Intake Selection

[Vetteboy]

Hey,

I am looking to put fuel injection back into my C4 (1986) as it was removed by the previous owner for an LPG conversion. I run a mild 400 driven daily. Does anyone know the suitability of the standard TPI setup of a corvette for a 400? Do I need something with more capacity?

Thanks in advance...

[77CVT]

I would imagine it would be restrictive up top as the TPI is more for low down torque.  I think you'd have to have pretty big runners?

Anyone care to chime in?

[Ausrs]

there are people running 383 with tpi BUT with mods like large tube runners etc .......if you wanted to go the efi route i would suggest something like a superam
cost in aus is going to be mega $ though :(
http://www.gmhightechperformance.com/tech/0307htp_holleystealth/
some info from thirdgen.org
the HOLLEY STEALTH RAM FLOWS at 275cfm out of the box, can easily reach 300cfm with minor port work the stock TPI has a hard time flowing 230cfm even with minor port work, look here
most of this info is right off the accel,holley,edelbrock, and TPIS sites, add a little math and the results become much clearer!!!
GETTING YOUR Intake....... length ....... port in -- out
Stock GM Base--- 6.375"------ 1.47"- 1.96x1.2
TPiS base------ -6.125"------ 1.75"- 2.09x1.28
Accel base----- -6.125"------ 1.75"- 2.09x1.28
Holley base------- 6” runner 2.3”- 1.9”x 1.23 (2.337 sq inches)
Runners
Stock TPI----- -- 7.250"------1.470" round(1.70 sq inchs)
SLP ----------- - 6.625"------1.600" round (2.01 sq inchs)
Accel LTR------- 6.625"------1.615" round (2.05 sq inchs)
TPiS----------- 7.625"------1.660" round (2.168 sq inchs)
Mini ram -----3.5”
LT1 ----------3”
Runners (measured individually)
Stock....................203.17 cfm
ACCEL................242.02 cfm
Extrude/ACCEL...275.83 cfm
Super Ram............289.18 cfm
Intake manifold with 3/8 inch radiused intlet
.............................222.45 cfm
Holley stealth ram ………..275cfm
Stock intake manifold with runner
Stock....................198.72 cfm
ACCEL................213.52 cfm
Extrude/ACCEL....217.11 cfm
Super Ram............220.67 cfm
Holley stealth ram …..275cfm

ACCEL Hi-Flow intake manifold with 3/8 inch
radiused inlet.........251.51 cfm
ACCEL Hi-Flow intake manifold with runner
Stock....................215.83 cfm
ACCEL................232.53 cfm
Extrude/ACCEL....243.21 cfm
Super Ram............240.24 cfm
Extrude-Honed ACCEL Hi-Flow intake
manifold with 3/8 inch radiused inlet
............................275.83 cfm
Extrude-Honed ACCEL Hi-Flow intake
manifold with ACCEL runner
............................266.94 cfm
Edelbrock Performer RPM manifold
(Stock)..................286.51 cfm
Edelbrock Victor Jr.
.............................275.24 cfm

HOLLEY STEALTH RAM
Stock…………………………… 275cfm
Ported…………………………..300cfm
Runner lengths
Stock tpi manifold 8” runners 11.25”, cylinder head 6” total 25.25”
Accel super ram manifold 8” runners 7” cylinder head 6” total 21”
Holley stealth ram manifold 6.26” ” cylinder head 6” total 12.26”
Edelbrock performer RPM runners 6” ” cylinder head 6” total 12”
Edelbrock vic jr , runner length 5.5” ” ” cylinder head 6” total 11.5”


