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Head/Cam/Carb Combo Questions for a Bus Engine Build
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Tusk
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PostPosted: Wed Jun 09, 2021 8:27 am    Post subject: Head/Cam/Carb Combo Questions for a Bus Engine Build Reply with quote

Hello all!
My buddy and I want to build a motor for his '61 Splitty (no RGBs)
We already have a machined case and are pretty set on building a 1641 as the cylinder spigots are not bored for anything larger.
But we've got some concerns on the head, cam and carb combo...
We have some brandy-dandy new big valve DP heads from AA on the shelf, and we were considering a CB cheater cam, but because of funding were probably going to stick with a single Solex 34/3. The concern here is that the carb won't be enough for those heads and that cam.

I called CB, because I haven't been able to get AA to answer the phone or emails for three months now, and the gal on the phone said that this setup should be fine though without really knowing anything about AA's heads, she couldn't say for certain...

Which brings me here! What say you? Is this setup useless? What do ya'll suggest?

This Bus will be daily driven and I know he'd like to be able to charge up hills and at least do 70 on the highway. Again, the RGBs have been removed and (so we're told) a '68 Beetle swing axle was put in.

Thanks in advance,
/T.
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Dan Ruddock
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PostPosted: Wed Jun 09, 2021 9:04 am    Post subject: Re: Head/Cam/Carb Combo Questions for a Bus Engine Build Reply with quote

Tusk wrote:
Hello all!
My buddy and I want to build a motor for his '61 Splitty (no RGBs)
We already have a machined case and are pretty set on building a 1641 as the cylinder spigots are not bored for anything larger.
But we've got some concerns on the head, cam and carb combo...
We have some brandy-dandy new big valve DP heads from AA on the shelf, and we were considering a CB cheater cam, but because of funding were probably going to stick with a single Solex 34/3. The concern here is that the carb won't be enough for those heads and that cam.

I called CB, because I haven't been able to get AA to answer the phone or emails for three months now, and the gal on the phone said that this setup should be fine though without really knowing anything about AA's heads, she couldn't say for certain...

Which brings me here! What say you? Is this setup useless? What do ya'll suggest?

This Bus will be daily driven and I know he'd like to be able to charge up hills and at least do 70 on the highway. Again, the RGBs have been removed and (so we're told) a '68 Beetle swing axle was put in.

Thanks in advance,
/T.

It would work better with stock valve heads.
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Brian_e
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PostPosted: Wed Jun 09, 2021 9:14 am    Post subject: Re: Head/Cam/Carb Combo Questions for a Bus Engine Build Reply with quote

Sorry ..... but I can't think of a much worse combo for a bus without reduction boxes. d'oh!

If you refuse to bore the case, sell/trade the big valve heads for some correctly ported stock valve heads. Ditch the slip-in egg shell 87's, and run some thick wall 88's. They will go in the stock case bores, but you will need to get the heads bored.

Run the cheater cam with the stock carb, 1 3/8" header, and 8.0-8.3cr, and a tight deck height.

Even better, just make it a 1776cc with all the other parts the same and it will be about the perfect small, stock carb bus engine.

Out of the box "Big valve" heads flow worse than slightly cleaned up stock valve heads. I have tested them on my flowbench many times, and they have some terrible choke issues just under .400" lift.

Brian
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Tusk
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PostPosted: Wed Jun 09, 2021 9:45 am    Post subject: Re: Head/Cam/Carb Combo Questions for a Bus Engine Build Reply with quote

Dan Ruddock wrote:
Tusk wrote:
Hello all!
My buddy and I want to build a motor for his '61 Splitty (no RGBs)
We already have a machined case and are pretty set on building a 1641 as the cylinder spigots are not bored for anything larger.
But we've got some concerns on the head, cam and carb combo...
We have some brandy-dandy new big valve DP heads from AA on the shelf, and we were considering a CB cheater cam, but because of funding were probably going to stick with a single Solex 34/3. The concern here is that the carb won't be enough for those heads and that cam.

I called CB, because I haven't been able to get AA to answer the phone or emails for three months now, and the gal on the phone said that this setup should be fine though without really knowing anything about AA's heads, she couldn't say for certain...

Which brings me here! What say you? Is this setup useless? What do ya'll suggest?

This Bus will be daily driven and I know he'd like to be able to charge up hills and at least do 70 on the highway. Again, the RGBs have been removed and (so we're told) a '68 Beetle swing axle was put in.

Thanks in advance,
/T.

It would work better with stock valve heads.


