GREGGPENN

After looking thru various websites, I found the following stats:

Early C4 cam lift is .415" (1989 cam)
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Here are some intake flow numbers for #113 heads from TPIS "Insider Hints":
Lift......Stock......Ported
.100"......62...........68
.200".....116.........149
.300".....161.........193
.400".....185.........211
.500".....195.........211
.600".....198.........211
Note that the "Ported" numbers were with 1.940" intake valves.

My observation: with a cam lift of .415, max head flow (during max valve opening) couldn't exceed much more than 185cfm.......
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Stock TPI base flows about 200cfm
Runners flow about the same.
Together they may drop to 181 but it might be a little more.... (websites weren't clear on this).
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TB flows enough to feed a 350 @ 6000rpm+ (650cfm I think)
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Motor sucks air in pulses but those pulses include the whole stream from head to base to runners to plenum. Not sure if higher flow is necessary in any part of the stream to compensate for intermittent pulse (flow).
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Plenum has 90-degree turns into runners, humps between runners, and humps behind butterfly valve. All of these can obstruct smooth flow
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Questions/Conclusion:
I understand there is more to it than static flow (like volumetric efficiency, exhaust scavenging, etc...) but I'd think flow is flow. By definition flow is restricted to the lowest flowing part of a stream. If the heads flowed less, the intake couldn't help and visa versa, right?

Is this the main reason people notice little-to-no difference when converting to a big mouth base/lt runner setup? And, w/o any flow data on the plenum, is this really the piece where the most difference can be made by porting?

The SR setup has a much bigger plenum which seems more able to feed the runners. They lack the "humps" that block immediate entry behind the butterfly and they don't block flow into the runners. From my perspective, porting the plenum is the only place that the stock INTAKE setup might be improved for a stock motor. (I understand this changes with head/cam, but that's not the issue). Am I right/wrong?

Gregg

Note: 84-88 heads and cam flow similar to the 1989. I understand iron heads were a larger cc but the general flow seems about the same for all TPI years.

cv67

I dont think pleunm size has much to do with it,look at a carbed intake, they are small and do just fine. IMO overall runner length may determine how much air overall will flow through there. Im not down with the whole science of it but makes sense in real life. Removing obstructions will always help but may be more noticeable on a short runner manifold

KeyWestJack

65Z01

The stock base & runners will flow 198cfm which is enough for the stock heads & cam.

Stock runners alone will only flow to 203cfm so adding an Accel base only will not flow enough for ported #113 heads.

However, the combo of Accel heads w/ AS&M runners will flow 233cfm, enough for even more agressive porting.

Note that the stock base w/ AS&M runners will flow214cfm, enough for a mild port job.

The stock L98 intake has enough flow for the stock cam & heads through the stock RPM range.

However, take a look at the before & after dyno data on the siamese intake base. Though peak power didn't increase the rpm range was much increased, i.e. notice how much flatter is the hp curve above 5k RPM.
The reason for this change is not increase in static intake flow, rather in the dynamics of flow at high rpm.

Matt Cramer

Flow numbers are measured at a given pressure drop. If the heads, base, and runners all flowed 200 cfm at 28" of water, for example, if you were running the engine fast enough that you had 200 cfm of air flowing through it, the total pressure drop would be 84" of water, or around a 3 psi pressure drop. The numbers aren't supposed to be matched to each other.

Firevette

Take it for what its worth, but I consistiantly run .15 to .2 faster in the 1/8th after my big mouth, SLP runners, Home ported plenum, and 52mm Tb. I know its not a huge difference, but it seems there was some room for improvement.

65Z01

I believe Vic'89 saw similar gains from the Accel base w/ AS&M runners.

That gain is due to improved breathing at the top end not, I believe, to any increase in peak HP.
Do you see an increase in trap speed or only in ET??

