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-   -   Some interesting infromation for building a Street / race BBC (http://www.hotrodders.com/forum/some-interesting-infromation-building-street-race-bbc-104087.html)

Bad Rat 12-08-2006 06:29 PM

Some interesting infromation for building a Street / race BBC
 
Here is a interesting link for a flow comparison of rectangular port and oval port BBC heads,, also a good build comparison for a 468 BBC to a 432, nitrous motor,, http://www.maliburacing.com/ovalvsrect.htm for you guys thinking about building a good street and 10 sec, race motor,, :thumbup: Bill

Bumpstick 12-08-2006 06:57 PM

An interesting article for sure... Might also be the reason I have 5 sets of large ovals (781`s & 049`s and some real cool semi-closed large ovals)

But just something to point out... The standard installed height of the valves in an oval port head is 1.880 which limits the spring you can use and the the lift considering coil bind, also the guides have to be machined to use anything over a .550 lift cam... Will cost more to modify for the .100 lift but still darn good heads for street/strip apps...

Rectangle port heads... Well that 026 casting I`m not to sure about...? Never even seen one, but the 188 & 990 castings have proved themselves just a time or two... Also installed heights of 1.950 or higher are a snap and no rotator eliminator is needed on the exhaust as with ovals... A solid roller with big lift is no biggie with the 188 or 990 and without a doubt on a big inch motor and RPM`s over 6500 the rectangle ports shine...


The app and your budget tell the tale... :thumbup:

Bad Rat 12-08-2006 07:07 PM

[QUOTE=Bumpstick]An interesting article for sure... Might also be the reason I have 5 sets of large ovals (781`s & 049`s and some real cool semi-closed large ovals)

But just something to point out... The standard installed height of the valves in an oval port head is 1.880 which limits the spring you can use and the the lift considering coil bind, also the guides have to be machined to use anything over a .550 lift cam... Will cost more to modify for the .100 lift but still darn good heads for street/strip apps...

Good point,, The cam I ordered is the Comp,414 nitrus/ blower with 566 in. and 575 Ex.. hyd roller,, we were concerned about piston / valve clearance,,
the 411 comp cam [ nitrous/ blower is 537 and 541,, would this be a better choice,,?? Bill

Bumpstick 12-08-2006 07:17 PM

If using aftermarket pistons there should be no problem but of course this needs to be checked... The factory LS7 cam was .600 lift but of course this was with the 188/990 heads so the ovals may be somewhat different in valve clearance...?

The lower lift cam would work no problem for sure and no need to machine the guides too... With the larger lift cam the guides will need work (.125 off should be fine) But also depending on the pistons valve clearance needs to be checked on anything over .550 lift... The 781`s that I`m running were fine even with .604 lift on the intake side but was using 1.8 ratio rockers and have aftermarket pistons... I swapped back to 1.7`s and saw less valve train noise and for sure less abuse...

Bad Rat 12-08-2006 07:23 PM

we are using after market pistons,, flat top,, the machinest was a little concerned about valve clearance,, I already ordered the bigger cam,, from summit,, but it hasn't arrived yet,, If need be I could probably trade for the smaller one to avoid the added expense,, just for a small differance in lift,, Thanks Bumpstick,, Bill


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