Who says stock Yank motors don't make power...

[Evoluzione]

R8VXF said:

Evoluzione said:

VVT doesn't alter the cam lift nor duration, it changes the timing of the cam to give more overlap at high rpm which is what you want for power. Large amounts of overlap at idle are not desirable.

Hmmm, so how does vvt on the LT series increase overlap? By magically regrinding the cam? I may be wrong but vvt generally works by opening the valves earlier in the stroke to give more time for the air to get in at higher rpm compared to the standard valve timing. What you are thinking of is probably VTEC YO. Two different sets of cams with different LSAs. Seeing as the dohc cams generally work from one chain, the LSA cannot be changed. At least, that is my understanding.

Then your understanding is wrong. Vtec alters everything, overlap, lift and duration as it uses a completely different lobe, VVT doesn't, it just changes the timing of the existing cam, it's used on one cam or both dependent on manufacturer.
I am talking about DOHC here, not SOHC, true if an SOHC engine is fitted with VVT then the overlap will remain the same, but both inlet and exhaust events will change together - that's another reason why they aren't very good, you have less variable and adjustability.

[kiseca]

R8VXF said:

Evoluzione said:

VVT doesn't alter the cam lift nor duration, it changes the timing of the cam to give more overlap at high rpm which is what you want for power. Large amounts of overlap at idle are not desirable.

Hmmm, so how does vvt on the LT series increase overlap? By magically regrinding the cam? I may be wrong but vvt generally works by opening the valves earlier in the stroke to give more time for the air to get in at higher rpm compared to the standard valve timing. What you are thinking of is probably VTEC YO. Two different sets of cams with different LSAs. Seeing as the dohc cams generally work from one chain, the LSA cannot be changed. At least, that is my understanding.

The system Alfa used on the Nord engine (i.e. the all aluminium DOHC unit that became the Twinspark in the 75) from about 1980 changed the timing on the inlet valves by rotating the inlet camshaft relative to the pulley. In this system the timing on the inlet cam is advanced at high revs while the exhaust timing remains unchanged. Both cams are driven by the same chain.

[DonkeyApple]

Evoluzione said:

Toltec said:

Sometimes it is how you get the air into the cylinder, at low rpm less valve area and duration mean higher peak air velocities and better distribution of fuel in the cylinder. This is what vvt is all about, gives you the high lift, long duration needed at higher rpm and the higher air velocities into the cylinder at low rpm.

VVT doesn't alter the cam lift nor duration, it changes the timing of the cam to give more overlap at high rpm which is what you want for power. Large amounts of overlap at idle are not desirable.

Yup, in simplest terms it allows for more aggressive cam profiles and timing to get the best out of the top end of the performance while retaining useability at lower revs. It helps make a racey engine more tractable when off the cam.

[R8VXF]

I stand corrected, though I think my point still stands that valve events need to happen earlier in the cycle to allow the required flow at higher RPM's.

I would be interested to see how they only change one cams timing though, purely from a knowing how things work point of view, not from an argumentative point of view

[CrutyRammers]

Evoluzione said:

With respect, until you post up some intimate figures it's hearsay.

I've had the argument before; two identical engines apart from the head. The 16v owners always bated the 8v guys, they always came back with 'Yeah, but i've got more torque or more torque at a lower RPM'. Until I posted up the figures and it wasn't the case, you can't argue with fact and physics. With two intake valves over one you are going to get more air into the cylinder at any RPM, full stop, you will get this from a gain in both CFM and velocity.

Indeed, the "2v has more torque" argument has been shown to be wrong any number of times. Off the top of my head, the golf GTI 8v vs 16v is one, the Alfa Romeo V6 12v/24v another. In both cases, the 4 valver produces more torque everywhere in the rev range. I've yet to see an example where it's the reverse. Apart from anecdotes from all the 2 valve owners of course.

It's like "vtec engines make no torque". People think that making extra torque at high rpm always means losing it at low rpm, but it doesn't necessarily work like that.

[Evoluzione]

R8VXF said:

I stand corrected, though I think my point still stands that valve events need to happen earlier in the cycle to allow the required flow at higher RPM's.

I would be interested to see how they only change one cams timing though, purely from a knowing how things work point of view, not from an argumentative point of view

Basically you just have to be able to turn the timing gear on the cam and lock it, there are a few different ways, Google it, it's no secret Fiats initial stab at it is reasonably easy to explain without diagrams.
They put the toothed wheel onto a helical spline on a hub on the cam, this meant as the wheel comes away from the cam it turns. They operated it by oil pressure: More RPM = higher oil pressure and so it pushed the wheel outwards, it twisted on its splines and changed the cam timing. It seems quite reliable as you don't hear of them going wrong much.

