Enbloc
Part of things
Posts: 353
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Feb 20, 2008 21:41:27 GMT
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Wow, you are right.. that is MADLY overcarbed. A pair of hs2s will flow enough for a mere 80 horsepower! I have absolutely no idea why they chose blatantly incorrect carbs there. The B16 lump used a pair of HS4s, for exactly the same power output. The nice thing about an SU, is it doesn't mind being overcarbed too much, since the venturi is adjustable. There is still no excuse for it though, since getting SUs in the right size is hardly difficult. And it will kill your throttle response. I suppose volvo didn't care about that.. I have to agree and say your theories seem a little off base. My carbs came off a '64 Austin Princess and I can guarantee you that they came from the factory with nowhere near 200 bhp. Rovers came with HS6's as standard for low range drive-ability and fuel consumption. A popular and common mod is to use the HS8's instead which are close to a bolt on. These are seen to have a limitation of just over 200 bhp when fitted to the Rover, which contradicts your 200 bhp starting point for this size of carb. But to say Volvo got there factory fitment WRONG because your A series chart says otherwise is just plain madness!
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Last Edit: Feb 20, 2008 21:43:26 GMT by Enbloc
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Feb 20, 2008 22:40:18 GMT
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to say Volvo got there factory fitment WRONG because your A series chart says otherwise is just plain madness! Agreed. Also, one needs to bear in mind the amount of bullsh!t power figures out there, and even car manufacturers have been guilty of this. To add to the confusion, there's also the differerence between SAE and DIN bhp figures. A specific example of the downright lies regarding bhp figures is that of an A series being used for historic Formula Junior racing, which had been rebuilt and was claimed to be producing 100bhp, but was at the back of the grid. In the quest for more power (& thus better race results), the owner took it somewhere else to be improved. His engine came back to him with a claimed 88bhp, but he was then at the front of the grid!!!! ;D I know which power figures I believe, especially as I also know the guy who prepared it the second time, and he has the dyno charts to prove the power figures that he claimed. However it begs the question of how much (or more accurately how little) power the supposedly 100bhp engine was really producing...... Either way rustybits, I think you've been paying too much attention to the type of people who claimed 100bhp from an engine that was actually producing a fraction of that
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Last Edit: Feb 20, 2008 22:41:29 GMT by Paul H
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Certain Rover P6's... possibly not even the V8... came with twin HD8 (2 inch) carbs. I can't imagine that they would ahve fitted larger carbs than they needed to from factory.
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HD8's are quite rare - came off rover p4/p5's with the 6. As far as i'm aware the rv8's mainly had twin 1 3/4" su's?
Either way you can get a hell of a lot more power out of the humble SU than people think. A local mini tuner has just got 110hp at the wheels of his car with a single HIF44. So that must be nearly cracking 140hp at the crank.
Adding to that, Graeme Russell, Australia's leading A series tuner has got more than 150hp at crank out of twin 1 1/2"s.
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Honestly, I do know my stuff when it comes to the A series. I can tell you for a start, that Volodkovich HAS been listening to the BS merchants I'm afraid. A single HIF44 runs out of puff at 110 horsepower.. At the crank. About 90BHP measured at the wheels. 110 at the wheels is the kind of figure you would get at Baldwin's rollers.
I'm certainly not working off any chart.. Just knowledge of the SU setups used on standard engines, and information about realistic tuned A series specs.
Manufacturers do get things wrong. Surprisingly often. Often, they make decisions for reasons which make sense from a commercial point of view, but not from an engineering point of view. Mind you, that volvo lump is very low compression.. 8.5:1. Lower compression will mean an engine that swallows more air for its power output. It seems they also used twin HD8s on some rather more powerful engines, so perhaps standardisation came into it too. Being mostly spazmatic cars, I don't suppose they fussed much about throttle response either.
Power output is pretty directly linked with the engines air demand. The only major factor is the combustion efficiency. Compression, fuel quality, spark strength, chamber shape, timing, etc.
On a rover v8, the HEADS restrict you to 200bhp. Not the carbs. Replacing the HS6s is not the clever way to get to 200bhp. A good ported head and SD1 cam will do the same, with a much better torque curve. A big carb on an engine with poor breathing may get you a bit more top end power, but at the cost of everything else.
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dalek
Part of things
Posts: 62
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What's the carbs that currently on it ?
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Feb 21, 2008 10:09:37 GMT
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More to the point.. How big are those inlet ports? For the optimum mix of power, torque, economy, and throttle response.. You probably want to match the carb barrel diameter to the port diameter. Those ports look much smaller than 2 inches.
