1.4 Sliver & Black Tops & Cams

rossnunn · Post by **rossnunn** » 14 Jan 2005, 05:55

whats the differance? I can't remember for love nor money.
I was looking at cams too. Where do they take the power from? They can't just make more power apper can they??

Post by **RichardW** » 14 Jan 2005, 12:48

1st Q: Eh? Can you ask again in English??
2nd Q: Eh? I think you are asking how a different cam can make the engine produce more pwoer? It's all down to the duration, timing and lift of valve opening. by changing these (a function of the shape of the cam shaft) you can get more power out of the engine - usually at higher revs, at the expense of low speed tractability (ie it won't idle any more).

rossd · Post by **rossd** » 14 Jan 2005, 21:16

The black top TU engines have finger rockers above the camshaft, whereas the Silver top TU's have roller type rockers.

rossnunn · Post by **rossnunn** » 15 Jan 2005, 01:53

does the silver top produce more bhp because of this? I ask as a 106 1.4 XSI produces 100 bhp where as a standard black top 1.4 is around 75 bhp

Sl4yer · Post by **Sl4yer** » 15 Jan 2005, 02:30

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by rossnunn

a standard black top 1.4 is around 754 bhp
<hr height="1" noshade id="quote"></blockquote id="quote">
I'll have one of those then! [:D] (Sorry, somebody else would have done it!)
I guess the question is one that I used to wonder about - how did the AX GT (85BHP) and GTi (100BHP) engines differ from the standard 1.4 engine (75BHP)? I'm sure the cams are something to do with it, possibly a higher rev limit as well? (Apart from the a multipoint injection system on the GTi I'm sure!)

jeremy · Post by **jeremy** » 15 Jan 2005, 16:51

Engine tuning is a fascinating subject which after 100 or more years of development still hasn't reached the ultimate conclusion. Basically the object is to produce an engine that is suitable for its intended purpose which means that there are different considerations for a road car and a track car. You have only to look at the Formula 1 pitstops to see what i mean - those engines may well produce about 300 bhp at 18,000 revs but they won't idle properly and are ridiculously easy to stall unintentionally!
The name of the game is to get as much mixture (not air, not petrol, but a gas mixture of both) into the cylinder and fire it at the right time. the amount of mixture can be affected by carburrettor size, manifold design, combustion chamber shape, valve size, valve lift, valve timing and exhaust design - so just to start with we have a few issues to consider and juggle!
manufacturers design engines as an entity to do a job. I think you will find that the AX GT has a more complicated carburrettor than the base model, and in fact its carburrettor looks like 2 which is what it essentially is. if you look dewn the top you will find it has 2 air holes (chokes) one of which is larger than the other. most of the time the engine runs on the small one which makes it tractable round town and pull well from low revs. When the throttle is opened past 2/3rds travel the second one opens admitting loads more mixture and the engine produces more power. With this arrangement the engine can use more extreme valve timing - (hence the difference in cam specification) to admit more mixture and probably different ignition timing and also a free flowing exhaust.
So what I'm saying is that all the bits go together. Change one and the engine won't function as well as you expect. Put the camshaft from the higher-power engine on the base one and you probably won't get the high revs power you expoect as the carb and exhaust can't handle the increased gas flow necessary, and at low revs you don't have the smaller choke to take care of things at low revs.
i don't think its quite as simple as it looks!
jeremy

rossnunn · Post by **rossnunn** » 15 Jan 2005, 20:13

ok so is the only differance between a black top & silver top 1.4 the rockers?
I've read the 106 XSI 1.4 produces 100 bhp. How easy is it to identify one & what else was it used in?

citroen_ash · Post by **citroen_ash** » 16 Jan 2005, 00:56

Ax Gt has massive valves compared to standard engine aswell as twin choke carb bigger exhaust
<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Sl4yer

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by rossnunn

a standard black top 1.4 is around 754 bhp
<hr height="1" noshade id="quote"></blockquote id="quote">
I'll have one of those then! [:D] (Sorry, somebody else would have done it!)
I guess the question is one that I used to wonder about - how did the AX GT (85BHP) and GTi (100BHP) engines differ from the standard 1.4 engine (75BHP)? I'm sure the cams are something to do with it, possibly a higher rev limit as well? (Apart from the a multipoint injection system on the GTi I'm sure!)
<hr height="1" noshade id="quote"></blockquote id="quote">

citroen_ash · Post by **citroen_ash** » 16 Jan 2005, 00:58

106 xsi and ax gt engines have a cast iron block not ally
<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by rossnunn

ok so is the only differance between a black top & silver top 1.4 the rockers?
I've read the 106 XSI 1.4 produces 100 bhp. How easy is it to identify one & what else was it used in?
<hr height="1" noshade id="quote"></blockquote id="quote">

Post by **cheesesliceking** » 16 Jan 2005, 03:35

Sorry the AX GT has an Alloy block... for sure.[8D]
<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by citroen_ash

106 xsi and ax gt engines have a cast iron block not ally
<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by rossnunn

ok so is the only differance between a black top & silver top 1.4 the rockers?
I've read the 106 XSI 1.4 produces 100 bhp. How easy is it to identify one & what else was it used in?
<hr height="1" noshade id="quote"></blockquote id="quote">
<hr height="1" noshade id="quote"></blockquote id="quote">

VisaGTi16v · Post by **VisaGTi16v** » 16 Jan 2005, 04:58

Thats what I thought. The GTi had the iron lump with multipoint injection. There wasnt really much speed difference due to the added weight. To really confuse things they made the Ax GT with single point injection for a while as well. No idea if that model was sold in this country and it was still badged as GT not GTi. Weird french!

rossd · Post by **rossd** » 16 Jan 2005, 23:14

The only differnce between the AX GT engine (TU3S) and the normal 70/75bhp version (TU3A/F/M wotever) is the cam and the carb. The camshaft is a lot 'wilder', eg it has a bigger overlap, allowing better cylinder filling and more efficient combustion. The timing advance is also slightly different. The valves are the same size in the 85bhp and 70bhp versions. The 100bhp version had multipoint injection larger valves etc, not too hot on this engine, but I did do a lot of research on the TU3 and TU3S engines a few years ago.

rossnunn · Post by **rossnunn** » 18 Jan 2005, 22:56

ok so is the only differance between a black top & silver top 1.4 the rockers?

rossd · Post by **rossd** » 19 Jan 2005, 02:19

Im not sure thats the *only* difference, but its certainly one of them.

rossnunn · Post by **rossnunn** » 19 Jan 2005, 18:35

is it the MPI 1.4 that has the 100bhp & the SPI thatr has 70odd bhp?