That's what I was thinking too, but wanted to be sure. He isn't necessarily dead set to a single carb. With the big valve heads, do you think a set of dual 34 Solexs would make a difference? Or then does it become not enough displacement for the heads and carbs?
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Tusk
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PostPosted: Wed Jun 09, 2021 9:58 am    Post subject: Re: Head/Cam/Carb Combo Questions for a Bus Engine Build Reply with quote

Brian_e wrote:
Sorry ..... but I can't think of a much worse combo for a bus without reduction boxes. d'oh!

If you refuse to bore the case, sell/trade the big valve heads for some correctly ported stock valve heads. Ditch the slip-in egg shell 87's, and run some thick wall 88's. They will go in the stock case bores, but you will need to get the heads bored.

Run the cheater cam with the stock carb, 1 3/8" header, and 8.0-8.3cr, and a tight deck height.

Even better, just make it a 1776cc with all the other parts the same and it will be about the perfect small, stock carb bus engine.

Out of the box "Big valve" heads flow worse than slightly cleaned up stock valve heads. I have tested them on my flowbench many times, and they have some terrible choke issues just under .400" lift.

Brian


Forgot to mention we're going to run a Vintage Speed Super Flow exhaust on it. We're not really in a position time and money wise right now to bore the case out for 1776; he'd like to have the Bus running and driving by July 17th and the nose is cut out, interior gutted, and paint stripped. I know quickest easiest route here would be to just build a 1641DP would a single carb and stock cam, but I figured if we're gonna be in there anyway, what else can we do? Hypothetically, if the big valve heads didn't flow like shit, would a set of dual carbs play better with those heads and that cam or is it not enough displacement?
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Clatter
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PostPosted: Wed Jun 09, 2021 10:14 am    Post subject: Re: Head/Cam/Carb Combo Questions for a Bus Engine Build Reply with quote

Doing 70 on the highway in a bus with thin-wall 87s..
It'll happen (maybe), but not for very long.

A bus motor is best built with a careful eye to details and the right combo.
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Brian_e
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PostPosted: Wed Jun 09, 2021 10:24 am    Post subject: Re: Head/Cam/Carb Combo Questions for a Bus Engine Build Reply with quote

Tusk wrote:

Forgot to mention we're going to run a Vintage Speed Super Flow exhaust on it. We're not really in a position time and money wise right now to bore the case out for 1776; he'd like to have the Bus running and driving by July 17th and the nose is cut out, interior gutted, and paint stripped. I know quickest easiest route here would be to just build a 1641DP would a single carb and stock cam, but I figured if we're gonna be in there anyway, what else can we do? Hypothetically, if the big valve heads didn't flow like shit, would a set of dual carbs play better with those heads and that cam or is it not enough displacement?


The smallest VSpeed muffler will be fine. When you are building an engine for a bus, you need to keep things mild and focus on low end torque. Low end torque comes from airspeed in the heads. Big valves with bad ports are airspeed killers.

Stock heads with the bowls blended, and good 3+ angle valve job will be plenty for what you need. I have posted this lots before, but here it is again. Quick easy 18+ cfm on stock heads.

https://www.thesamba.com/vw/forum/viewtopic.php?t=682243&highlight=

I showed a single port, but the dual port valve bowls are the same, and the gains are very similar.

If you don't want the thick wall 88's, then just stick with stock 85's. I only got 5000 miles out of a set of slip-in 87's before they were so warped the rings wouldn't seal. That was in a bug.

Any dual carbs correctly set-up on a 1600-1679 will most likely run better than a stock carb. When you start getting the displacement up, then the small single barrels are the limit.

Building an engine with a deadline is never a good idea. Cutting corners to save time just to make an event will most likely result in burning money and time, and having to do it all over again. I have built a bunch of successful engines, I have all my own machine tools, and it still takes me a month of evenings to get one together, and the cam break-in done. That doesn't include install and make sure the rest of the bus is road worthy.

Brian
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PostPosted: Wed Jun 09, 2021 10:25 am    Post subject: Re: Head/Cam/Carb Combo Questions for a Bus Engine Build Reply with quote

Just build it stock if you can't put more time in money into building a well thought out performance motor.

If you don't do it right (with a lot of thought, time, care, and workable budget) it will run shittier and have more problems down the road than a stock one would.

