9 replies to this topic

[DEXISWOLF]

how much difference would it make to a 998 with twin 1.25 carbs, lcb manifold and straight through exhaust and standard cam or would i need to change cam aswell to to make it worth while just wanting ideas for margarets engine

[callyspoy]

I think you'd still notice a fair gain, but yes, it would be optimised with a 266/MG Metro cam.
The benefit of a standard lift cam though is the possibility of not having to pocket the block...if you were going to pocket the block anyway, and the engine is out of the car, personally it'd be a no brainer to fit a better cam, well to me anyway

[Spitz]

So with a standard 998 cam, and a 1275 head that hasn't been "shaved", pocketing the small bore block isn't required?

[DEXISWOLF]

thanks for fast reply i did want to still keep standard cam to keep costs down but would but would the 1275 head still need anything doing with it to make it fit its just that ive been searching forums and theres always two different answers to that queastion or is it a matter of trial and error

sorry if im sounding daft its just that ive read that you dont need to change cam to get a good power increase

Edited by DEXISWOLF, 16 March 2012 - 03:05 PM.

[Cooperman]

No, it's not trial & error, it's engineering measurement, as usual.
Measure the total lift of the valves using a DTI. That's valves, not push rod tops.
Then measure the dimension between the face of the head and the valve face. This dimension must be less than the maximum valve lift.
If the head is off, measure the lift at the top of a push rod and multiply by 1.3 for valve lift.
If the dimension from valve face to head face is less than the valve lift by 0.040" or less you can have the head machined to recess the seats by 0.040" then you'll have clearance. If not, then the block must be pocketed.
Ignore the thickness of the head gasket as this is best considered as the tolerance figure.

[twrminisport]

If you want to go trial and error then by all means be my guest...

MEASURE EVERYTHING.
Then when you have done this. MEASURE AGAIN

Do the above process 10 times until you are bloody well sure it won't touch.
And ignore the gasket thickness.

If it will touch, then you may be able to recess the exhaust valve to alleviate any issues.
Generally however you should pocket the block.
Most machine shops will do this for you

If you go trial and error with any engine. Expect a trial and error engine. Ie. FU**ED

Jesus

[Cooperman]

If you want to go trial and error then by all means be my guest...

MEASURE EVERYTHING.
Then when you have done this. MEASURE AGAIN

Do the above process 10 times until you are bloody well sure it won't touch.
And ignore the gasket thickness.

If it will touch, then you may be able to recess the exhaust valve to alleviate any issues.
Generally however you should pocket the block.
Most machine shops will do this for you

If you go trial and error with any engine. Expect a trial and error engine. Ie. FU**ED

Jesus

Yes, absolutely right. How anyone can think they can build an engine without measuring, machining and measuring again is amazing.
I was asked how cheaply I could build an engine. The simple answer is that it can't be done.
You strip the engine, detail inspect and measure. Get it machined and do a trial build then measure again. The after final machining a final trial build is usually needed before final and very careful asembly.

[DEXISWOLF]

thanks for answers but i was saying trial and error to see if there was noticable power increase or not wouldnt like to do something like that if i wasnt shore if it would kill engine or not plus i wouldnt hurt margaret

[Algordo1100]

I have a 998A+ with a 1275 head. Its running a minispares freeflow manifold through an RC40, minispares alloy inlet. HS4 carb. cam and rockers are standard 998. The block is not pocketed. The engine has a 1275 type water pump with no bypass outlet, and a smaller pulley is fitted that clears the head. The 1275 parts are all from an A+ metro.

This engine is a different machine to a standard 998. It is considerably more powerful right through the range.

Not pocketing the block is probably a stupid idea. I have only got away with this through the skin of my teeth with a standard cam. I don't recommend anyone tries it. This engine is soon to be overhauled and a different cam will be fitted to unleash more of the head's potential.
Whilst this is being done I will be pocketing the block.

As I said though, even on the standard cam it is a nice setup. Great usable power with a smooth delivery and good economy. I would recommend a block pocketing though :)

Al

Edited by Algordo1100, 16 March 2012 - 06:07 PM.

[DEXISWOLF]

I have a 998A+ with a 1275 head. Its running a minispares freeflow manifold through an RC40, minispares alloy inlet. HS4 carb. cam and rockers are standard 998. The block is not pocketed. The engine has a 1275 type water pump with no bypass outlet, and a smaller pulley is fitted that clears the head. The 1275 parts are all from an A+ metro.

This engine is a different machine to a standard 998. It is considerably more powerful right through the range.

Not pocketing the block is probably a stupid idea. I have only got away with this through the skin of my teeth with a standard cam. I don't recommend anyone tries it. This engine is soon to be overhauled and a different cam will be fitted to unleash more of the head's potential.
Whilst this is being done I will be pocketing the block.

As I said though, even on the standard cam it is a nice setup. Great usable power with a smooth delivery and good economy. I would recommend a block pocketing though :)

Al

. Thanks that helped alot just wanted to know so I can try and increase power without changing cam then if I want can get it pocketed in future and change cam because Ive been told by my dad and other people that it does work with standard cam so I just wanted a deffianet answer but I think il get It pocketed then if I do go with it thanks for help