTrader: (1)

The better consistency like you was one of the first things I noticed when I installed the DP, and hell yes I'll take a slow consitent ride over a fast inconsistent one on race day, but there is something to be said for faster cars having a better chance at winning than the slow one since it's much easier to gauge distance at the big end because once you've caught them, it's all done you win-unless in the case of a double break and your further off the dail, but I'd still take the faster ride on race day.
I hear ya on the carb swaps being a PITA, seems either linkages are not right from your carb to your buddies, vaccum ports or lack there of always throws a nice wrench in the mix once it'sall bolted on. Well hey, good luck at the next race and I think you'll be that much better now the car is gonna be dailed tighter.

five7kid

iTrader: (14)

Thanks. The consistent guys all run DPs, it seems. Faster also lets the other guy redlight first, but that last run on 6/28 was a redlight win (for me) against a 12-sec car (waste of a perfectly good .006 light). Started to rain before the 2nd round, end of raceday.

This swap went very smoothly except for dropping one of the sintered filters (another post on that), and the return spring - which I didn't handle until much later than I should have. I just don't look forward to several repetitions of the process.

Damon

A DP is always gonna have a slight advantage over a VS, apples to apples just becuase the secondaries are going to get open FULLY the instant you mat the pedal. As long as you have it tuned well, it's gonna give you more "area under the curve" unless it's really badly oversized.

The VS carb is limited in how fast the secondaries can open. Regardless of how much air the engine wants it can only open at a certain rate without bogging- fuel flow through the secondary boosters can only "ramp up" at a certain rate- and that's really the limiting factor, much more so than how much airflow the engine can really take at any instant.

I think, personally, the QJet has an advantage in this area with it's pull-over enrichment tubes that act much like a secondary accelerator pump, but it's still not the equal of a truly dialed-in DP in drag racing (where it's gotta be EVERYTHING RIGHT NOW or it doesn't matter).

five7kid

iTrader: (14)

My only other experience with DPs dates back to 1974-1978, a tweaky home-built 302 (327 block, 283 crank), 12.5:1, LT1 solid cam & 2.02/1.60 angle plug heads, single-plane Torker intake. Aluminum Powerglide with stock 1200 RPM stall, 3.36 gears. The thing had no power below 2500 RPMs, so opening the secondaries at anything below that was instant death. It's made me gun-shy ever since, and influenced my decision to buy the 750VS 2 years ago. With what I've learned since, and my current configuration, no doubt I should have gone DP in '01.

The Holley replaced an Edelbrock q-jet whose AV's had a gritty feel to their movement out of the box, inconsistent as all get-out in opening. 0.2-.4 sec difference run-to-run was not uncommon.

novadude

Did that thing pull 3.0 60ft's? I'll bet chevettes could pull on you to 20 mph.

I have a serious dislike for the Holley Vaccum secondary set-up. I had a 1850-3 on a 327 w/ a PG and 3.08's. I played with numerous secondary springs, primary squirters, etc. I never could strike a balance between bog and feeling like the secondaries were not opening too late.

I replaced it with a rebuilt Q-jet (using a few "Damon" tweaks), and the car picked up everywhere. Going WOT off-idle feels better, and the car seems to pull harder on the top end.

I think a big problem of mine is the 1.82 1st, and the 3.08 rear. The Q-jet seems much more tolerant of a car that is undergeared.

five7kid

iTrader: (14)

I never took it to the track in that setup. On the street, I'd only do rolling starts. I put the engine in another '57 with a 3-speed stick & 3.55 gears, and took it to the track once (my racer was a motorcycle back then, but even so, they didn't give 60', or even reaction times back then). What I had to do with the stick was launch on the primaries only, right wheel spinning, and when the tire finally gripped I'd floor it. I was being sent overseas later that year, so I sold the car & engine before I had a chance to try to get it to work right (traction and a real clutch & tranny).

Took the '57 out again tonight. Running on DR's instead of the ET Drags (which usually costs me a little time), it pulled a 14.50. Still sorting out the "regular" street behavior (idle, off-idle, etc.), but the DP has a home. (Still thinking about that Proform body, though.)

five7kid

iTrader: (14)

Not to belabor the point, but this was this afternoon, semifinal round (7th run of the day, 2 time trials). DA ~9200', 5 mph headwind. I also jetted down slightly since T&T.

I'm right lane, in case you couldn't tell.

(Edit: Trying to get this to a managable size...)

five7kid

iTrader: (14)

And the 1st time trial this morning. Left lane for this run.

In between, things varied a little - on both ends...

(Edit: Man, this attaching thing is giving me fits tonight.)