this is the link to weiand's site. it shows how to measure intake manifold height. does anyone have a stock intake off the car that they can measure? http://www.holley.com/HiOctn/ProdLin...AMSM/AMSM.html

I guess I get to respond before PaulD does.... he took many of these measurements, while I took others. I've been collecting them, but posting them here is a good idea.

The following is incomplete, so if you have data to add, please do so. And remember that the following only applies to production intake manifolds used on TBI v8 applications. AFAIK, all these intakes are aluminum, and should have a raised snowflake denoting the Winters Foundry, the OEM that originally made the parts for GM.


There are at least four TBI intakes for GM 305/350 (L83, LU5, and LO3/LO5) applications:

1-3. Fcar, Bcar, and C/K lightweight truck which all use a Rochester 220 TBI unit (dual bore cast into a single TBI unit); years included 1988 to as late as 1995.

4. Fcar Crossfire Injection (CFI) intake used on '83-'84 305 (LU5) Fcars (as well as 82, 84 Ycars on the L83 350). There were some minor differences in the 82 vs 84 Ycar CFI intake castings. The main ones was that the 84s got an approx 1" diam round hole to siamese-together some of the runners; the 82 models lacked it. I don't know whether the Fcar CFI intakes were siamesed or not. CFI intakes always used 2 single-bore TBI units.


As below, dimension "A" is from the manifold-to-block flat, above the timing chain cover and the front fence above the lifter valley, to the mounting flat for the TBI. Dimension "B" is similar to "A" except that it is measured at the rear of the manifold (next to the firewall).

When A and B are the same, then the manifold is flat. A is usally not equal to B because most sbc engines are tipped downward at the rear of the engine to align the crank with the driveline (trans, driveshaft).

I believe these are the same dimensions used by Edelbrock and Holley, and the main issue for each (aside from drivetrain alignment) is hood clearance.

==============================================

Fcar (L03), single 2-bore TBI
casting number: xxxxx482 (need to get the rest of the sequence xxxxx)
(also 10166133 ?)
dist hole ID = 1.375 inches
rear base -to- top of dist pad: ?
dimension "A": ?
dimension "B": ?

==============================================

per Fast355, 6/5/2005 post: (The intake) is not like any L03 intake I have seen. In fact I have only seen one other one and it was on a 350 in a box truck.

G20 van (K vin: L05), single 2-bore TBI
casting number: 10166133
Dist. Hole = 1.375"
Rear Base-to-Top Distributer Pad=1.10"
Dimension A= 5 1/8
Dimension B= 5 1/4

==============================================



Bcar (L03/L05), single 2-bore TBI
casting number: 10105143
dist hole ID = 1.75 inches
rear base -to- top of dist pad: ?
dimension "A": ?
dimension "B": ?

==============================================

C/K truck (L03/L05), single 2-bore TBI
casting number: 14102182
dist hole ID = 1.375 inches
rear base -to- top of dist pad: 1.10"
dimension "A": 3 and 3/8"
dimension "B": 5"

==============================================

Fcar (and Ycar) LU5 (and L83) Crossfire
casting number: 14031372 (1982 Ycar model, no siamese windows between runners)
dual 1-bore TBI
dist hole ID = 1.375 inches
rear base -to- top of dist pad: 1.00"
Measurement "A": 3.75"
Measurement "B": 3.75"

==============================================


NOTES: per PaulD, the C/K truck TBI manifold is visually identical to the Bcar manifold except (according to other posts here on ThirdGen) that it is taller. So seanof30306, the info above from the truck manifold should be useful by assuming that the Fcar manifold will be no taller.

I'll assert for now that the Bcar and Fcar manifolds differ only in the size of the hole for the distributor... and of course, they differ in the casting number.

The runners in the non-Crossfire manifolds have very small cross sectional areas and are not radiused in any significant way as the exit the plenum under the TBI. The plenum is also tiny. At some point I'd like to compare them to the runners in the Crossfire manifold.

Based on these comments, these manifolds were obviously not designed for anything resembling performance so it is not a surprise that a 305 can gain sigificant power when replaced by any other manifold and with the appropriate camswap and tuning. OTOH Fast355 has still made decent torque and power using the factory TBI intake on a 350, so it can't be that bad otherwise it would have failed miserably.

The differences between TBI intake and TPI have been beaten to death in many other threads, so I won't relive that here. TPI certainly gains a boost in mid rpm torque, and it looks fancier than TBI, but TPI doesn't appear to give much of a power increase at higher speeds. Both Dyno Don and Fast355 have posted extensively on the TBI vs TPI comparison, and you're welcome to search, read, and decide for yourself.

Finally, I've not seen/heard of anyone doing some mild porting on the stock intake manifold.... though porting should help a lot. PaulD told me that ther water passages inside the manifold might make it more challenging to do the porting.

EDIT: I've done this based on the experience and comments of a neighbor. It does help, but the major work is in siamesing the metal bridge between the bore directly under the TBI --- thatmetal removal will expose the water jacket in the factory intake, so you'll need those holes welded closed. END EDIT.

If you are thinking "Why bother with the stock manifold?", then you might be right if you own a truck or Fcar because you can bolt in just about any aftermarket carb or TBI intake. If you own a Bcar, you can't use the aftermarket intakes as a pure bolt-on because you have to deal with the distributor hole (see the size differences above!). The distributor hole is larger on the Bcars than on F/trucks so that the distributor can be inserted (or removed) in the car without having to remove the manifold. This also means that the distributor is slightly different on the Bcars. The clearance (or lack of clearance) with the cowl in the 91-93 Bcars is the reason for these differences.

Longer than I planned for, HTH.

what i especially need are the heights (front / rear). i have a firebird with a functional cowl induction from an '83 trans am. i have to be able to compare the height of any new intake to the stocker to make sure it'll fit.

Don't know how this got by me k, but as a side point, we may have gotten signals crossed if I said the truck manifold is taller. I believe the truck and B-car manifolds are the same height. Between the two of us, we've never had our hands on an F-body manifold to measure, but I wouldn't be surprised if they were the same height also.

One of the characteristics I'm shopping for in a replacement is lack of 90° bends and runners that require hitting a wall that runs perpendicular to the fuel/air path. All the TBI manifolds I've seen (and most factory manifolds for that matter) require mixture to run smack into a perpendicular wall before transitioning into the head. I'm also steering towards a dual plane manifold. I know one advantage to dual plane does not apply to TBI, namely a strong vacuum signal for carb venturis, but a dual plane should have higher mixture speed at lower RPMs which should lead to better cylinder packing. I'm going towards the Performer RPM because it's a 'bigger' manifold for good flow but still dual plane for good mixture speed.

I know I've told this to kdrolt before, but I figured I'd post it as a FWIW.

Having said all that if anybody wants to buy a TBI manifold with 2" bores let me know.