Help me settle an argument

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UOP

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Ok, so I've been trying everything I can think of to improve my tune to pick up 2 tenths to get me in the 11's. One of my buddies (who isn't a racer) is convinced my carb is too small and just won't let up about it. To him there is no way a 650 dp is big enough for even my mild 360, and should easily be worth 2 tenths.

I don't think my carb is too small because it's not pulling a lot of vacuum at wot (all the way to redline). It only pulls about 1" of vacuum, so tell me, if my carb isn't a restriction, how could I pick up from moving to a bigger one? See this is where I think he's wrong, but I'm open to the thoughts from guys who know more than both of us. I'm not relying on old outdated calculators, but relying on hard data here. I'm sure one of the real racers here than help me here. I'd appreciate it.
 
I would bet, properly tuned, it would pick up et going up in 100 cfm steps all the way to a 950.

90 MPH 1/8 miles are good for really high 11's. Got to get it moving early, like mid 1.60 60' times.
 
UOP said:
Ok, so I've been trying everything I can think of to improve my tune to pick up 2 tenths to get me in the 11's. One of my buddies (who isn't a racer) is convinced my carb is too small and just won't let up about it. To him there is no way a 650 dp is big enough for even my mild 360, and should easily be worth 2 tenths.

I don't think my carb is too small because it's not pulling a lot of vacuum at wot (all the way to redline). It only pulls about 1" of vacuum, so tell me, if my carb isn't a restriction, how could I pick up from moving to a bigger one? See this is where I think he's wrong, but I'm open to the thoughts from guys who know more than both of us. I'm not relying on old outdated calculators, but relying on hard data here. I'm sure one of the real racers here than help me here. I'd appreciate it.
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I'm old and outdated, just not a calculator:D. A larger carb may give you a few HP at peak and maybe a few tenth's in mph, but not two tenths in et.
If your after just the et improvement you need to be more efficient which usually means 60' has to improve. Suspension, tires, lighter weight and the easiest, more gear.
 
Over the years, the numbers I found on 10-12 second 360's is that a 750 double pumper will be about a tenth faster than a 650 double pumper or 750 vacuum secondaty Holley "IF" they are tuned/optimized to the same level. Of course, there are a lot of little variables. But not 2 tenths worth unless the tune-up is off on one.

Bigger carbs could pick up a bit more, but can also be harder to find the tune-up. Double pumpers like more gear and converter (or 4 speed) but are harder to tune/coordinate the squirters and pump cams. But they can ET and MPH better than same sized vacuum if done right. Using a 750 DP, I can pull high 1.40 60' times running an IHRA Stock class 360 crate motor in the 11.20's at 116-117. Car weighs over 3,530 with unported heads and a hydraulic .474" cam. But I have a lot of gear, converter and cam duration. But there are other IHRA and NHRA class cars that do even better with similar combos.
 
IMO, it all ddepends on the combo, heads/cam/gear/stall whether a 750 will pick it up, I say try one if you can borrow it, or get a PF mainbody & drop it on, I think it'll run stronger ET/MPH with a PF MB over the 650 even on a not so wild 360, so your buddy might be onto something. I ran 12.5s tops with my mild 360 magnum with a 650dp, but i'm sure it would have run better with a 750dp. But remember i could only muster 5100 out of mine, if your shifting around 6K the 750 should work better.
 
Will it give you the extra tenths you need? Maybe. I am running a Holley 750 on my 360 block 408 stroker. I just put it on and took off my 800 cfm Edelbrock. The car is noticeably slower, even after adjusting it over the last few days. I believe your 650 is too small and it will be to your advantage to dump in some more fuel.
 
Mmmmm, interesting.

I'm usually not one to just throw money at a problem hoping it'll get fixed, so that's why I stood strong with my decision to keep the 650 dp. I remember reading an article somewhere talking about carb sizing and one of the things they did was talk about vacuum at WOT. So, when I hooked up a gauge to my junk and saw 1" vacuum I thought I was good.
 
Just a guess but i'm thinking your front to rear weight is probably 58/42. Are you hooking good on the leave?
 
With rear IRS,probably leaves soft.IRS don't usually like a pounding.
 
