[DeTomaso] [Fwd: Re: automotive related questions!]

[Rick Moseley]

720/4 = 180  (only 4 cyls per head/header)

But the reason for the crossing over was to improve/balance scavenging of
the adjacent cylinders in the firing order... not to be confused with the
physically adjacent cylinders.  Otherwise the firing order gives you a mix
of exhaust pulses of 90, 180 and 270.  By doing an over the top (or under
the motor as on the old  66-69 Fairlanes) crossing you could balance the
pulses in each header bank to every 180 degrees (theory). However, the
uneven tube lengths needed tends to slightly negate the desired effect
(practice). Ooooh, they sound good though!!!  Ford first used this at LeMans
on the 289s and later on the big block 427s.

But... equal length, stepped header tubes run into a TRUE "MERGE collector"
will get you as much scavenging as the 180's and are a dam-site easier to
live with and work on. 

Rick


-----Original Message-----
From: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com] On
Behalf Of Dave Londry
Sent: Wednesday, December 10, 2008 2:43 PM
To: DeTomaso Forum
Subject: [DeTomaso] [Fwd: Re: automotive related questions!]

720/8 = 180 ??

asajay at asajay.com wrote:
> It takes two revolutions to complete four strokes for all eight  
> cylinders, yes.  Each cylinder must make four strokes:  Intake (piston  
> goes down), compression (piston goes up), ignition (piston goes down),  
> exhaust (piston goes up).  So you see, exhaust only happens every  
> -other- time the piston comes up, so the crank has to make two  
> revolutions to complete one cycle.
>
> :)
>
> Asa Jay
>
> Quoting Dave Londry <davel at emspace.com>:
>
>   
>> 8 cyl every 2 revs or 720 degrees??
>> dave
>>
>> Paul - Home wrote:
>>     
>>> I have a few guesses and they are only guesses because the standard
>>> Chevy firing order also supports crossing the banks to get 180 degree
>>> headers.
>>>
>>> 1. It didn't fit well in the body work
>>> 2. They just didn't care to optimize that closely
>>> 3. They were running a flat crank which doesn't need to cross banks.
>>>
>>> For reference they are called 180 degree headers because each exhaust
>>> pipe will output once every 180 degrees of crank rotation.
>>>
>>> Paul
>>> #9270
>>>
>>> michael frazier wrote:
>>>
>>>       
>>>> Thanks for the info.  Any response on the 2nd question?
>>>>
>>>> Michael...it was in the 30s last night and the 50s today.  Looking  
>>>>  for a winter project since it's too cold to go outside.
>>>>
>>>> (2nd question: After looking at photos of GT-40s, Lolas, McLarens,  
>>>>  Chapparals, etc, I noticed the Ford poweredvehicles used 180s   
>>>> while the Chevy powered ones did not (generally). Any thoughts   
>>>> about that? Boat type headers?
>>>> I asked about building a set of Pantera headers like that awhile   
>>>> back. You could run longer tubes, a crossover pipe,
>>>> less connectors and simpler build while still getting the zoomy   
>>>> racy look for those who go just for that. Any thoughts on that one?)
>>>> _________________________________________________________________
>>>> Send e-mail anywhere. No map, no compass.


_______________________________________________

Detomaso Forum Managed by POCA

Archive Search Engine Now Available at http://www.realbig.com/detomaso/

DeTomaso mailing list
DeTomaso at list.realbig.com
http://list.realbig.com/mailman/listinfo/detomaso