11 replies to this topic

[neilbut1988]

Can anyone tell me what my engine will be like for driveability and a rough guide of what power it will make? Its a 1320 with a keith calver RE13ot cam, stage 2 mini sport head, 23D cooper s dizzy and a fully modified hs4 carb( i followed the yellow book by david vizard on this) it has a standard gearbox with a 3.1 diff fitted. Thanks

[Gremlin]

You'd be better off getting a HIF44 or 2 HS4's

[neilbut1988]

Ok but why? Would it run better?

[Gremlin]

The HS4 is not really big enough for 1275+, someone will be along soon with the flow rates. 1275+ engines generally draw enough air throughout the rev range to justify having a HIF44 or twin HS4's, it means that more of the needle will be used whereas if you used your single HS4 it would probably use more of the top end of the needle and at full throttle would probably be more restrictive than is necessary

[neilbut1988]

Would the car run better on a weber dcoe 40?

[Gremlin]

I don't know enough about webers to answer accurately sorry

[Cooperman]

A Weber 40DCOE has twin choke tubes of 40 mm each, whereas twin HS4's have, effectively, two choke tubes of 38 mm, so both have a better ability to flow mixture than a single HS4 (1.5" choke tube). 

 

I'm wondering how you get a 1320 cc engine. At +0.040" it is 1310 cc and at +0.060" it is 1330 cc. There are, so far as I'm aware, no +0.050" pistons which would give c.1320 cc.

 

It is impossible to give any idea of performance as with a single HS4 it will not breath well at the high revs needed to extract best performance from the cam's spec. However, that cam is not well described and no cam graph is available. It says 'similar to 286', but then says power is up to 6000, whereas peak power from a 286 is at 6400 rpm with strong power up to around 6800 rpm.

 

With a 286 twin HS4's, or maybe a single HS6/HIF44 is a minimum for carburation.

[neilbut1988]

sorry about the engine size, iv just look back in my photos and the piston are +30 item, i have no idea how old they are but they are mahle pistons and the engine seems to run ok on them, so would the weber be alot better the?

[carbon]

In my limited experience the low-mid speed torque with Vizarded HS4 on a good alloy inlet manifold is as good or better than twin HS2's. This is based on a 1293 and a 1330 with almost identical gearing and build specs apart from the carbs.

 

As far as maximum power with a 'vizarded' single HS4, on a well modified 1293/1310/1330 you should be looking at 80+bhp. You may get another 5bhp from a well set up Weber.

 

For a comparison between some of the carb options there is a good graph in Vizard's 'blue bible' (Fig 7.2 on page 76)

[Cooperman]

For a 1330 or any big engine, i.e. 1275 or bigger, using any sort of hot cam and big valve head it really is necessary to use twin HS4's or a 40 DCOE Weber. Even twin HS2's struggle with a modified 1275 engine. It is generally accepted that if using a single SU on a big engine it needs to be an HIF44 or an HS6 with a really good inlet manifold to get good top end power.

[KernowCooper]

And remember that a 40 DCOE weber unless modified the biggest standard choke is 36mm, and that with  the design of the head and only 1 cylinder is on the intake stroke at any one time, so you dont draw in air from both chokes.

[neilbut1988]

The weber that I have has 34mm chokes fitted so would I be better replacing them with 36mm chokes?