Engine tuning questions

[benno440]

Hey guys,

Been tinkering around with my timing and carb tuning and have a feq questions/thoughts.

505 stroker
ported stealth heads
ported RPM intake
pro systems 1000cfm carb
MSD 6al, blaster 2, and pro billet dizzy

Set my initial at 20* with 34* total, started to get detonation and starter drag.
backed it off to 18* no more detonation but feels a little sluggish, have the 2 light blue springs in the advance ( NO VAC ADVANCE) so its all in around 2400rpm.

carb tuning i dont have a good enough vac gauge so i used the demon carb tuning book from 4secondsflat.

where you set your 2 primary corner screws around 2 turns out, and the secondaries at 1.5 out, then put your idle where you want it, then tap the pump arm if it gets better adjust to suit and worse adjust to suit, i have all 4 corners now on the idle i need and when tapping the pump arm the engine does not die or rev up so supposedly it is pretty close to being spot on.


but after all this when going for a drive it seems a bit sluggish and when cruising at low rpm then plant it it doesnt quite stumble or hiccup but it slugs down if that makes sense.

could this be more timing orientated?

I am not sure if you guys know much about pro systems carbs but they have no vauum ports in them and they are built specifically to your engine specs and then tested, jets etc do not need to be changed unless you are less than 1 turn in or 3 turns out on the 4 corner screws supposedly.

 

[bigmanjbmopar]

Racing only motor?

 

[mopar12372]

what your fuel pressure

 

[62 Dart Convertible]

I'd suggest install one of these - no more guess work. I'm ordering mine real soon -

http://www.ebay.com.au/itm/AEM-Air-Fuel-Meter-Wideband-UEGO-/180806759041?pt=AU_Car_Parts_Accessories&hash=item2a18ec3281

 

[Meep-Meep]

1000 CFM seems a bit excessive for a street cruiser even with 505 inches.

 

[cryplydog]

benno, I'm with MEEP on carb for street. you didn't say what cam specs are or a compression test but I also question the timing being all in at 2400. also, if all is right with jetting I wouldn't think primary idle mixture screws would have to be 2 turns out to idle. that kind of says you don't have enough signal to idle circuit. just a guess. it could be the fuel is going counterclockwise swirl through the jets! " had to say it" good luck.

 

[benno440]

it was a custom built carb for my engine, supposedly new carbs these days can handle more CFM, is what I am told by a few engine builders. that's all I know.

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Racing only motor?

No

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what your fuel pressure

7psi

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benno, I'm with MEEP on carb for street. you didn't say what cam specs are or a compression test but I also question the timing being all in at 2400. also, if all is right with jetting I wouldn't think primary idle mixture screws would have to be 2 turns out to idle. that kind of says you don't have enough signal to idle circuit. just a guess. it could be the fuel is going counterclockwise swirl through the jets! " had to say it" good luck.

250/252 " .50 cam 108 lobe.
10:1 compression
98 octane all the time

car runs amazingly, double the power it had when I had twin 600cfm's on it, idles better so much more pickup and power just seems to have this sluggishness now.

 

[lewtot184]

all those 1000cfm holley or holley clones that i've played with have the same throttle bores and venturi area as an 850dp. far from being too big for 505 inches.

 

[67 coronet]

is the secondary linkage adjustable on those carbs?could be set for progressive vs instant open and causing your problem.

 

[Meep-Meep]

all those 1000cfm holley or holley clones that i've played with have the same throttle bores and venturi area as an 850dp. far from being too big for 505 inches.

I'll buy the fact that an 850 is very reasonable for 505 inches, but 1000 CFM is 1000 CFM as far as I know. Is the 1000 CFM rated at a different pressure drop on the newer carb? Smoke and mirrors rating system? If his carb actually flows 1000 CFM measured the same way as older carbs it may be too big because as you know a carb that is too large will give a lean condition. My point was it's difficult to pick up fuel when the venturi is too big and that might explain the sluggishness. Best advice I can give is to try different carbs - size as well as design - and see what the engine likes. He also has a 108 LSA cam and by nature it should be sluggish until he gets the RPM up so he may very well be stuck with the results.

Benno, I'm sure I've said this before. Get that 108 LSA cam out of that engine and install a 114. If you want all hell to break loose right off idle then put in a custom grind 114 LSA cam. Then try to wipe the smile off your face when everything suddenly starts working, including the dual quad setup that was your first choice.

 

[lewtot184]

I'll buy the fact that an 850 is very reasonable for 505 inches, but 1000 CFM is 1000 CFM as far as I know. Is the 1000 CFM rated at a different pressure drop on the newer carb? Smoke and mirrors rating system? If his carb actually flows 1000 CFM measured the same way as older carbs it may be too big because as you know a carb that is too large will give a lean condition. My point was it's difficult to pick up fuel when the venturi is too big and that might explain the sluggishness. Best advice I can give is to try different carbs - size as well as design - and see what the engine likes. He also has a 108 LSA cam and by nature it should be sluggish until he gets the RPM up so he may very well be stuck with the results.

Benno, I'm sure I've said this before. Get that 108 LSA cam out of that engine and install a 114. If you want all hell to break loose right off idle then put in a custom grind 114 LSA cam. Then try to wipe the smile off your face when everything suddenly starts working, including the dual quad setup that was your first choice.

is the venturi too big on the 750 you run on your 440? if the venturi area of 1000 carb is 7.8" divided by 505 = 64.74 cuin's per sqin of venturi. 440 divided by 64.74 = 6.79. cfm ratings are marketing ploys. i don't drink the kool-aid.

