10 replies to this topic

[min ritz ryan]

Hi all, I have a standard 1275 engine and was trying to find a way to get the best performance out of it, without changing the camshaft or enlarging the pistons. And was wondering would installing 1:5 roller rockers improve the performance/ enhance the engine power compared to standard rockers?

 

Also, would enlarging the exhaust and inlet ports on the manifold and cylinder head, be a good idea?

[minilee94]

Yeah one of the best things to do is the head polish and porting and bigger valves !

Also the rockers you won't see or feel a difference at all 151 you will get a few bhp increase up top but lose some down the low end

If your not willing to change the camshaft then there isn't really a lot you can do for power other than stage 1 kit etc but even then you won't notice it massively

[min ritz ryan]

Oh, okay. Thanks. I shall save my money at bingley then, aha

 

And just port it

[Carlos W]

Why don't you want to change the cam?

[min ritz ryan]

To be honest, I cant be bothered to strip my engine down and the fact im focusing on restoring my bodywork at the minute so got too much on my plate as is

[ace01]

1.5 rockers give more lift, but not duration.  I look at them as a way of almost taking the cam up to the next spec.  Therefore using them combined with a bit of headwork is likely to give an increase. Unless you need the look etc of roller rockers a good set of forged 1.5s like the MiniSpares ones are fine.

 

Personally, I would'nt enlarge the ports, I would just clean up the chamber, and if you're confident, shape the chamber.  Enlarging the ports will slow down the intake, which is not what you want. 

[ACDodd]

Hang on a minute. The measured duration the the valves is longer, as is the increase in overlap lift when using 1.5 rockers. People must ensure that when they give technically correct answers when helping people.

[min ritz ryan]

Blimey, very different sides here.

What would be best to do, buy 1:5 rollers or not?

And what if I just enlarge the exhaust ports?

[Turbo Phil]

If your engine is standard the best thing you can do to improve performance is to fit a stage one kit. This will give the biggest improvement in performance especially for the cost.
Simply enlarging the ports on the head will gain you basically nothing for performance, infact it could make it worse {as it reduces gas speed} This is because the primay restriction is not the port itself, but the guide boss, the throat & valve seat. Not until larger valves are install & higher lifts are used do the ports need enlarging to any real degree.
To work a head properly you'll need more than a Dremel, it will take you until the end of time using one of those ! Lol

Phil.

Edited by Turbo Phil, 25 January 2014 - 01:50 PM.

[Cooperman]

As Phil so rightly says the key to releasing more performance from the A-Series is to gas-flow the head. the critical (and poor as standard) areas are the throats and the combustion chambers.

The throats are restricted by the valve guide bosses and the poor shape & finish of the throat as it goes through 90 degrees up to the valves.

The combustion chambers are restricted by the fact that the edges of the valves are 'shrouded' by the edges of the chamber and cutting these back to allow the mixture to flow in better will make a lot of difference.

Once the chambers have been opened up the head will need to be skimmed to get the chamber volume correct for the ideal compression ratio.

Phil does some superb head work, so if you want to get your head flowed, he would do it, assuming he's not packed out with work.

Only when the head is improved is it worth considering cam changes.

One note of caution. If the condition of the engine is not excellent, by modifying it to give increased power you may hasten its demise.

[Carlos W]

WOW

 

AC Dodd, Cooperman and Turbo Phil commenting on the same thread! 

 

This is probably the best thread on the forum!