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Feb 21, 2008 11:52:08 GMT
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Honestly, I do know my stuff when it comes to the A series. I can tell you for a start, that Volodkovich HAS been listening to the BS merchants I'm afraid. A single HIF44 runs out of puff at 110 horsepower.. At the crank. About 90BHP measured at the wheels. 110 at the wheels is the kind of figure you would get at Baldwin's rollers. Any crank bhp figures 'measured' at the wheels are at best guesstimates and at worst plain BS (btw, the 88 fly bhp I quote above was actually measured at the crank on a dynamometer in a test cell). I'm certainly not working off any chart.. Just knowledge of the SU setups used on standard engines, and information about realistic tuned A series specs. A series have appalling siamesed porting, so to apply what works on one of those to any other engine is very flawed reasoning . Also I still suspect that a lot of the figures you've been reading are BS. Manufacturers do get things wrong. Surprisingly often. Often, they make decisions for reasons which make sense from a commercial point of view, but not from an engineering point of view. Maybe some do, but just because the spec you see doesn't make sense to you doesn't automatically mean that they are wrong Mind you, that volvo lump is very low compression.. 8.5:1. Lower compression will mean an engine that swallows more air for its power output. It seems they also used twin HD8s on some rather more powerful engines, so perhaps standardisation came into it too. Being mostly spazmatic cars, I don't suppose they fussed much about throttle response either. Where do HD8s come into it? B18 / B20 Amazons with twin SUs had HS6s. And as for this: Wow, you are right.. that is MADLY overcarbed. A pair of hs2s will flow enough for a mere 80 horsepower! I have absolutely no idea why they chose blatantly incorrect carbs there. The B16 lump used a pair of HS4s, for exactly the same power output. if you are saying that a twin SU B18 Amazon has 80bhp, then I suggest you do your research better . Some of what you've been saying does make sense so you obviously have a good deal of knowledge on the subject, but you are also making far too many assumptions that just don't add up.
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Last Edit: Feb 21, 2008 11:53:13 GMT by Paul H
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Feb 21, 2008 12:06:30 GMT
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Honestly, I do know my stuff when it comes to the A series. I can tell you for a start, that Volodkovich HAS been listening to the BS merchants I'm afraid. A single HIF44 runs out of puff at 110 horsepower.. At the crank. About 90BHP measured at the wheels. 110 at the wheels is the kind of figure you would get at Baldwin's rollers. Any crank bhp figures 'measured' at the wheels are at best guesstimates and at worst plain BS (btw, the 88 fly bhp I quote above was actually measured at the crank on a dynamometer in a test cell). Everybody is always having a go at ME for telling them their rolling road figures are over-inflated. They are not wildly inaccurate though, if you ignore the usual "add the coast down losses and a bit extra" method, and simply add on the percentage that the gearbox is known to sap. Somewhere between 15 and 17%. Not perfect, but tends to be close enough, when actually compared with engine dyno figures. Where do HD8s come into it? B18 / B20 Amazons with twin SUs had HS6s. And as for this: I meant to type HS6. My mistake. Wow, you are right.. that is MADLY overcarbed. A pair of hs2s will flow enough for a mere 80 horsepower! I have absolutely no idea why they chose blatantly incorrect carbs there. The B16 lump used a pair of HS4s, for exactly the same power output. if you are saying that a twin SU B18 Amazon has 80bhp, then I suggest you do your research better . www.classicvolvo.com/onlinemanuals/b18_b20_engine/enginespec.htm"80 bhp at 5.000 rpm. (B18D type 1)." That was the lowest figure I could find for a volvo engine with twin HS6 carbs.
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Last Edit: Feb 21, 2008 12:09:46 GMT by rustybits
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Seth
South East
MorrisOxford TriumphMirald HillmanMinx BorgwardIsabellaCombi
Posts: 15,515
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Feb 21, 2008 13:01:15 GMT
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A quick look through some of my info shows that P6 Rover 2000TC's came with a pair of HS8's I doubt they were pushing out much more power than 4ever4's flattie from nearly half the capacity! Single carb models had one HS6.
SU carb sizes really can vary enormously on even the same engine and give different characteristics. On the Farinas with which I'm very familiar the standard carb was a single 1 1/4 HS2 with a needle weaker than the needles in a pair of midget carbs. The result of this I believe is a fast air flow leading to a high torque figure. The MG and Riley 1622's had twin HD4's on almost the same engine resulting in a bit more power higher up the rev range.