 

[benno440]

guys i dont think it is actually 1000cfm,

heres the details of the carb
1000 holley HP main body
Adjustable air bleeds
Billet base plate
VENOM II Billet Metering blocks
Adjustable throttle response
Built in alternate calibrations
Electronically wet-flow calibrated
Road race floats
Clear sight plugs
Stainless plate screws
Custom sized needle and seats
Stepped boosters
True race fuel curve
Live-engine tested
Wet-flow dyno sheet

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is the secondary linkage adjustable on those carbs?could be set for progressive vs instant open and causing your problem.

it is currently setup so that half throttle down opens the 2 primaries then pther half opens the secondaries, thats progressive isnt it? i believe it is adjustable yes

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I'll buy the fact that an 850 is very reasonable for 505 inches, but 1000 CFM is 1000 CFM as far as I know. Is the 1000 CFM rated at a different pressure drop on the newer carb? Smoke and mirrors rating system? If his carb actually flows 1000 CFM measured the same way as older carbs it may be too big because as you know a carb that is too large will give a lean condition. My point was it's difficult to pick up fuel when the venturi is too big and that might explain the sluggishness. Best advice I can give is to try different carbs - size as well as design - and see what the engine likes. He also has a 108 LSA cam and by nature it should be sluggish until he gets the RPM up so he may very well be stuck with the results.

Benno, I'm sure I've said this before. Get that 108 LSA cam out of that engine and install a 114. If you want all hell to break loose right off idle then put in a custom grind 114 LSA cam. Then try to wipe the smile off your face when everything suddenly starts working, including the dual quad setup that was your first choice.

yeh you have mate and i appreciate it, dont have the cash at the moment so have to work with what i got, just trying to make sure i have tuned it as well as i can for what i have. could my advance springs have anything to do witht the sluggishness as this has only come on since i dropped the initial slightly

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guys i dont think it is actually 1000cfm,

heres the details of the carb
1000 holley HP main body
Adjustable air bleeds
Billet base plate
VENOM II Billet Metering blocks
Adjustable throttle response
Built in alternate calibrations
Electronically wet-flow calibrated
Road race floats
Clear sight plugs
Stainless plate screws
Custom sized needle and seats
Stepped boosters
True race fuel curve
Live-engine tested
Wet-flow dyno sheet

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it is currently setup so that half throttle down opens the 2 primaries then pther half opens the secondaries, thats progressive isnt it? i believe it is adjustable yes

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yeh you have mate and i appreciate it, dont have the cash at the moment so have to work with what i got, just trying to make sure i have tuned it as well as i can for what i have. could my advance springs have anything to do witht the sluggishness as this has only come on since i dropped the initial slightly

Just had another look as my carb has clear sight glass for the float levels and on these carbs i have been told that the float level should be about 25% up the glass. i have set it before but now i cannot see the level again as it must be too low, maybe this has something to do with it as well

 

[lewtot184]

those carbs are around 900cfm but the venturi area is only around 7.8sqin's, definitely not big for 500+ inches. last summer i worked with a friend who has a 500" olds, big hydraulic roller cam and a 1000cfm "pro" shop somebody carb. we did some recalibrating on it and made some significant gains in drivability with no power losses. i don't think it's possible for these carb shops to do a 100% calibration on these carbs. there's just too many variables. i live in central indiana and the air temps can go from zero to 100f during the year and that doesn't include humiditys from 40%-95%. in my opinion everything has to be tinkered with to optimize it.

having tight LSA on long duration cams is common. keeps the intake valve from closing way late. the 500" olds has real vacuum problems because of the duration and tight lsa. this really can mess a carb up especially if there's automatic trans.

last note; the engine i put together this spring is a 440, alum heads, 9.75:1 compression, intake valve closes about 78 degrees ABDC, aggressive centrifugal advance (18 degrees initial, 35 degrees total with a vacuum advance) and has never given a hint of detonation with 93 octane. drives very nicely.

 

[benno440]

yeh well here can get from -1* c to 40* c, 20%-80% humidity through the year.

guess i will have to deal with it for now, still fun to drive

 

[383man]

Only thing I will add is I see alot of guys running the 950 to 1050 HP and Dominator carbs on 500 plus street engines. Myself I run a basically stock 850 DP (just jetted and drilled pump nozzle's) on my 493 and my solid cam is 264 & 270 @ .050 on a 110 LSA. I have it in the eng on a 106 ICL and I run 37 total all in by 1800 rpm and it idles at about 24 initial. I do use the basic EZ heads and no vacum advance. My driveability is great and it has no ping at all at any rpm. I would love to try a bigger carb as I feel very sure it would be faster but I will admit the driveability is very nice with the 850 DP and dont know if the driveability would be as good with more carb but it may. I agree that the carb you run will need fine tuning to your eng no matter who set it up for you. Good luck , Ron

 

[Xp29h]

I don't have the same motor by any means but with pro billet and Msd, I had to increase dizzy springs and bring initial timing up to 24 degrees to get rid of the sluggishness. I found it much better. I tried going back an just got worse.

Also I'm a fan of the 850 dp too!