Is it worth it?

[BLG355]

I am curious, at what point is it worth upgrading beyond the OEM TBI parts, for getting air in and out? Now, I know this can be a loaded question, so if anyone can answer it using my build, I'd appreciate it. Here is what I have going through my head. I originally build my truck to pass PA emissions, which for that year is a visual check, which it does, but I will now be under 5,000 miles per year and qualify for exemption, so I can modify.

Here the details:
1995 K1500 with 350, bored .030" over and now at 9.6:1 compression with 72cc dart s/s heads (165 intake). I used the Edelbrock 3704 intake because it retains the EGR Valve I needed. I have heard good and bad about this intake, but for me, at the time, it worked. Will I gain by going with a carb intake and an adapter plate? My cam is pretty much over at 5200 rpm. I also am running stock diameter throttle body have is shaved down. I thought about upgrading to a 454 TB or boring mine to 2" and making new throttle plates, but this would require something other than the 3704 intake. I just want to know if I am wasting time on this or if it would be worth it for up to 5200rpm. I am currently running stock manifolds, but they are going away for long tube ceramic headers this summer...so getting air back out is covered. I see so many different numbers about what the stock 5.7 TB flows, I don't want to be leaving untapped power on the curb. Any feedback is greatly appreciated. Thanks.

BLG

[steveo]

as far as throttle body size, for power bigger can be better, but throttle response can quickly become non-linear as you go 'too far', you end up a throttle that goes from closed plates to WOT at like 1/2 throttle, which is twitchy, and obviously any calculations that use tps will be out to lunch too

this is why guys that put bigass throttle bodies on electronic transmissions can have a hell of a time... and tv driven transmissions suffer an equally deadly fate.. since you're pulling WOT air but your tv cable is only partially cracked open... yipe

in my limited experience with tweaking big engines and too-small throttle bodies, without doing any math, monitoring vacuum under WOT with a fairly accurate meter can tell you if your TB is too restrictive

if there's restriction at the bores, you'll be pulling some amount of vacuum there when it should be damn near atmospheric (might want to do this test with the air filter off too... dirty air filter will give you lower than atmos. pressure at wot too..)

now im just learning about TBI, but from what i'm seeing... tbi looks pretty restrictive overall, i mean hell half of the bore is full of injector, so perhaps i'd go for broke...

[BLG355]

[QUOTE=steveo;40081]
in my limited experience with tweaking big engines and too-small throttle bodies, without doing any math, monitoring vacuum under WOT with a fairly accurate meter can tell you if your TB is too restrictive

if there's restriction at the bores, you'll be pulling some amount of vacuum there when it should be damn near atmospheric (might want to do this test with the air filter off too... dirty air filter will give you lower than atmos. pressure at wot too..)
QUOTE]

Awesome info right there. I looked at one of my data logs and I can see it in the log, KPA drops into high 80's at MAX RPM and WOT, so I do have room to grow.

Thanks,

BLG

[Roadknee]

The stock TB flows under 500 cfm at 1.5" Hg. On a 350 it's pretty well done by 4,500 rpm. A larger TB on the stock style 2 bbl intake will help some, but they are very limited by plenum volume. A good dual plane with an adapter would provide more plenum volume and better top end without much loss in low speed torque. I would even consider either an open spacer or milling the center divider out of the dual plane.

Years ago I saw a thread where fast355 had some experience running a VicJr 2bbl with a TB and claimed it ran very well. Folks with experience with than manifold claimed it would ice up when the ambient temp dropped below about 40F. I think this is because the VicJr has no heat crossover and the TB injectors don't do a good job of vaporizing fuel. This is probably why the stock intake routes hot water under and around the plenum. Point being if you go to an aftermarket intake, be sure to get one with exhaust crossover passages.

[steveo]

80kpa? damn, are you near sea level?

that's a pretty big restriction

[lionelhutz]

Where is your MAP plugged in and what are the specs on your cam?