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Follow your dreams or you might as well be a vegetable.
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bazzateer
Posted a lot
Imping along sans Vogue
Posts: 3,653
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Feb 21, 2008 13:19:08 GMT
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Being mostly spazmatic cars Perhaps you could elaborate on or explain that comment?
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Last Edit: Feb 21, 2008 13:19:26 GMT by bazzateer
1968 Singer Chamois Sport 1972 Sunbeam Imp Sport 1976 Datsun 260Z 2+2 1998 Peugeot Boxer Pilote motorhome 2003 Rover 75 1.8 Club SE (daily) 2006 MG ZT 190+ (another daily) 2007 BMW 530d Touring M Sport (tow car)
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Feb 21, 2008 13:20:45 GMT
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A quick look through some of my info shows that P6 Rover 2000TC's came with a pair of HS8's I doubt they were pushing out much more power than 4ever4's flattie from nearly half the capacity! Single carb models had one HS6. Ah, thanks for confirming that I wasn't losing my mind! ;D
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Feb 21, 2008 13:54:16 GMT
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Spazmatic = automatic. common enough term I thought?
Anyway, I have looked into the rovers.. And the bog standard 2 litre single carb has a single HS6, for 90 horsepower. The 2000 TC has a PAIR of hs8s.. for just 114 BHP.
Okay, now here is where it gets funny. The 2200 (2.2 litre) single carb, sports a HIF6, with 98 horsies.
And the 2200 TC.. Has a pair of hif6s.. and produces ... 115 horsepower.
So there you go.. the larger, more powerful engine (almost identical in every other specification) has the smaller carbs. Obviously, the HS8s are just a BIT on the big side for the engine..
Also, the single carb rovers back up the estimates I have given for the top end of a 1 3/4" carb on a BMC A series.
Like I have said, overcarbing an engine suffering from breathing problems is a quick way to a bit more top end power, at the cost of torque, fuel economy, and throttle response. Tuners do it.. Manufacturers used to do it now and then.. But it still doesn't make it a good idea!
When it comes to working out what size carbs to use on that old ford.. Guesstimates are the best we have really, since I doubt the conversion has been done much before. Given that 4ever4 wants a good all round solution, I really don't think I am out of line suggesting that HS8s are too big.
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Feb 21, 2008 14:32:27 GMT
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Also, I did a bit more looking up.. The 4 litre rolls engine that pair of HS8s came off, made 175bhp, and sported side exhaust valves, and naff all compression.
The 3.8 S mk2 jag used a pair of HD6s, and made 220 horse, again, showing roughly where the upper limit is for the 1 3/4" SUs.
Since that ford model B (I assume) 3.3 litre engine makes 40-50 horse out of the box, and road tuned ones are about 70 horse, with new head, cam, carb, and manifolds, that is still a long way short of the kind of power range the HS8s are known to cover, unless it is an extremely hot engine of some kind. Obviously, only 4ever4 can tell us what its current power output is.
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Feb 21, 2008 14:42:31 GMT
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I think basing the size of the carbs by what they originally came on, and that specific power output isn't quite the way to go about it. There is no way they'd max out a carb on a production car, or set it up to flow at it's smallest amount. What it boils down to is airflow through the intake, and VE of the engine. If you're searching for the best low end, then sure, it's best to go with smaller carbs, but as far as fuel flow, the needle controls that, as does the needle valve in the bowls. As long as you can keep the bowls full of fuel under Wide-Open-Throttle (can't seem to type W O T here, lol) conditions, then the only thing the size of the carb does is move the powerband up or down. I've seen 1800cc VW engines running a single DCOE 45 with 36mm chokes without issues (not the best combo, but works fine). The variable venturi effect of the SU seems to offer quite a few benefits in regards to flexibility of use, so why not try the big ones.
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1982 VW Rabbit 4-door (apart) 1992 Passat Wagon Syncro (daily)
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Seth
South East
MorrisOxford TriumphMirald HillmanMinx BorgwardIsabellaCombi
Posts: 15,515
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Feb 21, 2008 15:15:30 GMT
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Since that ford model B (I assume) 3.3 litre engine makes 40-50 horse out of the box, and road tuned ones are about 70 horse, with new head, cam, carb, and manifolds, that is still a long way short of the kind of power range the HS8s are known to cover, unless it is an extremely hot engine of some kind. Obviously, only 4ever4 can tell us what its current power output is. 114.3 BHP @ 3910 rpm (98 mph) 188.8 lBft @ 2450 rpm retrorides.proboards86.com/index.cgi?board=general&action=display&thread=1203441315
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Follow your dreams or you might as well be a vegetable.
