quote:

Originally posted by RacerVX54:
SO a good friend of mine just installed a 192 blower shop blower on his 421 SBC this motor made around 650 before. Dynoed yesterday was 1031 hp not sure what the tor number where.

So my buddy made it to the track yesterday. Car ran 5.80's-90's before. His first pass pulling 10 degree at the hit for .5 secs. 5.30 @130 with a 1.20 60 then went a 5.288 and a 5.286. This thing isn't even turned up. I am impressed to say the least.

I'm thinking about putting one of these on a back half car over the winter to get some more top end pull. I would assume my 950 cfm 4150 isn't going to be enough air with a blower. I have an 1150 dominator on the shelf.

Question is does the normal CFM requirement calculation work if you include the added cubic inches of the blower. So if I put a 250 blower on it would the effective calculation be

(((468 (True CI) + 250 (blower CI)) * 7000 (rpm) / 3456 = 1454 (req cfm @ 7000 RPM)???

Seems like a lot but then again forced induction and I've never had anything like that before so I'm a newb.

That’s definitely not right.

The airflow is not additive and 250 refers to cu.
in. Per revolution of the blower.

So if you’re spinning the blower 1:1 with the engine it should act like a 500”
Na engine (only 4cylinders fire per rev).

Most guys are spinning these upwards of 1.5:1 or higher I think.

It’s not really going to act like a 750” engine though because the blower efficiency falls off.

I would look at it more like this:

At a certain ratio the blower is going to make 1200 hp at a bsfc of about 1.3:1. So that’s 1560 lb/h of fuel. At an afr of 4.8:1 you need 7488 lb/h of stp air. That works out to 1600 cfm. Do you really need 1600 cfm worth of carb? Absolutely not, that’s just how big the carb would have to be for the pressure drop (restriction) to be negligible.

I would be more concerned with fuel flow capability.

quote:

Originally posted by BJs Wild Ride:
That’s definitely not right.

The airflow is not additive and 250 refers to cu.
in. Per revolution of the blower.

So if you’re spinning the blower 1:1 with the engine it should act like a 500”
Na engine (only 4cylinders fire per rev).

Most guys are spinning these upwards of 1.5:1 or higher I think.

It’s not really going to act like a 750” engine though because the blower efficiency falls off.

I would look at it more like this:

At a certain ratio the blower is going to make 1200 hp at a bsfc of about 1.3:1. So that’s 1560 lb/h of fuel. At an afr of 4.8:1 you need 7488 lb/h of stp air. That works out to 1600 cfm. Do you really need 1600 cfm worth of carb? Absolutely not, that’s just how big the carb would have to be for the pressure drop (restriction) to be negligible.

I would be more concerned with fuel flow capability.

Great answer thanks!

Someone had mentioned adding a second keyway. This may be a quick, low cost simple solution for you.

https://www.alkydigger.net/pro...hp?prod=AD-BBCpinkit

Crank does not have to come out of motor and be sent out. Solid and secure and reasonable priced.

If I was building a blower motor from scratch I would have the keyway on the crank machined but if I was just going to put a baby Blower on top of existing motor this would do same thing and give you security it is not going to move.

A second crank key not needed for these little blowers.Not that its bad idea to have if you are building motor or having built,even if you do not use it right away. Most blower motors did not have dbl keys till they got to where they where making bunch of boost,spinning them 50% od and it is taking 300 plus hp to spin the big blowers,well the roots blowers.

I have a 8-71 high helix on my sbc and my dad has a 250 on his 598. I bought my 8-71 a little before the 250’s became popular and can say knowing what I know now, the 250 would have saved me almost half the money and been plenty for my goals. My dads car was on average a 5.20’s@133 NA. It gained roughly 80-100 pounds (don’t have the pre blower weight in front of me) and weighs 2740 lbs now and has been 4.84@144 with 5.5-6 psi. Only thing we did was put a thicker head gasket on, double keyed the crank, and used the hemi style balancer. He is running the same converter and carbs as he was NA. He has some beadlocks on the way and we are still fine tuning the chassis and tire choice, but I believe come this fall we will see a high 70 out of it.

Whats the normal compression for one of these builds?

I don’t know what normal is but dads is 13.7 because we know the 250 won’t make more than about 8ish psi at his cubes. My sbc is at 11 just to keep a bigger tuning window as I go up on boost.