Now play with the figures in the calculators below, what youll find is that the if your using a 350 size engine as a guide BTW THE INDICATED Torque PEAK IS WHERE THE CYLINDER FILLING EFFICIENCY TENDs TO PEAK due to RUNNER CROSS SECTIONAL AREA,AND THE HP PEAK RANGE IS WHERE THE RUNNERS TEND TO BE MOST EFFECTIVE, DUE TO HARMONICS/INERTIA in THE AIR FLOWING THRU THEM THATS WHY THEY ARE SOMETIMES A FAIRLY WIDE RPM RANGE SPREAD. you can of course raise the tq peak with cam timing and porting and differant header designs but the harmonic range will tend to stay fairly steady in the intake ports, and yes increasing the displacement tends to lower the rpm ranges

the tpi runner length is ideal for peak tq 3427rpm and 2700-4000rpm for peak hp

the super ram is ideal for peak tq at 4032rpm and 3300rpm-4800rpm for peak hp

holleys stealth ram runner length is ideal at 4700 for peak tq and 5618rpm to 6282rpm for peak hp

the mini ram and lt1 intakes are ideal for peak tq at about 5200rpm and 7244rpm to 8101rpm for peak hp

now KEEP FIRMLY IN MIND the engines tend to enter valve float and get close to engine red line by 6300-6700rpm depending on your combo' after running all the available combos, Ive found a HOLLEY STEALTH RAM is CURRENTLY THE BEST CHOICE,ESPECIALLY IF MATCHED TO GOOD CYLINDERHEADS AND THE CORRECT CAM
all Im trying to show here is that it makes no sence at all to try and feed cylinder heads,cams,ETC. with an intake that flows LESS air than THEY do, THE CYLINDER HEADS SHOULD ALWAYS BE ABLE to OBTAIN AT LEAST 100%- 110% of thier POTENTIAL MAX air flow or your RESTRICTING the ENGINES HP





http://www.rbracing-rsr.com/runnertorquecalc.html


http://www.bgsoflex.com/intakeln.html

[Vette Obsessed]

The short answer to your question in my opinion is yes.

The Stealth Ram is a very interesting intake alternative but there is one problem when using it on a C4 application:  It won't fit under a stock height C4 bonnet. :20

I got my SuperRam at a very good price but the whole setup was still far from cheap.

The stock TPI setup is designed for a 305 motor - the setup is the same whether installed on a 305 or 350 - it just happens to choke the 350.  If you are running a 400 I wouldn't waste my time or money with a stock TPI setup.  It will work but I think it will be a major restriction.

You can always go with a Miniram as well but again that isn't exactly cheap either.

Like AusRs says, each of the above intakes has different flow rates and might be better suited to a particular powerband than another intake.  In general, on a stock 350 a stock TPI will literally run out of puff around 4500rpm.  Using bigger runners and a bigger base will lift that to around 5200rpm.  A SuperRam, when matched with the right cam runs out of puff around 5800-6200rpm.  A Miniram is good for 7000+rpm but with a tradeoff in torque down low.  The Stealthram falls somewhere between the SuperRam and Miniram and is probably the best priced but there is that small problem of not fitting under the hood...

I guess which setup suits your car best depends on the cam in it and your budget.  Hope this helps.

[87Z51]

Lt1 manifold can be adapted to fit earlier (L98 ) blocks.Needs hole machined for dizzy and water outlets in front of manifold.Will allow a big cube motor to breathe without too much loss of bottom end torque.
Can obtain complete in Aust for less than A$700.
Know anyone with a drill.

[Ausrs]

lt1 intake on an sbc at best is an abortion with remote t/stat housing and mods to be made on many things including the seroentine belt setup
stick with a stealthram or ltrunners and ported/siamesed tpi base
have a look at http://lt1intake.com/  for what needs to be modded for lt1 manifold to suit

[Vette Obsessed]

When I first heard about the LT1 intake conversion it sounded like a great proposition.

However, the feedback I have seen from people who have tried it in the States has been far from good.  One report I saw stated that the person who bought the "converted" intake had to do a large amount of finishing just to get the thing to fit onto the motor.

I agree with AusRs that large tubes or a stealth ram would be the most economical way to go if you have a mild setup.  The superram has the potential to be a good setup but it is far more expensive than large tube runners and a ported base or a stealthram.

I think there may even be a Vette conversion for the Stealth ram plenum to allow it to fit under an unmodified hood.

[Vette Obsessed]

http://fasterdeals.com/vette/index.html