When I was playing with TBI on a 350, I cut the ring around the injectors off the top of unit and smoothed the top of the TBI into the bores. I was running a Edebrock Performer intake with an adapter plate. The cam was a 220* duration, about 0.45" lift unit . It never logged anything on the MAP values that would suggest it was pulling a vacuum at higher rpm's.

[KidTurbo]

I thought about upgrading to a 454 TB or boring mine to 2" and making new throttle plates, but this would require something other than the 3704 intake. I just want to know if I am wasting time on this or if it would be worth it for up to 5200rpm.

I'd find a bigger throttle body for certain. Nothing cuts the power like limiting the air intake. NASCAR used the restrictor plate rule for two decades, because it works. No matter what you do to the rest of the engine, that stock TBI is gonna be your power limiter based on CFM's.

Not my specialty by any means, but what options are out there in small 4brl throttle bodies these days? My friend runs the largest FASS setup on a big CI Roush motor in his truck, but isn't there some more affordable options out there? I'd try to get in the 650-730 cfm range base on cubic inches alone. And as listed below, a good dual plane intake under it. Then those header will have something to flow..

[brian617]

Barry, what kind of air inlet/snorkle/air filter set up you running?

[Fast355]

The stock TB flows under 500 cfm at 1.5" Hg. On a 350 it's pretty well done by 4,500 rpm. A larger TB on the stock style 2 bbl intake will help some, but they are very limited by plenum volume. A good dual plane with an adapter would provide more plenum volume and better top end without much loss in low speed torque. I would even consider either an open spacer or milling the center divider out of the dual plane.

Years ago I saw a thread where fast355 had some experience running a VicJr 2bbl with a TB and claimed it ran very well. Folks with experience with than manifold claimed it would ice up when the ambient temp dropped below about 40F. I think this is because the VicJr has no heat crossover and the TB injectors don't do a good job of vaporizing fuel. This is probably why the stock intake routes hot water under and around the plenum. Point being if you go to an aftermarket intake, be sure to get one with exhaust crossover passages.

You are describing gasoline (and alcohols) latent heat of vaporization. If you took a pie pan of gasoline and set it in your driveway on a 100*F day, the pie pan would become very cool to the touch.

I never experienced icing, even in the middle of a snow/ice storm. But that being said, it was in an engine compartment that was very enclosed. I also had such an effective cooling system, that I had over 3/4 of the radiator blocked off by cardboard stuffed in between the radiator and condenser. The MAF picked up air right behind the radiator as well, not many choices for intake configuration on a fullsize G20 Van. I also played with running the system with the stock air cleaner housing and using the factory style hot air heat riser from the header tube. Really didn't make much difference either way in my application. It always took a 10+ minutes for the engine to warm up, idle down, and lean out anyway.

[BLG355]

80kpa? damn, are you near sea level?

that's a pretty big restriction

88kpa. less than 400ft elevation. at lower rpm's and WOT it's mid to high 90's, like 96 or so, and as RPM's increase to shift point at 5300 it's down to 88 or so.

[BLG355]

Barry, what kind of air inlet/snorkle/air filter set up you running?

It is all stock, except i have the Hypertech salad bowl into the air cleaner housing, which i am going to cut the housing back to match the bowl but haven't yet. I also removed the choke in the inlet of the housing, but i am running a stock air filter, no high flow or anything like that yet.

[BLG355]

Where is your MAP plugged in and what are the specs on your cam?

When I was playing with TBI on a 350, I cut the ring around the injectors off the top of unit and smoothed the top of the TBI into the bores. I was running a Edebrock Performer intake with an adapter plate. The cam was a 220* duration, about 0.45" lift unit . It never logged anything on the MAP values that would suggest it was pulling a vacuum at higher rpm's.

The MAP is plugged into the back of the throttle body. I have the top of the throttle body smoothed out pretty good. I am thinking if it isn't in the throttle body itself, it may be in the filter or stock filter housing setup. I'm not 100% sure the cam is actually done at my current shift points, even though its way in the upper end of what that cam can do, but the engine is definitely done, whether it's cam or air flow. I've used similar cams in the past and they pulled harder than this up to 5500, even 5800 rpm, so i think i have some kind of restriction somewhere. Here is cam specs, I have a .480" / .496" lift due to 1.6 roller rockers.



