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Alpine engine power limitations


Diamond Level Sponsor
So WHAT is the problem with an Alpine engine?

My recent research seems to change the question to: What isn't the problem?

I have been scratching my head over WHY the Alpine engine runs so poorly,

compared with a small block Ford V8, with similar modifications.

Now, the early small block Ford (in stock form ) is not known for it's outstanding specific power output

But with the right parts, it does OK. And, of course, it benefits from DECADES of use and Hot Rodding.

The Alpine engines I have played with don't respond the same with similar parts.

The big indicator is camshafts.

In general, the smaller the engine displacement, the less cam required for the same level of performance.

The Alpine engines that I have installed comparatively large cams don't respond as they should, WHY not?

Of course, it has everything to do with air flow.

The Alpine head has historically been suspect of low flow, with the exhaust ports the main culprits.

Recently I was talking to an experienced head guy, and to my surprise, he was NOT all that concerned about the exhaust ports. He admitted they were not great BUT he thought the problem could be handled within the given space and, mostly, with the proper cam timing.

The head guy was not thrilled with the intake side of the head. He IS a Big proponent of Intake flow!

This was a surprise to me! I always thought the intake tract was OK. It has a "text book" correct shape and few imperfections.

However, comparing the SIZE of the intake port with other engines, it could be bigger.

One engine I recently used for comparison, was the GM Ecotec engine 2.0 L turbo (Gen 2 LNF), at 2.1 HP/CI
One thing NOT a problem in spite of the turbo, is intake port sizes!

If the engine was going to be force fed, why such big intake ports?

With this different path to research, I dusted off the old computer program "Desktop Dyno 2000".

I have played with the computer program in the past to see how to INCREASE the power,

This time I went to the program to see what is LIMITING the POWER.

In the past, the Dyno program didn't compare to reality. It had much more power at the higher RPMs than the engine produced.

This time, I started with the intake tract.

I already had plugged in numbers for everything including the dismal head port flow from past use.

Low and below, when I cut back the CFM of the carburetion, the Dyno results started to look like the real world I am seeing!

Remember, this is the same bad ports, just a change in carburetion!

So I compared the intake world of the small block Ford to the Alpine.

With the Ford, it truly is unlimited! You can bolt on a LOT of CFM!

However, it looks like 10 CFM /CI will yield 1.5 HP/CI.

When looking at the Alpine, using 40mm Webers with 30mm chokes, it's looking like it only sees 6 CFM per CI!

I now have a new view point to work with.

Gee, maybe the sage head guy is RIGHT!
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Diamond Level Sponsor
This info from the Z world sheds some light on the problem.

If I'm looking for 200+ cfm per cylinder, the 40s are not going to cut it.

Of course, getting air thru the carbs is one thing, getting it into the engine is another....

Venturi Size & Airflow.jpg


Donation Time

Carl Christiansen iirc was a big proponent for the rare 42dcoe.

Ill drop you an email in the next few days re some work a fellow alpine racer did when he was suffering restriction in his motor and they ported out the choke tubes bit by bit till they gained their HP..


Diamond Level Sponsor
MK, I talked to the Sage head guy about the 34mm Weber chokes

and he pointed out that he has seen flow increases with a back cut on the choke tube.

I may do that mod, after testing the chokes as they are.

But I'm now going to start looking for some 45mm Weber carbs.
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Gold Level Sponsor

I had Mike Pierce of Pierce Manifold rebuilt my Webers this winter and the results were terrific. Still successfully running Carl C.'s engine after rebuild, more power than ever. I am using the original DCOE 40 webers (special for Alpines) with 36 mm chokes. Mike Pierce told me to run 34mm chokes and I would have faster laps at a track like Lagua Seca. I'll send an email tonight,



Diamond Level Sponsor
So I started the feasibility study for changing the chokes in the Weekend Racer Alpine from 30 to 34.

So the first question is: did I get the correct parts?

