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-   -   BBC Blower and characterisic idle surge (http://www.hotrodders.com/forum/bbc-blower-characterisic-idle-surge-67213.html)

66GMC 08-01-2005 03:33 PM

BBC Blower and characterisic idle surge
 
Hi Folks,

I'm just dreaming at this point... :mwink:

I recall an announcer at the drag strip talking about the idle surge that (according to him) is "common to every Blown Big Block Chevy".

Is this true? Of EVERY blower?

There is a B&M blower complete w/ carb and bird-catcher on racingjunk.com that the seller is asking $1800.00 for. Seeing as how I am already shopping for an intake and carb (my 454 was on propane) I may even be able to convince myself that the additional cost could be "justified" :P ... it would just take a little longer to save for. :mwink:

I guess the thing that I'd like to know is: Is a blown 454 /TH400 automagic combination "streetable"?
Would it "behave" at idle, or would it be a strain on one's nerves (and brakes) sitting at a stoplight? What kind of stall speed would a guy need?

I understand that lower CR is better ... what 8.5 max?
I have recently agreed to purchase some 98.5cc heads, but the same guy has some 049/781 (113.0cc) heads as well. Would they be a better choice?
Forged pistons would be a "for sure" requirement?
OK on a 2-bolt main?
What kind of camshaft would you use with a blower?

Don

NXS 08-01-2005 04:51 PM

Quote:

Is this true? Of EVERY blower?
No, it comes from high boost levels or a narrow LSA cam
Quote:

Is a blown 454 /TH400 automagic combination "streetable"? Would it "behave" at idle, or would it be a strain on one's nerves (and brakes) sitting at a stoplight?
It depends on your cam/compression combo
Quote:

What kind of stall speed would a guy need?
One that matches your cam
Quote:

I understand that lower CR is better ... what 8.5 max?
Depending on boost levels. I've heard propane can handle more compression but I've never ran propane.
Quote:

049/781 (113.0cc) heads as well. Would they be a better choice?
It depends what you want to do.
Quote:

Forged pistons would be a "for sure" requirement?
What is the intended use and boost level you're shooting for?
Quote:

What kind of camshaft would you use with a blower?
On the street a nitrous/blower profile with a wide LSA {112-114*}. :)

topfuel 08-01-2005 08:51 PM

The idle surge or roll that you refer to is mainly caused by the idle mixture or by using carbs that aren't boost referenced. The power valve is opening and closing due to the varying vacuum signal the carbs see on top of the blower making the mixture rich then lean. I can make the idle of the blown big block in my boat roll or be smooth by adjusting the idle mixture screws. It seems that alot of people like the "detroit roll" sound. I don't personally, but to each his own. The cam I am running in my boat would be a good street cam also. It has 224 deg. of int. duration and 234 deg of exhaust dur. with 114 deg. of lobe sep. The lift is .545 int. and .560 ex.

By the way, I am running a B&M 420 series blower.

I hope this helps. :thumbup:

Tech @ BG 08-02-2005 07:09 AM

Idle Surge.
 
Idle surge is caused by the engine not being tuned properly, or the improper parts being used. I've got multiple Blower Engines, and the little motor 468" runs 9.2:1 compression, and 7.4 lbs of boost. It idles at 880 RPM and has absolutely no surge what so ever. You have to first pick the proper parts, and then tune them properly.

jameskirk1 08-02-2005 04:23 PM

Forged pistons are more resistant to detonation than either cast or hyper, but if your engine is tuned right, you won't encounter detonation...I run hyper pistons in my 144 blown 355...

Two bolt mains are fine as long as you keep the RPM's reasonable...You will have so much freaking torque you won't need to wind it anyway...My engine is limited to 6000rpm max...

Look for a cam with wider lobe seperation, and more lift and duration on the exhaust side. I used a Comp Nitrous HP grind in my engine and it performs great. Smooth idle and pulls like a raped ape to redline...

I would also like to add that modifying an existing carburetor for a blower motor can be a real headache unless you are a carb guru...I went with a 750 Mighty Demon and haven't looked back since...:D

I would also add that you really need to watch your fuel system and make sure it is up to the task of fueling the beast...Just personal experience...BEST OF LUCK!

66GMC 08-02-2005 08:18 PM

Is your blower similar to this?
 
Quote:

Originally Posted by topfuel
By the way, I am running a B&M 420 series blower.

I hope this helps. :thumbup:

Yup these replies are just exactly what I wanted to hear! Thanks to you all!

TopFuel:
Is this similar to yours?
http://www.racingjunk.com/exec/ca/vi...OWER-CARB.html

Here's a quote from a previous post that got me started on this.. 450HP/600TQ sounds like a whole lotta fun :thumbup:

Quote:

Originally Posted by 454C10
Or slap a small blower and a "blower cam" on the stock engine and make some decent hp and some major torque. 7 psi on a smogger 454 would get you about 450 hp and 600 ft lb of torque.



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