PART NUMBER:
211252/257
GRIND NUMBER:
RR-252/257


ENGINE INFO:
CHEVY SMALL BLOCK V8 305-350 CU.IN. 1988-UP
APPLICATION:



SPECIAL REMARKS:
HYDRAULIC ROLLER
PRODUCT USE:
STREET




http://iskycams.com/ART/dot_dkgray.gif


RPM RANGE: 1200-5000



Valve lift is calculated with zero lash and rocker ratio of 1.5


INTAKE TIMING

DURATION:

252
deg.


OPEN:
14
BEFORE TDC


CLOSE:
58
AFTER BDC


CAM LIFT:
.30"


VALVE LIFT:
.450"


VALVE LASH:
.
HOT





.
COLD



http://iskycams.com/ART/timingdiagram.gif
EXHAUST TIMING

DURATION:
257
deg.


OPEN:
60.5
BEFORE BDC


CLOSE:
16.5

AFTER TDC


CAM LIFT:
.310"


VALVE LIFT:
.465"


VALVE LASH:
.
HOT




.
COLD








LOBE CENTER:

112 deg.
OVERLAP:
30.5 deg.
CAM ADVANCE:
0 deg.




THE ABOVE TIMING IS CHECKED AT

.020

(OPEN) LIFTER RISE




.020
(CLOSE)





http://iskycams.com/ART/dot_dkgray.gif


The following timing is taken at .050" lifter rise and gives a more accurate determination of camshaft position.



INTAKE

DURATION:
204
deg.



OPEN:
-10
BEFORE TDC


CLOSE:
34
AFTER BDC



EXHAUST

DURATION:
209
deg.


OPEN:
36.5
BEFORE BDC


CLOSE:
-7.5
AFTER TDC

[lionelhutz]

That's a good low-mid range power cam and your throttle body should work fine with it. I'd try pulling the stock air intake off and then see what the MAP signal does.

[brian617]

It is all stock, except i have the Hypertech salad bowl into the air cleaner housing, which i am going to cut the housing back to match the bowl but haven't yet. I also removed the choke in the inlet of the housing, but i am running a stock air filter, no high flow or anything like that yet.

I'm also running the Hypertech bowl but my air cleaner bottom is cut open to match. I'm also running the factory snorkle with divorced heat riser and choke. One other trick I did to mine is use the early 90's flex tube and pull the hour glass center out of the fender mounted baffle. When looking around I noticed the 94-95 set ups are more restrictive. Easy trick to eliminate snorkle and baffle would be just to flip the air cleaner lid and record another WOT.

[jim_in_dorris]

Nice cam, I would have gone with the RR257/265 grind, but then I am a torque junky.

[BLG355]

Nice cam, I would have gone with the RR257/265 grind, but then I am a torque junky.

I wanted to go a little bigger, but at the time I was dealing with TBI Chips.com and I was told I can't go over 210@ .050, that it can't be tuned. I picked a smaller one that was within is tuning capabilities, which I later learned didn't exist. But overall I'm happy with it, good torque, good idle, pulls strong.

[Roadknee]

I wanted to go a little bigger, but at the time I was dealing with TBI Chips.com and I was told I can't go over 210@ .050, that it can't be tuned. I picked a smaller one that was within is tuning capabilities, which I later learned didn't exist. But overall I'm happy with it, good torque, good idle, pulls strong.

I think the cam you have is a very good choice in a 355 in a heavy truck. The larger one mentioned would pull stronger, although not by much, above 4,000 rpm at WOT. However, it would give up some low speed torque and part throttle response. If you increase the airflow into the engine as already discussed and install the headers your engine should pull strong through 5,200 rpm with proper tuning.

[jim_in_dorris]

sorry Roadknee, I have to disagree on the low speed torque and part throttle response. That slightly bigger cam actually has a lot more torque down low. I was not a big fan of Isky cams, ( I like lunati cam profiles) but the grind I mentioned actually has more area under the curve than the lunati cam I like. I model my builds in DD2003, and while I understand that actual numbers may not be exact, when you create a model and only change one part, it will give you a good indication of how that part affects the build. Of course, like always, I have been known to be wrong. I do however think that the cam he chose isn't a bad cam for his truck, just that I like gobs of torque.