There's nothing like bringing your own atmosphere to the starting line with you.

quote:

Originally posted by 70 Mach 1:
I have a 8-71 high helix on my sbc and my dad has a 250 on his 598. I bought my 8-71 a little before the 250’s became popular and can say knowing what I know now, the 250 would have saved me almost half the money and been plenty for my goals. My dads car was on average a 5.20’s@133 NA. It gained roughly 80-100 pounds (don’t have the pre blower weight in front of me) and weighs 2740 lbs now and has been 4.84@144 with 5.5-6 psi. Only thing we did was put a thicker head gasket on, double keyed the crank, and used the hemi style balancer. He is running the same converter and carbs as he was NA. He has some beadlocks on the way and we are still fine tuning the chassis and tire choice, but I believe come this fall we will see a high 70 out of it.

Do you happen to know the overall cost for the 250 blower kit? Bower, intake, balancer, pulleys, etc.... (Basically looking for the overall cost to add it to my setup)

From what i have seen its about $3400 for a BBC kit with a 250 blower shop blower. https://www.alkydigger.net/products.php?cat=218

Not sure what "normal" is when you talk about a 250 blower combination, but my 598 is right at 13.5:1, didnt' change a thing, added the 250 and went racing. I have the 67 bottom 33 top, i've seen 9 psi when the weather was good 1000' and less, pulling 13 degrees at the hit putting it back in at 0.6 went 1.02 to the 60, 4.45 at 155 on its fastest pass. The gage is the simple check valve system and small fuel pressure gage so i'm not sure how accurate the numbers are. Car weighed 2000 lbs before the blower, shipping weight was 125 lbs on the kit, i'm guessing its 2125 to 2150 once everything associated with the blower conversion was bolted on.

When i take it out to freshen it i'm going to double key it, swap to the hemi pattern balancer, and see if i can figure out a set back plate for the front to eliminate the need for the 2V adapter pulley deal that's bolted to the harmonic balancer, i don't like them, it pushes the load on the crank that much ****her out. They only make 2 snout lengths a long one and a short one, long one uses 3 V adapter short one uses 2 V adapter. The V means v grooves in the pulley adapter that bolts to the front of the harmonic balancer and the blower pulley bolts to that which has the hemi bolt pattern in it on one side and chevy pattern up against the balancer.

As long as you run a good valve spring, use a 3 step if your injected, and maintain your stuff like normal they seems to be easy on parts.

My 598 with 250 blower has been a best of 4.35 in the 1/8 and I've made 1- 1/4 mile pass 6.84 @196
My car weighs 2170 with me in it.. compression is 14:1. My normal timin retard is 5 degrees out from the hit and all back in @4 sec. I bracket race it usually in the 4.45-4.50 area.. Goes 1.05 60...

Looks like the kit dad has is $3600 for a tall deck bbc with the 8mm pulley set up (we did not care for the serpentine belt). That comes with everything to install the blower and get it running. He also purchased the belt drive billet crankshaft mandrel to run his vacuum pump for $129. Extra blower pulleys are $111 each. We had to get some new longer bolts when we added the mandrel, but picked them up from the local hardware store. I don’t remember the exact price of the harmonic balancer, but $400-450ish. Not really sure that the double key way is necessary for the 250, but we did it since we pulled the motor for freshening. We also had to add the RBZ water fill neck since his radiator does not have a radiator cap since it is lower than the motor for $185.

Rick 4310,

That's rolling. Nice combo.

Who's converter? Flash RPM? Finish line RPM?
Rear Gear?
Carb or Inj?

With all of the extra air being pulled into the engine, I'd assume even my little 468 would need a dominator more than likely?

I saw a dyno sheet between one carb and two with a 250 blower and it picked up 100hp. That was the only change. I think these things want as much air as they can get.

quote:

Originally posted by Bob Payton:
I saw a dyno sheet between one carb and two with a 250 blower and it picked up 100hp. That was the only change. I think these things want as much air as they can get.

only a 100 pick up is way down from what i have seen around here.

quote:

Originally posted by Rick4310:
My 598 with 250 blower has been a best of 4.35 in the 1/8 and I've made 1- 1/4 mile pass 6.84 @196
My car weighs 2170 with me in it.. compression is 14:1. My normal timin retard is 5 degrees out from the hit and all back in @4 sec. I bracket race it usually in the 4.45-4.50 area.. Goes 1.05 60...

What a great, fast bracket combo. I'm assuming that timing is back in at .4 seconds? You may have said, but how much boost is that?