Theres no way he will have it done in a month if the car is stripped and there's no engine, That's what they call "slapping it together."
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chrisflstf
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PostPosted: Wed Jun 09, 2021 10:31 am    Post subject: Re: Head/Cam/Carb Combo Questions for a Bus Engine Build Reply with quote

As a bus owner, I would strongly advise following Brians advice. He has the experience and data to know what works well. You dont need big valves.
A straight axle in a bus with a small motor isnt a good combo either
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Tusk
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PostPosted: Wed Jun 09, 2021 11:19 am    Post subject: Re: Head/Cam/Carb Combo Questions for a Bus Engine Build Reply with quote

chrisflstf wrote:
As a bus owner, I would strongly advise following Brians advice. He has the experience and data to know what works well. You dont need big valves.
A straight axle in a bus with a small motor isnt a good combo either


What makes the straight axle/small motor combo so bad for a Bus? We drove this toilet home to Massachusetts from Minnesota and didn't have any issues. It also didn't have cylinder deflector tins on it; we bought it like that. Picked it up at the airport and immediately drove home. That part I know is bad, I've been harping on him to do something about it since he bought it.
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PostPosted: Wed Jun 09, 2021 12:46 pm    Post subject: Re: Head/Cam/Carb Combo Questions for a Bus Engine Build Reply with quote

Tusk wrote:
chrisflstf wrote:
As a bus owner, I would strongly advise following Brians advice. He has the experience and data to know what works well. You dont need big valves.
A straight axle in a bus with a small motor isnt a good combo either


What makes the straight axle/small motor combo so bad for a Bus? We drove this toilet home to Massachusetts from Minnesota and didn't have any issues. It also didn't have cylinder deflector tins on it; we bought it like that. Picked it up at the airport and immediately drove home. That part I know is bad, I've been harping on him to do something about it since he bought it.


first, follow Brian's advice for the engine build

second, a stock motor doesn't care if its behind a straight axle or a stock reduction box axle, so long as the gearing and tire size is chosen correctly. the PROBLEM is that many people with straight axles install too-tall gearing and tires for the small engine to push happily. Choose appropriately, and a stock 1600 dual port can cruise 65-70 all day long in a lowered bus.
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PostPosted: Wed Jun 09, 2021 1:00 pm    Post subject: Re: Head/Cam/Carb Combo Questions for a Bus Engine Build Reply with quote

Busses in general are/were underpowered from the beginning... The "lucky" part is, that the splitbhus is actually not that hard to push through the air. But, with which succes depends a great deal on what transmission was used for the straight axle swop. A 4,375 and a nice 1600 will do the job nicely. A 4,125 and it will soon loose its arm on even small hills. A 3,88 slightly worse again. If/ when the engine is out the easy way to figure out what final ratio you have is to lock one wheel, put it in 4rth, turn the inputshaft 100 turns and have another person count the revolutionbs the other wheel is taking and then calculate bacwards.
A purpose built 1600 will do the job nicely if youre not in a hurry, even with a 4,125 transmission, as long as youre understood with having to downshift even on smaller grades.
A nicely designed 1600 engine will soon pull 15-20% more torque than a stocker, also through a 34 Solex. And while thatīs not a lot in real life power it does make a significant difference in the driving experience.

I agree with the rest. 87 mm barrels are not the solution on a bus engine. I would also rather stay at stock 85,5 and bump the compression instead. - or go larger on the displacement like 90,5 bore. A 1776 with a nice cam like the CB 2280 or the 2232 can make for a nice engine for a bus, even with a slightly modified stock carb.

- Ohh, Iīm basicly repeating what Brian wrote up north. Ahh well, Heīs right Smile
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PostPosted: Wed Jun 09, 2021 1:22 pm    Post subject: Re: Head/Cam/Carb Combo Questions for a Bus Engine Build Reply with quote

Alstrup wrote:
Busses in general are/were underpowered from the beginning... The "lucky" part is, that the splitbhus is actually not that hard to push through the air. But, with which succes depends a great deal on what transmission was used for the straight axle swop. A 4,375 and a nice 1600 will do the job nicely. A 4,125 and it will soon loose its arm on even small hills. A 3,88 slightly worse again. If/ when the engine is out the easy way to figure out what final ratio you have is to lock one wheel, put it in 4rth, turn the inputshaft 100 turns and have another person count the revolutionbs the other wheel is taking and then calculate bacwards.
A purpose built 1600 will do the job nicely if youre not in a hurry, even with a 4,125 transmission, as long as youre understood with having to downshift even on smaller grades.
A nicely designed 1600 engine will soon pull 15-20% more torque than a stocker, also through a 34 Solex. And while thatīs not a lot in real life power it does make a significant difference in the driving experience.

