Retro Kenne-bell Dual Quad street build by Jim Weise

By diyauto
( 2 )

11 minute read

Retro Kenne-bell Dual Quad street build 

Compliments of Jim Weise @


Another fun project, just a bit out of the ordinary.

Goal here was to build a nice street piece, with some retro KB parts, namely valve covers and the offy dual quad intake, with a pair of 750 Competition Series AFB's, the customer originally purchased from Kenne-Bell back in the late 70's/early 80's. And we wanted to use a set of exhaust manifolds on the motor, to give it that "bolt on intake package and valve covers" but otherwise stock look.

Boardmember Jerry Shumard and his racing partner have been friends and customers of mine for a number of years. Recently, he picked up a shortblock deal I had on the board, and then we actually re-fitted it with some components he had sitting around.. Namely a set of TA Crower billet rods, and a custom set of JE dished pistons. And topped it off with the KB stuff.

Here's the specs

1976 block with TSP machining and appropriate oil mods.
Stock crank- ground, polished and balanced.
TA/Crower billet rods
JE dished pistons
NOS stock timing cover built in the 90's by Dave Johnson, when he worked for TA- very little use on it.
TA 290-08H cam
1971 661 heads, ported, flowing 270/190- Done locally in CA for Jerry, some years ago.
TA 1.6 ratio roller rockers
Offy dual quad manifold, with TSP modification
Dual Competition Series 750 Carter AFB carbs
Modified stock oil pan
Gessler ported exhaust manifolds

9.5-1 compression

Our original goal was 450-475HP.

I had considered shaving the heads to pick up the compression, but decided against it since I was pretty sure we could reach that goal at 9.5-1, and that ratio with iron heads would be plenty safe for that good CA pump fuel..

Some pictures

Billet rod bottom end.

28CC dished JE pistons, at zero deck, with Fel Pro blues.

Dialed in the 290-08H to 106* ILC

The oil pan was unique.. modified for clearance in the front of the pan, for the bigger Crower rods. Never seen it done like this before, but I like it, simple and effective.

Cleaned up the valvetrain, and set valvespring pressures

This is interesting- never seen it before.. the oblong water passage in this head, is only partially opened- a casting flaw, that got by Q-C at the factory. No big deal, just make sure it's over the front block passages, that are not open. If you put this head on so that passage was over the rear of the block, where most of the water comes up from the block into the heads, and then back thru the heads to the intake, you would end up with cooling issues, that would be very hard to track down. This is very rare, as I have dozens of iron heads on the shelf here, and have never seen this before, but it's something to watch for.

The heads were far from perfect, with the work that was done to them. as you can see here, the exhaust valves have a much higher tip height that the intakes.. all of them were up from the stock spec, the intakes were about 2.125, with the exhausts another .050 higher yet.. typical of work I see coming in, from shops that don't realize how critical the tip height is on a Buick.

Not too tough to see that in this picture..

And with roller rockers, there was concern about the ability of this deal to rpm, but I knew that the cam was easy on the valvetrain, and as long as our rocker geometry was within reason, we could give it a try. Remember I am working with a hodge podge of used parts here, so giving the customer's wallet a break is a factor.. But pushrod lengths have to be right, to get that rocker where it wants to work..

And this ain't it..

That's a mock up with the supplied TA 9.350 length pushrods.. and I didn't have to go to the dyno to know that wasn't going to work. Needed at least .150 shorter ones, and TA doesn't even make them that short. And I don't care for adjustables.. had too many of them loosen in the past, and I have adjustable rockers to work with here.

So off to the parts house to grab the melling catalog, and locate some pushrods that would work.. because of the tip height variation, I selected a 8 at 9.165's and 8 at 9.200..

The shorter ones are 5/16, the longer ones are 3/8 with a neck down for the 5/16 ball, but that's no big deal here.. I show the picture because I know I put all kinds of pics of fancy, expensive stuff up here, but I will "make it work for you" if that's what it takes.

We can live with this geometry.. TA's spec is one thread showing, plus or minus 1 thread..

Took his manifold that we had polished some years ago, did a port match, and added a modified TSP splash shield.

Then worked the divider down on the plenums, to pick up some HP up top.

Added the NOS KB covers..

And rounded it out with the carbs and linkage, Plug wires and looms, and Gessler exhaust manifolds, and some nice ARP bolts.

And off to the dyno we went..

Now, whoever said two carbs were twice the hassle of one, was a smart man. It took quite a bit of work on the primary metering stuff, to get it to do down the road nice, at 20, 30, and 40 HP.. this is due to the fact that these carbs are meant to have just one on the motor, and they are pretty good size, so in a dual carb application, each carb is only opening the throttle half as much.. so primary metering is something you really have to work with on the dyno.

But we got it, and then moved on to the WOT stuff, and after a couple 3 times with the carbs apart to re-jet, I was very happy with the results.

This was only the second motor I have had across the dyno that made 500 HP with manifolds, and by far the mildest.. Those 2 4's are workin!

We tried it with a set of TA headers, and were surprised at how little was gained.. remember, there are no hard and fast rules about gains with headers, and Greg's manifolds do a very decent job of getting out the fumes.

I would surely give up the 20 numbers for that stock exh manifold look.

Here's a vid of that 500 HP pull, on manifolds- sounds neat, very different that thru headers.

Definately going to add this motor to my line up.. 2 4's with an otherwise stock look is very cool, especially with this performance.

Yes, manifold is in fact part of the torque equation here.. it's not uncommon for the dual plane versions of this motor to make 540 torque, with around 500 HP.

Compression ratio at 9.5-1 is a factor.

As is the fact that I cut the divider down on the intake plenums. ON a single carb deal, this typically will trade 10 or so ft lbs for 10 HP farther up in the rpm range.

I suspect, based on previous engines, with dual and single plane manifolds, but of very similar cam/headflow specs to this engine, that the trade off of Torque to HP is actually greater here, with the dual carbs and this manifold.

Since this is a street deal, to be run with regular radials, it has more than enough power to shred those tires, so extending and strengthening the upper rpm range of the motor makes sense. It certainly has the rods and to rev it to 6000 on a consistant basis.

Personally, I like a nice balanced motor. Just kind of stumbled into that with this one, I expected it to make 540 ish torque with the headers.. HP gain with the headers was what I would consider normal, or maybe a little on the light side, but typically we see a whole bunch more torque, headers vs manifolds. It's not uncommon to see that 40 lbs or more.

One thing I like to do, is pull it all the way down to 2800 rpm, to start the test.

Especially on one like this, were I will be supplying the converter for it.

Here is the test from the inside of the control room.

At the top of the rpm range, you can hear the dyno oscillate the rpm a bit, as Superflow doesn't expect you to be testing an engine with this much torque at such a low rpm, to this high an rpm level. Typically one would test from say 2800 to 5200 or so, on a more stock engine - therefore the setting that has to be made to the water brake valve to hold it at 2800 and full throttle, won't allow enough water out at the higher rpm.. Ron mentions this right after the test.

Superflow didn't factor in the wide band of power of our BBB's, in their design. Most motors would not make 423 torque at 2800, yet still make HP to 5800

And here's the numbers from that test

After this, we took the tops off the carbs, and re-jetted for the last time, which produced that 500 HP pull. It is interesting how the fuel curve works in these carbs.. and there is not much we can do about it. I am going to try both dual q-jets as well as dual Holley's on motors like this in the future.

And yes, I did clean the smudge off my camera lense, when I got back to the shop here and started viewing the videos..