Remember that the TPI runners limit breathing at high RPM not due to static flow restriction but due to the dynamics of cylinder filling due to the long tube runners. So increasing runner diameter, shortening the runner length or siamesing the base all aid high RPM breathing.

hexane

I have experimented with even a ported TPI intake and really it still had very little left past 5000 rpms. Its just better to upgrade to something better.

I know the stock 113 heads as cast on the intake flow 190ish @ .500 stock. That is super crappy for a supposed "performance aluminum head." So it is really much more worth it to buy performance heads vs. porting them.

I feel like I wasted my time porting my 113s to give them a second chance. I did notice a slight improvement up past 4000 rpms, but still that is not enough. Maybe the 1.94/1.50 valves are to blame. The performance still felt less than the Dart irons I was experimenting with for awhile. The Dart irons as cast with 2.02/1.60 valves still felt a lot stronger up there and seemed to pull much better at all the rpm ranges. That is just an experience that I'd like to let people know that the stock heads aren't really worth investing time on, unless you have nothing else to do.

GREGGPENN

You are returning the numbers I was seeing... However, if the stock base alone flows at 200cfm, I don't see how ASM runners could increase the flow to 214. (I noted 200cfm at 3rdgen, Vader, and StealthRam's website which all show the same #s).

Posts so far seem to confirm that altering the base & runners really won't do much.

I particularly appreciate observation on head porting. 113 head porting is advertised to gain about 30hp. base and runners 20hp. This would imply 50hp by doing both. Probably ain't gonna happen, right?

gp

GREGGPENN

Don't suppose you could translate....

Firevette

These are from memory...(I cant find the timeslips)

Previous best 8.89 @ 78 (1.9 60') was consisant in the low 8.90's
After intake 8.78 @ 79 (1.9 60') now consitant in the high 8.79's

So only a gain of 1 mph and after thinking about it is more like .1-1.5 faster.

GREGGPENN

I suppose I should have spoken to the issue of runner length. I forgot.

I understand the length of the runners controls the dynamics of cylinder filling and when optimum power occurs. Though the physical diameter of the head/base/runner ports seem to be sized to flow equally, the dynamics of the motor can be changed by altering the runner length. Specifically low-end power can be traded for higher revving. Shortening the runners might result in lower trap speeds though the car could actually "feel" slower.

In past threads I've seen posts by several modders who say they'd never mod an L98 (except for the exhaust) w/o doing the whole motor. This is the purpose of this thread -- to see how well that statement really holds up.

CFI-EFI

???



Let me see if I understand what you are saying.

From your second sentence:
200 cfm @ 28" Heads.
200 cfm @ 28" Base.
200 cfm @ 28" Runners.
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-----------84" of water?

Are you getting 84" of water from the three measurements, heads, base, and runners? What if you throw in the flow of the TB? Will that raise the pressure drop to 112"? If the heads flow 200 cfm and the base flows 200 cfm, and the runners flow 200 cfm, does that make for a flow of 600 cfm? Again, what of you factor in the TB? Am I reading you correctly?

RACE ON!!!

dan0617

Ported 113's and bigger valves go hand in hand from what I've found by many hours of searching and flow numbers. Can't do one without the other. Ported and bigger valved 113's seem to flow really well from .100 to .400 lift, and mediocre at .500 and above. Most flow 235 to 240 or so CFM at .500. They seem to maintain good velocity at low lift. Best with cams with a .550 or less max lift. From researching, it seems these heads would be best used with a highly modified TPI or a superram, and a moderate cam. Aftermarket 195CC heads, or even 180CC AFR's need a superram at minimum, or a LT1 or miniram intake, with a pretty big cam and can handle big cubes. So, IMO, totally worked over 113's are good for a 350 or mild street 383. A race 383 or bigger engine would need more than 113's or a TPI can give and would be a restriction, no matter what you do to them. Again, this is my opinion. I did not run major mathematical calculations on anything to come to these conclusions. I could be totally wrong. I'll know I'm wrong if I get my car together this winter with worked over 113's and it runs like crap!!

