Rattle from engine

[JC.]

Hmm so I was on the right lines then?
My P6 engine apiers to have tin gaskets on atm and is the 9.35:1 CR model
Engine number on the block is readable.

What steps should I take to avoid making the same booboo?

[mgbv8]

Before you put the heads on JC, make sure the pistons done come above the bore. And use composite gaskets. Those pics are really strange.

[adamnreeves]

This what I would do. Measure the CC of the original heads. Measure the CC of the new heads. I have just worked out that :

new CR = ( old CC * orginal CR ) / new CC

not sure what the CR limit is for the rover heads and normal fuel but I would be nervous going above 10.4. Someone else needs to answer this.

As mgbv8 says use composite gaskets as these are thicker and essentially increase the CC of the combustion chamber and reduce the compression ratio by 0.6:1

Just looked at the rimmer bros site and can see that heads for you engine might have a 34cc combustion chambers. If you went for latest heads which are 28cc then :

new CR = ( 34 * 9.35 ) / 28 = 11.35:1
use composite gaskets to reduce form 11.35:1 to 10.75:1

[JC.]

Assuming the CC of the new heads is larger than the CC of the original heads is it still possible to use tin gaskets?
I thought that dropping the CR equates to a loss in power/torque despite the better chamber shape of the SD1 heads?

This engine is certainly not going to be particularly highly tuned at all. 150bhp at the flywheel would do me nicely which is what I was hoping to achieve by fitting the Sd1 heads.

Its only a temporary engine tbh. The longest its going to be in the car is 2 years. Doubt i'll do any more than 15k miles with it.

[adamnreeves]

Not sure of the CC variances between heads but if the new CC is larger then the CR will reduce. I do not think this means no need to use composites as this depends on the combusion chamber shape as well as the CC of the cylinder at TDC I guess, if indeed the cylinder stays below the deck, which I would hope it does.

You might find this useful:

http://www.rimmerbros.co.uk/rimmer/rover/v8engine/heads

Assuming the CC of the new heads is larger than the CC of the original heads is it still possible to use tin gaskets?
I thought that dropping the CR equates to a loss in power/torque despite the better chamber shape of the SD1 heads?

This engine is certainly not going to be particularly highly tuned at all. 150bhp at the flywheel would do me nicely which is what I was hoping to achieve by fitting the Sd1 heads.

Its only a temporary engine tbh. The longest its going to be in the car is 2 years. Doubt i'll do any more than 15k miles with it.

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[katanaman]

SD1 heads and P6 heads have the same 36cc combustion chamber volume, chamber shape is the same too its only the valve size that is different. The only way fitting SD1 heads on a P6 engine with tin gaskets would cause a problem is if they have a heavy skim on them otherwise everything is exactly the same barring the better flow. Depending on what your doing with the engine you could use comp gaskets and take the hit on lower compression. It will still have higher compression than most 3.5 engines. Originally the P6 has 10.5:1 with comp gaskets you would be nearer 9.7:1. Basically it would be about the same as the vitesse engine.
For the pistons to physically hit the heads on a running engine the block would need to be decked by around 30 thou. This leaves the original stamped engine numbers very faint, 40 thou removes them completely. So from that you can tell if your engine is decked or not and roughly by how much. If the numbers have been re-stamped then its most likely had a heavy skim but also likely the pistons have been skimed as well, assuming the engine ran.

[JC.]

Thanks for that guys.
I was advised that the SD1 heads make more power on my P6 engine.
Basically, I am trying to convert my '79 MGB GT to V8 power on a student budget. I am using the engine out of a P6 that has since been scrapped due to terminal rot.
The intention is to get the engine into the B as-is and use it for a year whilst I build up a 3.9 engine with a wild cam and all the other nice and expensive stuff I see people on this site buying and playing with.

The numbers stamped into the block are 9.25:1CR followed by 48114596D
Does this have any bearing on whether or not I will have any problems?
Id quite like to avoid the pictures that came from the V8 moggy

[minorv8]

The only accurate option is to detemine what you currently have, i.e. which piston dish size, what is the distance from piston crown to block deck at TDC, chamber size and gasket volume. The quoted values for chamber may differ a lot. Even the factory CR values may not be what quoted.

Plastic orange, have you measured the piston crown to deck distance at TDC ? Currently e.g. pro engine builders in USA try to achieve a figure of 0.035-0.04" WITH gasket to produce an optimum squish volume. Less than that and there is a serious risk of detonation. OK, the optimum value varies from engine to engine but I would guess that this is what caused your problems.

As for CR, static ratio and dynamic ratio are 2 different things. Cam timing affects the dynamic ratio so in the end it is a question of how well the parts match each other. But, you need to KNOW the static CR, to only guess based on what parts are thrown together.

[kiwicar]

minorv8
I fully agree with the 35 to 40 thou figure but I understood it was to allow for rod elongation when the engine gets hot and rod stretch when the thing is reved hard, (all the stuff I have read says ally rods should use 50 to 65 thou for this reason). The other reason is to allow for variations in piston height in the bore so the home engine builder does not have to check each one.
There was a good article a while ago in one of the US magazines I get on a guy running a 302 ford with flattop pistons and 20 thou of clearance but to do this he had matched all 8 rods (he worked for a performance parts shop and had a few to select from), machined the crank spot on and then finnished the deck heights on the flat tops himself, (yes I know standard practice for many over here) he claimed about 15bhp for this at a given CR and was meant to make it more resistant to detonation as there more swirl in the combustion chamber.
Mike

[plastic orange]

I'll measure things up, plus will post some more pics showing the differences in combustion chamber between the heads I have. Thanks for everyones suggestions so far.

Pete

[minorv8]

Here are a couple of good articles:

http://www.popularhotrodding.com/tech/0 ... ion_ratio/

http://www.chevyhiperformance.com/techa ... nce_guide/

Yes, reducing the quench or squish whichever term one wants to use becomes critical if there are loose tolerances, too loose and piston might hit the head. Also, if the mixture is too lean the small quench may lead to unwanted burn characteristics. Usually faster burn rates require less ignition advance (again more or less dependant on the chamber design) Read the articles and you will see how important it is to know what you are assembling. BTW, the first articles is written by the same David Vizard who did a lot of work with A-series and Ford engines, he´s now building fullsize engines...

[kiwicar]

I am pretty sure Mr vizards first published book was on the porting of small block chevy heads. before he started on minis But the mini work is why so many of the heads he designed for the SBC have chembers the same shape as the 12g940 castings (oh and thst it is a good chamber shape )
Mike

[minorv8]

Correct, and it only took something like 40 odd years since the birth of SB Chevy

[john 215]

Hi Pete,sorry to see your horror pics,another cause of such damage i have seen has been either running way to lean or incorrect ignition timing normaly dynamic advance.However both will cause high temp gauge readings,just a thought.
Good luck,John.

[ihatesissycars]

Is there any signs of debris from sonething falling into the engine?

That looks too much to be just detonation to me.