raynman1969 wrote: ↑Sun Apr 01, 2018 1:00 pm
On the dyno it showed 1.8 inches of vacuum at wot. BLP 950 carb. 421 sbc afr 220 heads cnc super victor. Does this mean thecarb is too small or maybe it didn’t flow 950.
It could mean a numbe of things including the fact that the gauge is wrong. What are you trying to do with the engine? Do you need to make more power? Can you afford a larger carb or are you just asking questions? There are other 4150 flange carbs that flow more air if that is what you need but there probably isn't anything wrong with your existing setup for a street/strip type of combination.
Go over to a forum where NHRA guys hang out and ask them what the intake vacuum is on a stock eliminator car going thru the traps. Some of those guys run really fast with small carbs. Without knowing what your goals are for the engine there isn't any way anyone can provide you with an answer.
raynman1969 wrote: ↑Sun Apr 01, 2018 1:00 pm
On the dyno it showed 1.8 inches of vacuum at wot. BLP 950 carb. 421 sbc afr 220 heads cnc super victor. Does this mean thecarb is too small or maybe it didn’t flow 950.
It could mean a numbe of things including the fact that the gauge is wrong. What are you trying to do with the engine? Do you need to make more power? Can you afford a larger carb or are you just asking questions? There are other 4150 flange carbs that flow more air if that is what you need but there probably isn't anything wrong with your existing setup for a street/strip type of combination.
Go over to a forum where NHRA guys hang out and ask them what the intake vacuum is on a stock eliminator car going thru the traps. Some of those guys run really fast with small carbs. Without knowing what your goals are for the engine there isn't any way anyone can provide you with an answer.
Big difference between Stock/Super Stock and a street car or even a bracket car.
The OP needs to figure out what he wants first. And then move accordingly. If he doesn't want power left on the table, then he needs a different carb.
I have a 514 inch big block Mopar that makes around 900 hp on the dyno. This is an EFI engine so I have a MAP sensor in the intake and a barometer sensor on the ECU. At WOT the MAP sensor shows some pressure drop across the throttle body. The throttle body is 2200 cfm according to the mfg. Would a bigger throttle body make more power, maybe. Is it worth paying $1000 for a few hp, maybe. Am I going to put a bigger throttle body on my engine, nope. In my case I really don't care if it would make 915 hp with a 3000 cfm throttle body.
There are no answers to these questions unless there are more details. If the OP has unlimited funds then spend freely and report back what you find. If it is just a bracket car and it already is fast enough and the kids don't have any shoes then buy the kids shoes rather than spending the paycheck on a new carb.
This for a street/strip car and it made very good HP but when my engine builder said that the carb maybe be to small that is why i posted this question. If we get the vacuum down to .8 or 1.0 what will happen to the performance? Does is gain 4-5 horse or maybe it will make power in the upper rpm range not sure.
I am not looking to wring every hp from this engine but i want it to run good also and if this isnt right i would like to correct it. Maybe I am making a mountain out of a mole hill but that's why i posted on here to get different opinions.
If the gauge is accurate then sure, you could pick up a little bit of top end power by using a less restrictive carb. But the gains are not going to be huge and it could cost you a fair amount of money to get it sorted out. The easiest thing is if a buddy of yours has a big 4150 carb that you can bolt on and try. I have a Quick Fuel 4150 that is rated at 1050 cfm that I use on big engines when we're trying to make some extra power on the dyno. I run it on my 470 inch big block and it makes around 720 hp.
So if you had a buddy who had a carb like that then it would be easy to bolt it on and see if it makes more power. Just because it makes more power on the dyno doesn't mean it would go down the track faster though. Going down the track faster with a bigger carb is another can of worms to sort out.
Theoretically, an engine's power is proportional to the peak manifold vacuum. i.e., if it makes 500 hp with a carb producing 2.0" Hg, switching to one giving 1.0" will at STP conditions give 28.92/27.92 = 1.0358 or 3.6% more power.
It will gain a bit more power than just the theoretical power gain suggested by
the change in pressure drop. Why? because a engine consumes some power to pump the air in.
Make the intake less restrictive and the engine does not need to work as hard to pump it own air in. Thus more power at the crank ready to do work. "horsepower".
It can pick up as much as 25hp. Double the carb size. use 2carbs or one BIG 1350cfm dominator.
How much fast that will translate to depends on the car combo.
The more aggressive you gear the car and the higher you then buzz it thru the traps
above and beyond the peak HP rpm point the more difference it will make
in 1/4 mile ET and MPH gain.
raynman1969 wrote: ↑Sun Apr 01, 2018 1:00 pm
On the dyno it showed 1.8 inches of vacuum at wot. BLP 950 carb. 421 sbc afr 220 heads cnc super victor. Does this mean thecarb is too small or maybe it didn’t flow 950.
Did you have some type of flow meter to measure incoming air volume to the carb?
We use a flow meter that looks like a large velocity stack to check incoming air volume to help in choosing carbs size.
if the engine can't pull 950 you may need smaller or as mentioned a different carb for comparison. Again if there is a restriction you must determine that 1st and the only way is testing different combos such as carbs and spacers
Thanks for all the replies. I spoke to BLP carbs and the venturi size is 1.375 but they can bore it to 1.450 and recalibrate the carb so I am going to send it out to try this, i should be close after this. The vacuum was measured off the engine builders dyno not on the vehicle itself.
raynman1969 wrote: ↑Tue Apr 03, 2018 8:17 am
Thanks for all the replies. I spoke to BLP carbs and the venturi size is 1.375 but they can bore it to 1.450 and recalibrate the carb so I am going to send it out to try this, i should be close after this. The vacuum was measured off the engine builders dyno not on the vehicle itself.
Good decision! I built same type carb using a 950 main body on my street 427 Windsor. Had the venture opened up to 1.475 with the 1.750 throttle plate. Made for an excellent running carb for the street and track!
Don't know your current dyno power but you could still make 600 HP with what you have.
If you will spend most of your time on the street you will probably never notice the extra top end but WILL like the crisp throttle response of the small carb!
Well there you go! If you have the extra coin to spend on the venturi job and you can't sleep without knowing what it could do with the modified 950....go for it. Otherwise I would leave it alone and enjoy!
What type car is it going in and what is drive train setup?