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Feb 21, 2008 15:38:54 GMT
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There we go then. 114 horse, and torqey with it. HS8s would be right at the bottom end of their flow range, and the bottom end torque would suffer. Not what you want when torque is your engines biggest asset eh? HS6s would be still be in the lower half of their flow range, and definitely not cap the top end. A couple of HS4s would still do it, but be at the top end of their flow range, and probably clip a little bit off the top end power.
So I think HS6s are the sensible option.
Broke 4 speed: Yes, manufacturers frequently do max out the ability of a carb. It is a common way of making sure the engine cant be over-revved, and also of capping the power output to where the marketing department wants it. They do overcarb too, for similar reasons, when marketing demands they make a poor breathing old engine into a rorty snorty feeling sports engine, and damn the tractablity. Manufacturers used to bodge things almost as much as back street tuning companies do now. Lack of money for new designs and new production lines often held them back.
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Feb 21, 2008 16:41:22 GMT
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I guess the NA "more power" attitudes came into play over here, because we frequently got carbed cars with 'room to grow' on them. The Rochester Q-jet on some of the 70's GMs was easily altered for better flow while retaining low end. The Ford 302 FREQUENTLY suffers from overcarbing though, it's hates overly large carbs on stock cams, etc. Huge carbs with vacuum-driven secondaries to run extra barrels at wide open throttle, etc. The SU seems to compensate for part throttle torque loss by having that piston moving up and down, the loss would solely be a wide open, wouldn't it? I still fail to see how two 2" barrels is too big for a 4 cylinder engine. It isn't solely a carb-based issue I'd think. A poorly flowing cylinder head/manifold would also come into play here, or too-small valves, or 'classic' engine design. Admittedly, the flathead probably isn't the best flowing device, but lumping engines together by displacement is probably a bit of a generalization in regards to carb sizing.
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1982 VW Rabbit 4-door (apart) 1992 Passat Wagon Syncro (daily)
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Feb 21, 2008 17:32:41 GMT
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Well, the piston in an SU carb does help with part throttle and low rpm running, but you still get a loss from oversized carbs. The piston is hardly the worlds most aerodynamic shape!
Displacement doesn't come in to it, nor does the VE. All that really matters is the combustion efficiency, and power output. To make power, you have to get a certain amount of fuel/air mixture into the engine. The thermal losses, compression, valve overlap, optimisation of the timing, and suchlike come into play here, but bottom line is, you don't get the power unless you get the air through the carb.
The effects of the combustion efficiency on the power output is pretty small compared to the breathing factors. Higher dynamic compression and better timing only get a few percent more out of an engine, so it is very much secondary when it comes to figuring out carb sizing.
Engine tuning is about matching components with close to equal ability. Ultimately, that ford engine is restricted by its low compression. You can only get a sidevalves compression up so high, and the breathing isn't too great either. If all of the relevant components are specced up for the same power output, you get the best possible engine of that power output.
Short of forced induction, (which is another kettle of fish) that engine isn't going to reach the 300bhp+ twin HS8s can manage. So you can only loose out by fitting carbs so much bigger than necessary.
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Feb 21, 2008 18:55:29 GMT
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So, I think then we can both agree on the fact that the carbs he has to go on it may be too big for that particular engine, but not an engine of a different design then, that is far more efficient. It's a poor example, but take that 4 cyl side valve engine and compare it to (for example's sake), a modern 8v 4cyl. What's good for one, is probably not the best for the other. It's apples to oranges I know, but in a theoretical sense, a high flow modern head could easily use the two large carbs to it's advantage, whereas the classic head might not be able to. Another example is an aftermarket carb (S&S springs to mind) for a Harley Davidson cycle, they're 45mm-mouthed. Harleys never want for torque, that's for sure, and they run 1300cc setups on top of that. Again, apples to oranges though. I'm not trying to out-debate anyone here, as I'm just a shadetree carb tuner/engine builder, just offering up my (erred?) viewpoint.
Also, I think it's worth it to mention that 188 ft/lbs is an amazing amount, and if he were to use the larger carbs to gain more top end, he could probably afford to spare a few ft/lbs down low and still have a car with top notch driveability.
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1982 VW Rabbit 4-door (apart) 1992 Passat Wagon Syncro (daily)
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