[BLG355]

I think the cam you have is a very good choice in a 355 in a heavy truck. The larger one mentioned would pull stronger, although not by much, above 4,000 rpm at WOT. However, it would give up some low speed torque and part throttle response. If you increase the airflow into the engine as already discussed and install the headers your engine should pull strong through 5,200 rpm with proper tuning.

I was scared when I ditched the TBI heads that I would loose that idle-3000rpm grunt that it had, but I was very impressed with the ease this thing roasts the tires. It doesn't seem to have the throttle response I had from stock, but I am only running on a starter chip and will try to get some of that back. It's almost no fun to drive in the rain, a little burp on the throttle and the tires spin. I've been trying to get decent 1/8 and 0-60 times with the GTECH, but no luck, every time I get wheel spin, sometimes all the way through to second gear. I managed a 9.89 1/8 mile time one time, but I still left 25ft of black marks on the road...:confused: I'm not intending it to be build for speed, but it is always fun just to see what it can do. I'm excited to see what I can get out of it with some more upgrades this summer, it will be fun for sure.

[steveo]

I wanted to go a little bigger, but at the time I was dealing with TBI Chips.com and I was told I can't go over 210@ .050, that it can't be tuned.

"it cant be tuned.."

my junker is a 9x8 VE table.

i can imagine that would just SUCK if your cam didnt even operate in half of it, suddenly you'd have a 4x6 VE table, the rest would just be decel.

but it could be tuned, just not well, it'd probably be one of those 'as good as a highschool tuned carb' things.

ecm upgrade to something with higher resolution VE - problem solved?

[Fast355]

"it cant be tuned.."

my junker is a 9x8 VE table.

i can imagine that would just SUCK if your cam didnt even operate in half of it, suddenly you'd have a 4x6 VE table, the rest would just be decel.

but it could be tuned, just not well, it'd probably be one of those 'as good as a highschool tuned carb' things.

ecm upgrade to something with higher resolution VE - problem solved?

I have tuned a 230/230 @ .050 cam in a 305 with that same little VE table you are talking about. Works just fine!

[steveo]

no shit?

good to know!

[BLG355]

Well, I decided to bore the 3704 intake, even after reading about people having issues about going through to the water jacket. I figured f I go through I will just ditch it and get a decent dual plane anyways. I did the deep side tonight since it would take a lot longer. It is now 2.008". I am doing the short side tomorrow. And of course this post would be useless without pictures, so I attached some.


BLG

[Six_Shooter]

I have tuned a 230/230 @ .050 cam in a 305 with that same little VE table you are talking about. Works just fine!

IIRC my buddy's Olds BB, has something like 240* duration, and while it only uses the upper half of the VE table for idle (Idle KPA is around 55 KPA after a lot of playing and fudging to force it that low), it starts like a stock vehicle, and idles mean. During cruise MAP readings will actually go into the 40's.

It's not that it can't be tuned it's that it is more difficult to do.

[billygraves]

...........

[Fast355]

I gotta had it to you Mister!! YOU ARE RIGHT ON with the transmission pressures. At GM I learned why TBI used small throttle bodies and small runners. First was Emissions BUT with this is to keep the velocity in Motion inside the intake runners. If it slowed down, it would "Rain" and the fuel droplets would fall out of suspension, then run a liquid to the combustion chambers.
Second, the TBI engines usually run rich to keep the lean cylinders satisfied with fuel.
Port Fuel is the way to go if you select a intake that matches your requirements of your powertrain and the camshaft is selected.
Actually the TV trans should have parts to increase it's pressure overall. If it's a L60/65/70-E I still would add pressures. For the most part the L80 has enough pressure cushion to be pretty safe. (Unless it's a very hi torque engine or S/C or turbo)

Or a Duramax! I had to put extra pressure in that tune by eliminating what the tune was pulling during shifts.