[Evoluzione]

CrustyRammers said:

Evoluzione said:

With respect, until you post up some intimate figures it's hearsay.

I've had the argument before; two identical engines apart from the head. The 16v owners always bated the 8v guys, they always came back with 'Yeah, but i've got more torque or more torque at a lower RPM'. Until I posted up the figures and it wasn't the case, you can't argue with fact and physics. With two intake valves over one you are going to get more air into the cylinder at any RPM, full stop, you will get this from a gain in both CFM and velocity.

Indeed, the "2v has more torque" argument has been shown to be wrong any number of times. Off the top of my head, the golf GTI 8v vs 16v is one, the Alfa Romeo V6 12v/24v another. In both cases, the 4 valver produces more torque everywhere in the rev range. I've yet to see an example where it's the reverse. Apart from anecdotes from all the 2 valve owners of course.

It's like "vtec engines make no torque". People think that making extra torque at high rpm always means losing it at low rpm, but it doesn't necessarily work like that.

A bit like 'turbolag'
Not with VTEC that's for sure, it's a system with no drawbacks. Vtec with turbo, well now were talking

What I can never understand is why (when manufacturers have spent millions developing them) do people take them off?
There are probably many reasons, simplification, maybe reliability. I think you can get an MX5 delete kit and the MR2 boys always bin the system from theirs, quite often it's on forum say so and to make money, but no-one has ever done any back to back dyno tests on some of them.

[R8VXF]

Evoluzione said:

R8VXF said:

I stand corrected, though I think my point still stands that valve events need to happen earlier in the cycle to allow the required flow at higher RPM's.

I would be interested to see how they only change one cams timing though, purely from a knowing how things work point of view, not from an argumentative point of view

Basically you just have to be able to turn the timing gear on the cam and lock it, there are a few different ways, Google it, it's no secret Fiats initial stab at it is reasonably easy to explain without diagrams.
They put the toothed wheel onto a helical spline on a hub on the cam, this meant as the wheel comes away from the cam it turns. They operated it by oil pressure: More RPM = higher oil pressure and so it pushed the wheel outwards, it twisted on its splines and changed the cam timing. It seems quite reliable as you don't hear of them going wrong much.

Ta buddy, similar to how the LT's use oil pressure to rotate the cam for VVT, just couldn't work out how you could only use it on one cam. VVT can actually be retrofitted to the LS series fairly easily but get a little overwhelmed at higher powers due to the higher oil pressure at the higher revs.

Really nice article on the LT1 explaining the design processes http://www.superchevy.com/how-to/engines-drivetrai...

[kiseca]

CrutyRammers said:

Evoluzione said:

With respect, until you post up some intimate figures it's hearsay.

I've had the argument before; two identical engines apart from the head. The 16v owners always bated the 8v guys, they always came back with 'Yeah, but i've got more torque or more torque at a lower RPM'. Until I posted up the figures and it wasn't the case, you can't argue with fact and physics. With two intake valves over one you are going to get more air into the cylinder at any RPM, full stop, you will get this from a gain in both CFM and velocity.

Indeed, the "2v has more torque" argument has been shown to be wrong any number of times. Off the top of my head, the golf GTI 8v vs 16v is one, the Alfa Romeo V6 12v/24v another. In both cases, the 4 valver produces more torque everywhere in the rev range. I've yet to see an example where it's the reverse. Apart from anecdotes from all the 2 valve owners of course.

It's like "vtec engines make no torque". People think that making extra torque at high rpm always means losing it at low rpm, but it doesn't necessarily work like that.

The problem is people aren't comparing the numbers produced by the two engines, they're comparing the feel. In the '80s 16V engines felt weak at the bottom end, because when you climb the rev range it eventually fills its lungs and gets much stronger. So the engine has a weak spot when compared to it's own strongest potential. 8V engines on the other hand were more consistent through their rev range, albeit with a lower limit. So they never felt weak... unless you were being left behind by the 16V alongside you I suppose.

This was one of the things that made the Opel/Vauxhall Red Top such a popular engine. It was strong throughout its range. It felt like an 8V but churned out the numbers of a 16V (75bhp per litre, which was pretty good back then!)

I do slso seem to recall from the '80s something about the large valve surface area of a 16V head had a limitation at low RPM, like low velocity airflow or something like that, which impacted performance. Maybe that was stories spread by those sticking to 8V heads, I don't know.

[R8VXF]

6.2l with 770bhp: http://www.superchevy.com/how-to/engines-drivetrai...

Granted not homologised for road, but pretty cool.

This article also explains LSA in a good way and demonstrates how changing it affects performance: http://www.superchevy.com/how-to/engines-drivetrai...