Comparing them to the chokes from the old 34&35 Carbs, I'm wondering!

The new chokes have a different lead-in compared to the 30s.

The exit diameter of the Aux Venturi is 37mm (no wonder why 36MM chokes are diminishing returns in a 40),

the old 30s have a shoulder to mate up to the Aux Venturi, but the new chokes do not have the same shoulder.

Hmmmm, Looks like I may need to start a thread about Modifying 40 DCOEs to Flow MORE...

We'll see after I test the 34mm chokes....IF it's a valid test...I'm not thrilled with the step from the Aux to the choke...

....AND the rest of the flow limits found in the 40 DCOEs

I have not looked close at the 151s to see if there are differences with the old carbs as far as Aux Venturis flow possibilities.

AND, it looks like there is improvement in flow to be had just by removing the casting seams in the Aux Venturis!

The 45 DCOEs are looking better!

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Bronze Level Sponsor
There is something about the way the air will "swirl" in the intake runners. Look at the GM Quad4 intake manifold runners, they are not circular at all. Look at the LS intake ports and they are very rectangular.


Diamond Level Sponsor
The jury is almost in on the 34mm chokes.

I say almost because my test yesterday was foiled.

So I didn't get to do a full test.

But what little bit of testing I did do is VERY encouraging!!!

As the sun was sinking lower, I buttoned up the choke change and knew I needed to change to some bigger main jets.

I was running the 30mm chokes with 110 mains and they were a touch on the lean side.

So I looked thru my likely available mains.


I stuck in the 135s and lit it up for the test.

I was very surprised how well it ran!

With slow, light throttle, NO PROBLEM!

After running the Track event last weekend, the car still had the open exhaust straight pipe.

So I gingerly made my way out of the residential area, I tried to determine the jetting without making too much noise.

The good news is it seemed to NOT be too lean.

Imagine my disgust when I found the road CLOSED!

So I turned around and gave it a blast!

The bad news is I could only watch one thing at a time, the Tach or the A/R gauge.

I chose the Tach.

For the FIRST time, the engine actually PULLED up to 6000 RPM!

AND it was still PULLING when I shut it down!

At this point, I'm VERY hopeful about the direction things are going!

More testing today!


Donation Time

What was the jetting you were running on track? You weren't running 110 mains in it on the track before surely? ..


Diamond Level Sponsor
Yes, I was running the 110 mains. BUT Willow is at about 2200 FT so it's not so bad.

If I ran at sea level, I would be TOO lean.

IF I planned to keep the 30mm chokes, I would fine tune it better, BUT I knew I wanted to go bigger on the chokes

And likely needing different jets.



Platinum Level Sponsor
I hope you don't mind me jumping in with a question; What keeps the Alpine engine from revving (outside of stock rods)? My Spitfire, back in the day, would easily run 7k to 7500 with 3 main bearings. Kasner was rumored to be able to go to 8K if he had to. Judging by the speed his cars went by me I believe it. The Midgets and MGB's would also run about the same RPM's.
Does the Alpine breath poorly or is it a long throw engine.
Thanks, just curious. Interesting thread BTW.


Diamond Level Sponsor
So I put on the muffler and did some more street testing.

I found the 135 mains were too rich at the high rpms, but still lean in the mid rpms.

Street drive-ability was quite good with only a small flat spot off idle.

If I didn't have the wideband, I would have no clue how lean the midrange driving was (16-17).

I was amazed how well it ran being that lean!

I changed the mains down to 125. this brought the high rpm A/F into a reasonable range without changing anything else.

I ordered some 130 mains, to take to the track.

The bottom line of this testing is that the 34mm chokes did NOT hinder street driving,

BUT the fuel curve was right on the ragged edge of too lean,

that you would expect with over sized chokes.

I expect the fuel curve could be improved, but I want to make some changes to the carbs

(mod the aux venturi and back cut the chokes), before putting the time into fine tuning the A/F.

