Does anyone know what the acceptable maximum rev limit is for a 2,332cc motor as installed in Vintage Motorcars Speedster?
Jason
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You will be limited by your valve springs. Since we don't know what springs are being used beyond that they are a single spring, I would stay under 5000 rpm.
Edit to correct typo.
5,000 rpm.
500! The engines are torque monsters.
Seriously though. Pat has already spoken on this: 5500-5800 redline. He may have published a dyno sheet (since he always does?). Why not find that dyno chart and limit yourself to the point of peak horsepower?
Given the way they're built and the builder, it's probably fine to over-rev them a bit, but it's also probably pointless: they're made to mimic a stock small block chevy from 1978.
It's my understanding that the 2.332cc motor has a longer stroke compared to a stock Type 1 VW motor. And the longer stroke results in a higher piston speed, so I thought the maximum rev limit may be something less than 5,000 rpm.
Jason
@JasonC posted:It's my understanding that the 2.332cc motor has a longer stroke compared to a stock Type 1 VW motor. And the longer stroke results in a higher piston speed, so I thought the maximum rev limit may be something less than 5,000 rpm.
Jason
Well.... sorta?
Piston speed is as much a function of connecting rod length as it is of stroke. There is a sweet-spot for what is called "rod-ratio" - high revving engines like a lower numerical rod ratio. A longer (84 mm in the case of a 2332) engine running stock-length connecting rods has a higher rod ratio than a 69 mm stroke (stock) engine running the same rods, so the bigger engine is limited in regards to ultimate RPM.
.... but rod ratios are not the typical RPM limiter in an engine. The bottom end can be built of stout stuff - good crank, strong connecting rods, forged pistons - that allow the engine to safely spin to 7500 RPM and higher. At some point up there, the rod ratio starts to be the limiter, but it's way, way past your redline.
The RPM limiter in an engine will almost always be valve float - the point at which the valve-springs lose control of the valve motion. Bigger, heavier valves require more spring pressure, but more spring pressure requires heavier push-rods, heavier rocker arms, etc. - which in turn requires more valve-spring still. Super-stiff valve-springs tend to wipe out cam lobes. At a minimum, they create a lot of heat. Panchitos come with 40 mm intakes, which are bigger than stock (certainly), but which are by no means "big". Pat is controlling them with single valve-springs.
LI-Rick was asking about valve-springs, because single springs often limit the maximum RPM to 5000. If the valve-train is light enough, and the springs good enough, 6000 RPM is not unheard of - but to be safe, you'd want dual springs (or a more exotic solution) if you plan to rev to 6500 RPM. The accepted folk-lore and common-knowledge "Samba approved" answer is that singles are useless on any engine with more than a 110 cam and 40 mm valves, because you'll want to be shifting by 5000 RPM.
I'd feel OK revving the Panchitos with single springs to 6000, but I'm comfortable with risk. I'd stay under 5500 if I was risk-intolerant. This rev limit wouldn't change if the engine were a 1600 cc pea-shooter or an 86 mm stroke 2387 - because the heads and valve-springs haven't changed. The limit is not the rod-ratio.
Single valve-springs are the limiter.
I was auto crossing a 914 with a killer 2.5L type 4 engine and over rev'd the engine on a course I needed a taller 2nd gear or a shorter 3rd. The engine popped and I heard a terrible clanking from the engine. I thought the worse of course but new it was all my fault. I got home and pulled the right-side valve cover and found the over revving caused a rocker arm to pop off the push rod. I set it straight and kept on running for many years without issue. The type 4 in the car was built by a guy in New England some place at a shop the specialized in Bentley's if you can believe it and also built killer high HP bullet proof type 4 engines, I wish I had kept his info. He would post and advertise in a 914 forum called Pelican parts or something like that. This is back in the mid to late 90's. Man has time gone by.
Re: Panchito rev limits - I bought mine a few years ago when Pat was at CB Performance. They were offered with single springs (rated to 5500 rpm), dual/high rev springs (rated to 6500 rpm), and the VW650 dual springs (rated to 8500 rpm). Obviously there's a tradeoff with every option. I've got the regular dual springs and my top speed shift cutoff is set to 5800 rpm (although I've had it to 6500 several times with no problems).
