94 s dime

iTrader: (10)

ive got a bone stock longblock with th400 in my drag 4th gen and 3.90 gear.i also run vp 110 (consistency reasons) dont recall my timing at idle and until about 2400 and its locked out at 33*, just trying to get some more input from other people who have used these similar setups for a drag only setup. Carb is a quickfuel 750 has 40/40 squirters, power valve delete 76/76 jetting, have messed with air bleeds, and air fuel seems to be ok.the car ran 7.30's a few passes in the spring, and that was with 3.42 gear and 275/50 radials. now its on 28's with 3.90's and i cant seem to get any faster than a 7.60. i know weather may be a factor, but i dont believe its all of it. car traps about 90-91 most passes. i just figured id check timing to see if anyone saw anything crazy wrong. or had any suggestions to anythign you see.

onefast84

What rpm are you shifting at? That carb is limiting you. If it can handle 40 squirteds than it can handle a bigger carb. QF makes bigger main bodys. So look into that, but your baseplate will need to be big enough too. I am running 32* at 7.0 in the 1/8!

newschool72

iTrader: (12)

Is the bone stock long block an LS1 ? Im confused about the 110 octane for consistency . Too much octane is a killer of performance , if the engine doesn't need the cooler fuel. In almost all instances, you will perform better with the fuel that gets you closest to spark knock, with out spark knocking. Heat in the combustion chamber is power and higher octane fuel just cools the fire. If you are convinced you need the higher octane, I would crank the timing up about 4-5*s to maybe steal some of the HP back that you lost with the 110 fuel.

TXsilverado

iTrader: (18)

i always thought the purpose of higher octane was to run more timing? or to get away with more compression.

speedtigger

iTrader: (16)

A few things I can offer:

• Slicks are slower than radials. They have more roll resistance.
• Higher octane can slow you down in a low compression engine.
• Higher octane will typically need a little more timing than pump gas. Try the 100 octane unleaded race fuel.
• Race fuel can have different characteristic that will change your a/f ratio. So, you have to tune your engine on what you are going to race on.
• The weather should only be 1 or 2 tenths difference in the 1/8 on about 20 degrees temperature swing in a car like yours.
• Refine your timing with testing. I like to start at 26 and increase by 2 degrees every pass until you get the highest MPH.

speedtigger

iTrader: (16)

I am not sure what you are basing this on. He did not mention anything in his combo that would indicate this. In fact, we know very little about his combo other than: "stock longblock", "3.90 gear", "33 degrees timing" and "750 Quick Fuel".

We do not know the converter stall, camshaft, whether the carb is vacuum or mechanical secondary, shift points..... none of it.

newschool72

iTrader: (12)

In a way ,you are right. But the fuel isn't to run more compression or timing, it is required, if you go too high on compression or timing for the fuel you normally run. I think a lot of racers think more timing is a good thing, but in reality, the less timing your engine NEEDS the more efficient your combination is. Timing at 0* would be ideal, but it isn't possible, because the fuel needs a head start to make its flame front. The farther you start combustion ahead of TDC, the more the piston needs to fight against the expansion of combustion to reach TDC. This efficiency effect is easy to see in a well setup advance curve . This is why the advance is always less at max torque, because max torque is the peak efficiency of any engine. High octane fuel does one basic thing. It cools the fuel down to avoid too much temperature in the combustion chamber. Max effort , high compression engines need the cooling effect because the higher compression creates more heat ( heat is basically HP when in the combustion chamber) and needs the cooler fuel to keep the engine out of spark knock. If you throw high cooling value fuel in an engine that doesn't need to be cooled, you just waste the heat in the engine. Make sense?
This is also why E85 and alcohol have to have much larger jetting to make roughly the same HP as a gas engine. E85 and alcohol both have very low heat value per volume compared to gas, so it naturally takes more of it to make the same amount of heat ( remember, that is HP in the combustion chamber)

onefast84

um drag only!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

speedtigger

iTrader: (16)

My nephew only races his quad. That does not mean it needs a 1150 dominator.

onefast84

1150 dom, I didnt mean that big! More like an 850 cfm. I could take my properly tuned 825 off, and install you properly tuned 950, and my car would go faster.

speedtigger

iTrader: (16)

On your car, maybe. Ported heads, big cam, big converter etc. Throw too big of a carburetor on a near stock engine with not enough converter and you just turned it into a pig.