Yeah, it's a little heavy on the front, but it's not as bad as you'd think. I usually don't have a problem with traction, but it does squat hard on the launch. It's good for pretty consistent 1.68-1.69 60 ft times.
 
It's losing .30+ in ET the first 1/8 mile. That 60' and 90 mph should be in the low 7.60's at a minimum. Is it 87 or 90 MPH?

If it's running 87, then the times are pretty close to expected.
 
Nope, out of my group of friends I'm the only one who's trying to go racing.

I updated my sig to more recent bests.

Edit: I lost mph with my new combo. I just figured it was going from a 3.91 to 3.73 gear, plus having a much better 60 ft. With my old combo I was only able to best a 1.89 60 ft.

Just so nobody is left out, my old best was 7.89 @ 90
 
Well at this point anything that doesn't touch on a major component will probably only be baby steps to the 11's. Larger carb, any small weight reduction, a little timing advance, pumping the front tires up higher, synthetic fluids thruout and a nice cold/dry day might get you close. Good luck. I like the car, very unique combination.
 
Yeah I've done just about everything I can think of. Timing and jetting until it doesn't mph any more, air pressure changes, etc etc. I'm afraid I've milked it for all it's worth without starting to swap parts.
 
UOP said:
Mmmmm, interesting.

I'm usually not one to just throw money at a problem hoping it'll get fixed, so that's why I stood strong with my decision to keep the 650 dp. I remember reading an article somewhere talking about carb sizing and one of the things they did was talk about vacuum at WOT. So, when I hooked up a gauge to my junk and saw 1" vacuum I thought I was good.
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i think that any vacuum at WOT is too much. it just represents a restriction in the intake track. sort of like when you take a reading at idle the blades are closed and the restriction is those blades so you get a vacuum reading. at WOT it's the same concept only this time it the throttle bores that are the restriction. so if all that makes any sense try 750dp. i also think that those little motors would like more gear, something in the range of 4.10-4.30.
 
I used to run a 650 dp on my 360. I put a 750 Proform main body in it and it picked up 3 tenths and 3 MPH....no joke. If you have a 100 bucks to spend, I would put Proform main body in it. It only takes about 20 min to install too. I still use that same carb today on my 410 stroker...see sig for times.
 
flyfish said:
I used to run a 650 dp on my 360. I put a 750 Proform main body in it and it picked up 3 tenths and 3 MPH....no joke. If you have a 100 bucks to spend, I would put Proform main body in it. It only takes about 20 min to install too. I still use that same carb today on my 410 stroker...see sig for times.
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I like that idea too fly. Not sure he'll get the 3 tenths though. How much more cam and comp. did you have? I assume he has stock Magnum compression and his cam is .506 - 216/224*. Surely there would be some improvement though.
 
Does Pro Form make them bodies for a vacuum secondary?
 
UOP, if you are considering a proform main body, I may have one here. If you want to try it, I can send it to you and give it a whirl. Just cover the shipping.
 
OldmanRick said:
I like that idea too fly. Not sure he'll get the 3 tenths though. How much more cam and comp. did you have? I assume he has stock Magnum compression and his cam is .506 - 216/224*. Surely there would be some improvement though.
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My combo at the time was a 360, OOTB Eddy heads, 10.8:1 compression, and a MP 292/.509 cam. Probably a good chunk of the gain was going from a main body with a choke horn, to one without.
 
Well I guess I owe my buddy a beer and an apology, lol. Well, I was nice about it, so maybe just a beer.

I do know that my combination isn't optimized for the strip, but I was going for something that I could both take to the strip or run down the interstate for hundreds of miles. Attending Drag Week was a big influence for the parts I put into it.

After reading some of the responses last night I am interested in the proform main body. One thing I did do to my current carb is cut the air horn off, so I don't know if it will pick up enough to get me in the 11's, but if swapping main bodies (and tuning) will get me within a tenth or so that would be a great start.

Thanks for the input fellas.
 
Thanks to Rob I get to try a Proform mainbody to see what it does. I'm going to swap it onto my motor tomorrow and will hopefully have something to report next weekend after a visit to the track. :cheers:
 
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