davenbocafl

I use to hold the national record in F/G NHRA in a 63 split window corvette. I can tell you the intake that was on my 86 should have been on a 6 cylinder, Ex is OK @ 1&5/8's but shoud have been 1& 3/4. On my 86 I replaced the TPI with an Eldlebrock street performer ( idle to 5500) and a 750 Holley Vaccuum Sec. and electric chock, kept the cats (for green) but eliminated smog pump and pulling about 350hp and 350torgue
and 22 mpg. oh also changed my rockers to rollers 1.6

GREGGPENN

I've never seen anyone claim to get 350HP out of a stock 350 simply by changing intake and rockers.... By your wording, you've gotten a stock motor producing less than 250HP up to 350 with those two changes. That's not consistent with anything I've ever read here.

CFI-EFI:
I don't recall the specfics but I understood the iron heads (@40lbs heavier) to actually produce better power -- though not necessarily enough to offset their extra weight (maybe after porting?). That could be bogus since I wasn't really interested in figuring out if I'd want older heads on my '89. Please correct me on the reason (if any) on why they're different. I was thinking there was a small diff in cc.

I'll admit I'm uncertain if the change to lighter 113 heads was an overall improvement vs prior iron heads, but I'm under the impression the difference isn't enough to change what the intake requirements should be.

Dan0617:
You didn't directly answer my post though you quoted it. Thanks for the extra opinions on the potential of the 113s. But, this thread is drifting from the main point which is:

Can the stock intake adequately feed the stock motor. I've seen many posts complaining about the intake, why it's choking motor, how it was intended for a 305ci, etc... But, I haven't seen anyone really show why! In comparison, there weren't factual numbers to show why exhaust mods would work -- so I just had to try. The intake is different though. Numbers are there and I don't see the advantage. I'd like someone to enlighten me -- if I'm wrong.

I do note that timeslips for the intake change on 65Z01's website show the equivalent of a 10hp gain with an intake change -- but that was on a modded motor! TPIS claims 15hp on their big mouth and Accel about the same. People say I should buy a used version to save money cause it's a better value. (My thought is buying a used manifold could require planing to make sure it's straight before installation. By the time I do that, why bother? Moreover, why bother if I don't do heads/cam?)

gp

Steve85

Yes, because the motor is a package and when GM looks at what a TPI intake is capable of, it makes no sense to go with 300+cfm heads and 242 solid roller with .630 lift. The rest of the package is compromised to suit the capabilities of the intake.

Throw on a diff't intake and all of the sudden the 350 is capable of so much more.

So...again yes the tpi is enough for the stock motor but only because it is a self fulfilling prophecy (if you will). With diff't heads cam etc, the tpi is not enough for a 350.

lite blue

I'd always read that the TPI was sized for the LB9 (305) motor, and was a restriction on the L98. Don't know if that is fact, but it sure gets repeated a lot.

tpivette

personally, i think the stock heads/cam combo are more restrictive than the intake setup... which is why you see very little gain from upgrading the TPI peices on a stock motor

everyone seems to replace the intake peices before heads and cam... id like to see it happen the other way around just for fun, and to see if im correct. anyone wanna throw a mild head/cam package on a stock TPI intake equipped L98?

GREGGPENN

Everyone trying to sell upgrades to the TPI setups quotes this! I have to think it must be slightly oversized for the 305?

And, speaking back to my initial comments about the limitations of the overlooked plenum, look at this pic I took....


Note the many blockages of the TB openings.
1) The humps at the bottom (though slightly set back) block the lower flow at WOT. (These are often removed).
2) The sides are narrower than the opening. Not much I can see to cure this.
3) The side humps (as shown on the left) are the humps that block a more direct flow in the runners which bolt to the sides. They can be ground down or removed in a siamese fashion. (See the CorvettePlenum website to get a better idea of what I mean).

gp