I was glad to see this post. I had to go looking for info on redline on the 2332. I happened to see Pat’s interview with Greg saying 5500-5800. Having driven mine, it “feels” kind of optimistic. To my feel, the redline feels like it’s just over 5000, but maybe that is just a practical redline.
@Michael Pickett and @Stan Galat so, would anything else need to be changed to switch Panchitos single springs to double? I am unfamiliar with upgrading anything engine. Carbs, venturis and exhaust I “speak,” but not deeper.
I would think I would spend any money first on a Vintage Speed 50mm exhaust (barrel type), and then later, if ever, get to the heads/valve springs. I asked Greg about any first upgrade and he said no point in doing valve porting, but exhaust was a no brained. He recommended sidewinder, but I want to stay closer to stock look.
@Stan Galat, spot on!
There are single springs on the market that can control the valve train to higher rpm, those being JPM Oteva and Dan Ruddock Beehives.
I’ve never used the JPM springs, but I have set up the Beehives in Panchito heads. These are not just a simple swap in a Panchito, as you must change the valve to a traditional 3 groove, unlike the single groove valves that CB uses. Notice they are taller a take a different retainer than a stock style spring. A lash cap goes on to raise the valve stem above the retainer.
Dan reports he has run the Beehives in 42 x 37.5 heads up to 7100 rpm without issue.
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Valve springs are not too hard if you have the tools and match everything else. My engine is a well-massaged 1776 and the higher revs feel healthy on the occasions that I push it. Your engine is a torque monster that would leave me in the dust.
I'd follow your gut and work on other things than the valve train. Ask yourself how often you want to be on the razor's edge of performance. If it isn't the main thing, focus on other stuff that will make you happy.
@LI-Rick posted:@Stan Galat, spot on!
There are single springs on the market that can control the valve train to higher rpm, those being JPM Oteva and Dan Ruddock Beehives.
I’ve never used the JPM springs, but I have set up the Beehives in Panchito heads. These are not just a simple swap in a Panchito, as you must change the valve to a traditional 3 groove, unlike the single groove valves that CB uses. Notice they are taller a take a different retainer than a stock style spring. A lash cap goes on to raise the valve stem above the retainer.
Dan reports he has run the Beehives in 42 x 37.5 heads up to 7100 rpm without issue.
If I EVER get the 2234 in the car, I'll have that same setup.
@Stan Galat posted:If I EVER get the 2234 in the car, I'll have that same setup.
If I ever get my car, I will put these in it! 2287 cc’s of screaming fury! 
@Teammccalla- if you accelerate in 3rd gear you should be able to feel where it stops making 'more' power- of course it will continue running past that point by 500, 600 or even 800 rpm but the point you felt power drop off is where the engine makes 'peak' power and it's redline. You can rev it past there, but using those rpm's on a regular basis will (I predict) just wear out parts prematurely.
Greg told you that there's no benefit to doing any work to the heads because (I'm guessing) the engine won't make much more power without a new camshaft (case has to be split), exhaust and carburetors. Everything is pretty optimal now, and looking for more power by increasing flow in the heads also means the engine will have to rev higher, hence the other parts upgrade.
If you actually go out and try the 3rd gear trick I'm interested in where you think the redline in Pat's/Greg's 2332 is. Please report back as soon as you know!
@ALB posted:@Teammccalla- if you accelerate in 3rd gear you should be able to feel where it stops making 'more' power- of course it will continue running past that point by 500, 600 or even 800 rpm but the point you felt power drop off is where the engine makes 'peak' power and it's redline. ...
If you actually go out and try the 3rd gear trick I'm interested in where you think the redline in Pat's/Greg's 2332 is. Please report back as soon as you know!
The "top it out in 3rd" rule of thumb is great for a car with a 4.12 R&P and probably viable with a 3.88.
With a 3.44 and standard 3rd it can get dicey.
I was in the passenger seat when Cory tried it in my Spyder on a two-lane residential road with no shoulders, and we were well over 80 mph and still climbing steadily when I insisted he cease.
@ALB I tested it in 3rd on about a 4% up-grade. I’d say 4,800. Maybe a touch higher, but that’s “my” redline. 5,000 in shorthand.
I was amused because the speedo was stuck at 82 mph after. Trees…. I restarted the car and GPS worked again. It’s a 3.88 so it was somewhere around 85 at redline?
@Teammccalla posted:@ALB I tested it in 3rd on about a 4% up-grade. I’d say 4,800. Maybe a touch higher, but that’s “my” redline. 5,000 in shorthand.