I agree with the rest. 87 mm barrels are not the solution on a bus engine. I would also rather stay at stock 85,5 and bump the compression instead. - or go larger on the displacement like 90,5 bore. A 1776 with a nice cam like the CB 2280 or the 2232 can make for a nice engine for a bus, even with a slightly modified stock carb.

- Ohh, Iīm basicly repeating what Brian wrote up north. Ahh well, Heīs right Smile


I'll have a look at the trans next time I'm underneath. I've been convinced to dial back to stock heads and stick with 85.5 jugs. But what of the cam? Is it still worth putting a Cb Cheater in?
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PostPosted: Wed Jun 09, 2021 1:34 pm    Post subject: Re: Head/Cam/Carb Combo Questions for a Bus Engine Build Reply with quote

Yes its worth it, and make sure the compression is at least 8.0 with a tight deck. Use the cheaper cb1512 lifters.

Little 1600's more than anything....all the little details start to add up.

Also, don't underestimate the benefits of spending 15min per head blending the valve bowls, and have your local engine shop do a REAL 3angle valve job on them.

Brian
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PostPosted: Wed Jun 09, 2021 3:12 pm    Post subject: Re: Head/Cam/Carb Combo Questions for a Bus Engine Build Reply with quote

Just to show what a little TLC can do along with being meticules with a stock engine.
Here is a 1600 type 1 i built some years back for a ī72 convertible.
Totally stock internals apart from my standard balance job, along with rods lightened 30 grams along with 356 piston squirters and the balancing.
Case decked for 1,05 mm deck height. stock pistons, balanced +/- 0,5 grams.
Cylinderheads cleaned up in the bowl, casting flashes smoothed, rounded off edges in the exhaust, guide boss trimmed. NO MORE. Stock intake valves trimmed (smoothed) on upper side along with a 30 degree cut back. Radius cut on intake seats (Formula Vee style) regular 3 angle on exh. Non plug side of chamber laid back slightly. Cut for 8,2 CR.
1,25 rockers on intake, stock on exhaust.
Stock heater boxes. Stock Leistritz muffler. CSP large ID end pipes. (You canīt do it with the stock mufflers of today)
Rebuilt stock 1600 SVDA distributor set up for 10/30/38 advance. Pertronix coil.
Stock intake. 34 mm Solex with 27,5 mm venturi.
Thatīs basicly it.
Image may have been reduced in size. Click image to view fullscreen.

Here is another 1600 with the CB 2232 cam, nice heads, 8,5 CR. CB Centersection along with a little work in the end castings.
34 Solex with 28 mm venturies. Initially an SVDA distributor, but it had a tendency to ping under load at specific rpms, so I swopped to a CB Black box and programmed my way out of it - without loosing power!
1―" CSP heater boxes and CSP Super comp exhhaust.
Image may have been reduced in size. Click image to view fullscreen.

With this cam in a 1600 the idle is a tad lopey, but with the BB I could improve that significantly, down to it being barely noticeable unless for the trained ear.
With stock heaterboxes and say a VS muffler the power will be around 75 hp and a little over 130 Nm. At least thatīs what I typically see.
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PostPosted: Wed Jun 09, 2021 5:50 pm    Post subject: Re: Head/Cam/Carb Combo Questions for a Bus Engine Build Reply with quote

Brian_e wrote:
Yes its worth it, and make sure the compression is at least 8.0 with a tight deck. Use the cheaper cb1512 lifters.

Little 1600's more than anything....all the little details start to add up.

Also, don't underestimate the benefits of spending 15min per head blending the valve bowls, and have your local engine shop do a REAL 3angle valve job on them.

Brian


So I've some experience building engines, albeit small, early stuff. How does one ensure setting a "tight deck" as you say? I've only ever seen those rings that go on the bottom of the barrel to lower compression.
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PostPosted: Wed Jun 09, 2021 6:09 pm    Post subject: Re: Head/Cam/Carb Combo Questions for a Bus Engine Build Reply with quote

Tusk wrote:
Brian_e wrote:
Yes its worth it, and make sure the compression is at least 8.0 with a tight deck. Use the cheaper cb1512 lifters.

Little 1600's more than anything....all the little details start to add up.

Also, don't underestimate the benefits of spending 15min per head blending the valve bowls, and have your local engine shop do a REAL 3angle valve job on them.

Brian


So I've some experience building engines, albeit small, early stuff. How does one ensure setting a "tight deck" as you say? I've only ever seen those rings that go on the bottom of the barrel to lower compression.


You’ll need to have the bottom (or top) of the cylinders faced to shorten the length a bit. Another option is decking the case. I think machining the cylinders is cheaper if the case deck surface is good.
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