As far as POWER, the bigger chokes are NOT the silver bullet I had hoped for, but an incremental improvement, with no significant down side.


Diamond Level Sponsor
I hope you don't mind me jumping in with a question; What keeps the Alpine engine from revving (outside of stock rods)? My Spitfire, back in the day, would easily run 7k to 7500 with 3 main bearings. Kasner was rumored to be able to go to 8K if he had to. Judging by the speed his cars went by me I believe it. The Midgets and MGB's would also run about the same RPM's.
Does the Alpine breath poorly or is it a long throw engine.
Thanks, just curious. Interesting thread BTW.

The factory 1725 engine is close to "square" with a bore of 3.21" and a stroke of 3.25" and the stroke (same as a 327 Chevy) is certainly not a limiting factor.

One issue is that factory Series Alpine engines have heavy reciprocating components. It has been documented here that replacing the factory rods, pistons and wrist pins with more modern (not modern, just stock 1960's Chevy rods / wrist pins and comparable pistons) components reduced the total reciprocating weight by over 1200 grams which means that the factory 1725 parts were ridiculously heavy.

It has also been noted here that the factory exhaust port design is very poor which limits the ability of the engine to breathe at high RPM.
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Jay Laifman

Donation Time
I am very much appreciating all the work that Dan is doing and sharing.

I can add that years ago Jarrid said that the 1600 crank was lighter than the 1725 and therefore preferred for racing. So that jives with what Barry just said.


Diamond Level Sponsor
More parts of the puzzle are falling into place.

Or I should say, the work NEEDED is becoming clearer.

...With the right hand not knowing what the left hand is looking at...

I have started looking at the Carbs, but that is only part of it.

Even IF I get up to my desired 200+ CFM/port of Carbs, I still only

have Intake port flow of less than 170 CFM ish.

See the head flow thread:


So the current goals are:

-- Head flow increase, BOTH intake and Exhaust.

Bigger Ports and valves, CNC port work.

lighter, Smaller stem valves.

-- Higher flow Carbs

Mod 40s or jump to 45s

-- Faster/higher valve movement.

1.6 rockers.

-- cam with More overlap

106 or less LC. I may have to test a Holbay cam with 103 LC.

-- Higher flow Exhaust.

Test the Atalla Tri-Y, with an improved collector.

Test a 4 into 1 Header.

Pan evac system.

-- And last, but not least, BIG compression.

Big time Head milling with flat top pistons.

Dry deck head gasket surface.

...just a little bit of a Christmas list going here...

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Diamond Level Sponsor
In reviewing this thread, I want to make some things clear.

In the OP, I stated in the small block Ford world, 10 CFM/CI would yield

1.5 HP/CI.

It's Very easy to look at that statement and say I'm NUTS!

That would mean a 289 CI engine would NEED 2890 CFM to make 433 HP.

Everyone knows you can make a LOT of power with a LOT smaller carb than 2890 cfm.

HOWEVER, when you talk about individual runner carbs, things change.

In the case of the 289 Ford, It's NOT uncommon to see a Vintage Race Cobra

running a "289" engine with 48 IDA Webers sporting 45mm chokes!

Some people suggest a 48 IDA Weber, with 45mm chokes, will

flow 700+ CFM (2 barrel x 4 = 2800).

And those same people will tell you they can make MORE power

with a NON individual runner intake system,

a single plane intake manifold with a Holley 750 CFM.

In reviewing some Weber info, I found a recommendation to use 42mm chokes on

a 1600cc engine running 8000 RPM, OH Boy!

So, if you are thinking about that formula that suggests you only

NEED X CFM for a Y sized engine, give it up! NOT the case with IR Webers.

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Diamond Level Sponsor
Above is mentioned modifying the 40mm carbs or jumping to 45s,

Here is link about Modifying the 40s and jumping to 45s.

If you are using 40mm DCOE Webers, with 30mm chokes, you are leaving power on the table.