A lot of people think their engine needs a "950" because they see what they think are similar builds running a so called "950". What they don't know is that some 950s are actually more like 840 cfm. The Holley 950 HP is a good example. The venturis in the Holley 950 HP are the exact same size as the 750 HP. It just has a bigger base plate and profiled boosters. Most say it really flows are around 840 CFM. Now, the quick fuel 950 body is actually close to 950 cfm. It has larger venturis. Put that carb on too small of an engine at too low of an RPM and you will have all kinds of low speed metering problems. Instant PIG. Lousy 60', lousy drivability and weird a/f curves.

94 s dime

iTrader: (10)

100% stock motor, stock cam, 853 heads, never been apart. 4000 circle d stall, my air fuels are about 12.8~ at WOT, i typically shift at 6 grand. i bracket race every single weekend, consistency is key, i agree the 110 is to much for my combo, but switching back to pump gas in the same night, netted me about the same time, i could crank the timing up, 4* but being at 38 on a stock motor seems crazy to me lol.

94 s dime

iTrader: (10)

and i dont see the 750 being a limiting factor at all, stock motor should run with a 650. the squirter is just to get out of the hole . if my jetting was in the 90 are i would probably step up, but being square jetted in the mid 70's really sounds like the carb is about ideal for the setup.

newschool72

iTrader: (12)

It sounds to me like there may be something else in your combo holding you back to the point that you cant see the difference in the fuel octanes. In other words, something in your drive train is keeping your performance below the level of seeing the couple tenths difference I would think the octane would slow you down. Maybe an example of something that happened to me will explain it better. I had a restrictive cold air kit on my 72 Camaro. No matter what I did with my timing ( the reason I went to the track in the first place) my car performed the same, because I was hitting the air wall that was the max air flow the cold air kit would allow. Small timing changes are visible now that the engine is able to breath.
Is the rear end getting in a bind or do you have a bad fender rub with your new slicks, did something change in the ABS brakes that is causing brake drag ?

speedtigger

iTrader: (16)

I think your carb is the perfect choice for your combo. Personally, I would just play with the tune to see what you can tweak out of it. I know slicks last a whole lot longer and are cheaper in the long run on a race car, but radials are faster. You should use the D/A calculator to look up the air quality on the night you were running the 7.30s so and compare it to your last outing. Then you can at least have some insight on that.

http://www.dragtimes.com/da-density-...calculator.php

94 s dime

iTrader: (10)

car weighs in at 2800lb, lol no abs. no air cleaner, car is pretty straight forward, no rubbing on slicks anywhere, i agree a radial is faster, but not that much lol

94 s dime

iTrader: (10)

i was personally surprised the stock motor, with ebay headers, carb and stall would go that fast, but if it did it beginning of season , why cant it now. car ran in the 40's alllot! few dips into the thirtys. but regaurdless, its late september, if it was weather, i would think i would be close again weather wise

speedtigger

iTrader: (16)

It is probably just a combination of little things adding up to the total.

dogsballs

carb sounds right, think bigger tyre is killing it.

i'd step down to (or even borrow) a 255 radial, heck maybe even 235 if you got great suspension and track prep. don't think you have the hp, for 28" or slicks in general

i'd also put some valve-springs in it, rev it a fraction more, say 6400. maybe up convertor a fraction to 4200-4500.

these don't make a huge amount of hp, its a matter of getting them out the hole quick, and fractional gains to 60ft, multiple at end of track. hence small diameter radial, don't rob power and also keeps effective diff ratio.

94 s dime

iTrader: (10)

idk im about to just give up on it for the year, its pissing me off lol