I was amused because the speedo was stuck at 82 mph after. Trees…. I restarted the car and GPS worked again. It’s a 3.88 so it was somewhere around 85 at redline?
That makes perfect sense, given the specs of the engine.
Some of us who are addicted to power might cluck at such a "pedestrian" power peak - but really, you're going 82 mph in 3rd and the front end will go pretty light around 100.
It sounds like it's pretty much in the sweet-spot for 90% of the world. Greg was brilliant in specing it this way.
Ed, 6500 rpm, stock 3rd, 3.44 is 95mph with 24.2" diameter 195/60R15. Dicey at 100? That's funny.
We use single springs in Vees. Redline is 6500-6700. The valves are tiny(31.5 and 29 I think). They use beehive springs today, which is why the redline is higher than it used to be(6000-6200). They are not Dan Ruddock's. But I bought a set to try(I'm building a spare motor) as springs are 100% free and legal as long as they are single springs.
Valve float is bad. It wears parts and limits how fast an engine can spin. As a result, lots and lots of time and energy have been put in over the years to determine how to get around it.
Wikipedia elegantly states the problem thus in their article on desmodomic valves:
Valve float was analyzed and found to be caused largely by resonance in valve springs that generated oscillating compression waves among coils, much like a Slinky. High speed photography showed that at specific resonant speeds, valve springs were no longer making contact at one or both ends, leaving the valve floating before crashing into the cam on closure.
For this reason, today as many as three concentric valve springs are sometimes nested inside one other; not for more force (the inner ones having no significant spring constant), but to act as snubbers to reduce oscillations in the outer spring.
The springs just couldn't keep the valves from floating unless they were ridiculously overpowered. This is the approach most VW guys take (ridiculously overpowered springs) when trying to turn spin faster RPM.
It's always been a problem. Along the way, dozens of pretty crazy work-arounds were tried in aircraft and racing engines. Motorcycle companies were always on the bleeding edge of technology in production engines.
An early solution to oscillating spring mass was the mousetrap or hairpin spring used on Norton Manx engines. These avoided resonance but were ungainly to locate inside cylinder heads.
Some motorcycle companies went to crazy lengths to get around it. Ducati Motorcycles used (and still uses, for marketing now) desmodromic valves. This system uses no valve-springs at all - the valves are latched to the camshaft and have an arrangement that uses lobes to both open and close the valves.
Metallurgy has come a long way in the last 100 years. Valve-springs were one of the places where the science needed to catch up to everything else, because while all sorts of really great and cool ideas were being employed on the internal combustion engine, the limiter was always valve-control. The solution eventually arrived at works really, really well.
Valve springs that do not resonate are progressive, wound with varying pitch or varying diameter called beehive springs from their shape. The number of active coils in these springs varies during the stroke, the more closely wound coils being on the static end, becoming inactive as the spring compresses or as in the beehive spring, where the small diameter coils at the top are stiffer. Both mechanisms reduce resonance because spring force and its moving mass vary with stroke. This advance in spring design removed valve float, the initial impetus for desmodromic valve drive.
This discussion has given me an impetus to take the new engine off the back burner and try to get it in the car before next season rolls around.
Thanks for the trip down memory lane's rabbit hole.
@DannyP posted:Ed, 6500 rpm, stock 3rd, 3.44 is 95mph with 24.2" diameter 195/60R15. Dicey at 100? That's funny.
We use single springs in Vees. Redline is 6500-6700. The valves are tiny(31.5 and 29 I think). They use beehive springs today, which is why the redline is higher than it used to be(6000-6200). They are not Dan Ruddock's. But I bought a set to try(I'm building a spare motor) as springs are 100% free and legal as long as they are single springs.
My car has 25.4 inch diameter tires. We were doing about 85 on a road where you couldn't see anything that might come from the edges and would have no place to go if they did. Laugh if you want to; I am uncomfortable with that.
Still turning maybe 5000 with a lot of upside left.
Interesting discussion, I feel like mine is certainly loud enough between 4500/5k to just be done with it and shift up and so I rarely get past 4k actually. Of course, it's not my old racer that I'd sometimes bounce off the rev limiter (modern tech ha ha) on a straight right before a downshift coming to a turn...
For the record, I am very much in favor of bouncing it off the rev limiter, where and when it is safe to do so.