High Volume Intake Manifold

[Oldav8tor]

I purchased a Holley NH from Russ Potter that I want to try in my '17 Touring. I'm going to install one of Scott Conger's full-flow valves and was wondering if their might be any advantage to installing a high-volume intake manifold? I also have a Z high compression head but everything else is stock.

Anybody have any experience with a high volume manifold, pro or con?

[Don ellis]

I hope so because I'm building one with the same setup.

[speedytinc]

You will gain in top speed by a noticeable amount. The improved head compression/combustion chamber will add horse power.

[Scott_Conger]

Regarding the intake: So long as the car is equipped with a starter, you'll be fine. Some folks claim improvement, some just say "meh". I will personally be interested in your take on it once installed.

At any rate, the larger volume of the intake makes for a little harder starting if it is a stem-winder as the vapor doesn't maintain its velocity like it does with the smaller diameter of the standard iron intake. Once the air is flowing with the engine running, then everything settles down and is fine.

[Moxie26]

My similar setup starts using the choke on both cold and warm engines

[speedytinc]

Velocity can be an issue & would be on a tired stock motor. With the higher compression comes more "suck" So the velocity issue wont be. You will probably find that your motor will be happier maintaining higher rpm's, but you will have the power to pass that slower stock T crawling up the hill.
Anecdotally: My '14 easily starts every time on 1/4 turn. There is a bit more noticeable effort in cranking as one would expect with higher compression.

[RGould1910]

I noticed improved performance changing from an original cast iron manifold to a Chaffins high volume intake manifold. The car was crank start only and there was no issue starting the car after the change. I ran a Ricardo head and Stipe 250 cam and a straight thru NH carb.

[RajoRacer]

I'll just add that I've installed two on customer's cars and I had to slightly grind it where it interfered with the stock exhaust manifold.

[Oldav8tor]

All good info. I have a "gasp" WOSP 12 volt geared starter which spins the motor like a modern car. I would think that would help maintain intake velocity during starting. Right now I can start on mag and seldom if ever need to use the choke. I'm trying to figure out some ways to do a meaningful before and after comparison. I will report back once I've had the chance to do some evaluation.

[Mike Lebsack-Iowa]

I have a couple of cars that I always hand crank even though they are fitted with electric starters. They have the high volume Chaffins intakes and NH carbs. 2-3 priming cranks and they pop right off. If cold ( below 35degrees F.)I enrich the mixture 1/4 turn and it works real well. Dean Yoder taught me that one!!!!

[TXGOAT2]

My late T has one and it starts easily and runs well. (Warm climate) Low speed torque may be off a little and highway performance improved. My car has stock pistons and head. I don't know what the cam is.

[Norman Kling]

My 26 is all stock except for stipe counter balanced crank and aluminum pistons. Standard bore and stroke and standard high head milled just enough to be smooth to seal the gasket. I found it would start and idle ok but very little power at low end especially on hills. However it really ran good at high speeds. I went back to the standard intake manifold and it improved low speed performance. I haven't tried it, but think a high compression head and perhaps a longer stroke crankshaft combined with the high volume intake manifold would run great.
Norm

[Allan]

Tim, there is a way to verify performance improvements. I run a Z head, Chaffins tour cam and an original early cast iron big bore intake. On a tour in Victoria I was offered the opportunity to run my tourer up on a dyno. First run was standard. Then I fitted the big bore manifold and a straight through Holley NH carburetor. The gain was just over 2 hp. Then I fitted the Z head and the total gain went out to just over 7 hp. The car is completely tractable with these improvements. I have not tried to hand start it.
I have had the same experience with Chaffin's repop alloy manifolds. Twice I have had to relieve the tops of the inlet ends to make it clear the original iron exhaust manifold. One required more than I was comfortable with, but it did fit eventually.

Allan from down under.

[TXGOAT2]

Allan, do you have a chamber volume figure for the Z head?

[Allan]

Sorry Pat, I have never felt the need to measure it. Perhaps we should. It may put to rest the compression ratio increase claims made by the makers but which may not be in accordance of others' experience.

Allan from down under.

[TXGOAT2]

"Compression pressure" might be a more accurate and supportable claim.

[speedytinc]

Allan, do you have a chamber volume figure for the Z head?

Some numbers I have collected.
Combustion chambers on the Z heads vary quite a bit. I speced one @ 223CC's (5.4-1)
Stock high head @302CC's (3.97-1)
High head with hi-dome pistons(4.75-1) 70# compression.
Low head milled 1/8", high dome pistons milled to clear 95# compression.
Results will vary depending on deck & piston height.

[speedytinc]

"Compression pressure" might be a more accurate and supportable claim.

Agreed.
I wish I had taken accurate pressure tests after engines are broke in with various heads.