I'm about to get started with my stage 2 mods ( porting heads, LPE 219 cam,
Hooker SuperComp headers, AFPR ).
Should I also siamese intake base while engine is apart?

What could I gain and what could I loose?
What do you think?

 

TTT :lurk:

 

Ive been moding and porting and trying differant combos of runners,bases ,cylinderheads and cams for about 12 years now on TPI corvettes, I own 3 c-4 corvettes
IVE BUILT and TESTED SEVERAL DOZENs TPI ENGINES,PORTED DOZENS OF INTAKES, helped tune and MILDLY MODIFY DOZENS OF ENGINES, DONE MORE CAM SWAPS THAN I CAN REMEMBER
PORT THE PLENUM...............YES
PORT THE RUNNERS ............YES
PORT THE CHEVY BASE,..........YES
SWAP TO SLP RUNNERS ..........YES
SWAP TO ASM RUNNERS .........YES
SWAP TO BIG MOTH BASE........YES
SWAP TO EDELBROCK BASE.....YES
ACCEL BASE............................YES
siamese the runners in the base,NO!, it allows the engine to rev easier but you loose most of the ram tuneing effect

if your engines still highly restricted after porting the TPI intake
you need to swap to one of the better flowing aftermarket intake systems
http://www.thirdgen.org/newdesign/te...meseport.shtml
http://www.gtiworld.fsnet.co.uk/porting.htm
http://www.ws6transam.org/ported.html
http://www.sa-motorsports.com/diyport.htm
http://www.babcox.com/editorial/ar/eb120121.htm

http://www.eecis.udel.edu/~davis/z28...16siamesebase/
PORTING THE PLENUM DOES HELP


porting the runners helps

http://www.thirdgen.org/newdesign/te...meseport.shtml

this does NOT HELP in any car Ive worked on, YES it increases the rpm range BUT you loose MOST of the ram tune effect ,read this
http://www.eecis.udel.edu/~davis/z28...age021105.html

the big strong point the TPI intake injoys is a VERY STONG RAM TUNE EFFECT due to its long collum of air haveing built up inertia in the intake runners, cutting some length like the super ram does raise the rpm levels slightly (A GOOD THING)
siameseing the base raises the ram tuneing rpm to about 15000rpm (well above what you can reach

Computation Results:
Input length is 5 inches (2" runners+cylinder head port length)
For 2nd harmonic, RPM range is from 23496 to 28512 with a pulse strength of 10 percent
For 3rd harmonic, RPM range is from 17654 to 20176 with a pulse strength of 7 percent
For 4th harmonic, RPM range is from 13764 to 15392 with a pulse strength of 4 percent


[Modified by grumpyvette, 10:01 PM 6/18/2003]

 

Grumpy...to all of the stock TPI's that loose traction from the start...then runs out of steam right after it hooks up, it helps a lot. Especially for a free mod. ( And when your married and saving to buy a house...free counts!)


And..as for your math...higer harmonics always occur at a higher frequency...meaning higher RPM's, you have them listed as lower rpm's for higher harmonics.

As for runner length, the basic 4 barrel single plenum intake has a total runner length of about 5 inches total in the center cylinder runners/ports...yet they are tuned perfectly for mid rpm power (and make just as much power at low rpm's as a tpi does.)

I can agree that eht pictures above show a little too much siameesing...should stop at about 2" into the base with no knifeblading of the edges ( knifeblading reduces scavenging and total velocity)

Basically...what I am saying is everyone who has done it liked it, and dyno charts all show improved max torque over stock tpi's and a higher rpm powerband which makes it hard for me to believe you would recommend against it.




[Modified by BBA, 12:39 AM 6/19/2003]

 

either way it sounds like a winner when you have forced induction....

 

All I can tell you is the results found on over a dozen trys at this, anything that opens up the ports and smooths flow seems to help, shortening the runner lengths up to a point helps raise the engines rpm levels, but the best compromise I found way with a fully ported base and plenum and fully ported SLP siamesed runners with the divider removed for the upper 3", what you basically have is the same port size and runner lenght as a ported super ram in that runner size and lenght, but a slightly smaller plenum volume. when we siamesed the base runners the engine did rev easier but lost mid and low rpm tq, enough that the track times did not improve yet we lost a small amount of drivablity, we swapped back to the un siamesed fully ported base and everything again was great, Im not saying siameseing the base won,t increase air into the cylinders, slightly IT WILL, BUT IT WILL ALSO CAUSE THE LOSS OF ALMOST ALL OF THE RAM TUNING the runners provide!
your better off with large ported runners in the base that extend at least part way up the runners from a well ported base towards the plenum, port the max out of the plenum and siamese the upper 1/2 of the runners, thats where you gain the most for your efforts.
siameseing the base only allows a increase in air flow, with no ram effect,you get some but not all the potential improvement you could have by doing it correctly

btw a 5" 4 barrel intake runner is acctually about 8" long, your forgetting the 3" of intake port length in the cylinder heads

a TPI is working with close to 20" of runner length measured from back of the intake valve to the plenum
a super ram drops that to about 16"
a stealth ram significantly opens the port size and drops the length to abou 9"
siamesing the TPI bas drops it to abou 5" but the ports remain (EVEN PORTED ) smaller and less able to feed air into the cylinder heads


[Modified by grumpyvette, 4:47 PM 6/19/2003]