[Boosted LS1]

kiseca said:

I do slso seem to recall from the '80s something about the large valve surface area of a 16V head had a limitation at low RPM, like low velocity airflow or something like that, which impacted performance. Maybe that was stories spread by those sticking to 8V heads, I don't know.

This is what I read. Probably Vizard or Dave Walker writing for Fast Car or a similar tuning magazine of the period.

[Boosted LS1]

kiseca said:

I do slso seem to recall from the '80s something about the large valve surface area of a 16V head had a limitation at low RPM, like low velocity airflow or something like that, which impacted performance. Maybe that was stories spread by those sticking to 8V heads, I don't know.

This is what I read. Probably Vizard or Dave Walker writing for Fast Car or a similar tuning magazine of the period.

[Jedilai]

kiseca said:

I do slso seem to recall from the '80s something about the large valve surface area of a 16V head had a limitation at low RPM, like low velocity airflow or something like that, which impacted performance. Maybe that was stories spread by those sticking to 8V heads, I don't know.

True, for low rpm volumetric efficiency (how much air gets into cylinder before inlet valve closes) its hard to keep up the speed of the air/fuel entering if the area is larger as it is with 4vpc. Either it is a compromise or intake systems allow for it through variable inlet manifold geometry or variable valve lift etc. I can only deduct the disadvantages of 4vpc at low rpm are not as bad as the disadvantages of 2vpc elsewhere. There are always exceptions though.

[CrutyRammers]

kiseca said:

The problem is people aren't comparing the numbers produced by the two engines, they're comparing the feel. In the '80s 16V engines felt weak at the bottom end, because when you climb the rev range it eventually fills its lungs and gets much stronger. So the engine has a weak spot when compared to it's own strongest potential. 8V engines on the other hand were more consistent through their rev range, albeit with a lower limit. So they never felt weak... unless you were being left behind by the 16V alongside you I suppose.

Very much this, I think. Plus the bit of human nature that doesn't want someone else's toy to be better.

Boosted LS1 said:

kiseca said:

I do slso seem to recall from the '80s somet about the large valve surface area of a 16V head had a limitation at low RPM, like low velocity airflow or something like that, which impacted performance. Maybe that was stories spread by those sticking to 8V heads, I don't know.

This is what I read. Probably Vizard or Dave Walker writing for Fast Car or a similar tuning magazine of the period.

I remember the same, but IIRC that's referring to when you tune for maximum output, using all of the breathing capacity of the 4 valves at high rpm, with mad cams and tiny power bands. Not for any sort of road tune.

[RoverP6B]

Evoluzione said:

There are a few good reasons why the Meercans still use carbs, 2v per cyl and inches - one is because they're 20yrs behind everyone else.

They don't use carbs, haven't in donkey's years, except in NASCAR, and even there I think fuel injection is making inroads. As regards cubic inches, I find them (like most Imperial units) much more useful than the equivalent metric units.

[RoverP6B]

swerni said:

Again, substantially more HP than claimed - what have you done to it, if anything?

Regarding those saying the dyno test wasn't representative - you've got to have an alternator and battery to run the ECU, ignition, injection etc, and the lack of an exhaust only compensates for the lack of a proper induction system having air rammed into it by the car's motion...

[Ali_T]

832ark said:

That's pretty pathetic. Honda were producing 100bhp/litre NA cars in the 80s.

Honda's best current best is 78bhp/litre in the UK, and Mazda's is 75. Honda's 1.4 litre currently makes 17 bhp less than their' 1.4 in the '80s. They've come a long way....the wrong way!

[R8VXF]

RoverP6B said:

swerni said:

Again, substantially more HP than claimed - what have you done to it, if anything?

Regarding those saying the dyno test wasn't representative - you've got to have an alternator and battery to run the ECU, ignition, injection etc, and the lack of an exhaust only compensates for the lack of a proper induction system having air rammed into it by the car's motion...

That will be at the wheels if I know Surrey Rolling Road, factor in the 15-20% driveline losses on top of that figure...

[Coatesy351]

RoverP6B said:

Evoluzione said:

There are a few good reasons why the Meercans still use carbs, 2v per cyl and inches - one is because they're 20yrs behind everyone else.

They don't use carbs, haven't in donkey's years, except in NASCAR, and even there I think fuel injection is making inroads. As regards cubic inches, I find them (like most Imperial units) much more useful than the equivalent metric units.

NASCAR used carbs for so long because it was easier to police rule bending with them rather than efi. They all run a standard McLaren efi system now.

[R8VXF]

swerni said:

I wouldn't call 12- 13% substantial.

That would be your transmission losses if I am not wrong