Converting a slant 4 to run 14 to 1 compression

[yachtsman]

To do this I need to machine the block.  I'll be running E 95 ethanol so pre-ignition (pinking) won't be a problem.  Does anyone know how far the pistons go down in a standard block. ;)

[andy thompson]

Most Triumph engines seem to run  the pistons about 0.025" down the block out of the factory +/- a few thou"
If you massively over skim the block and head of a TR7 engine will the slanted bolts studs still fit? Also expect to need bigger cutouts in the pistons.

TR7 heads are very tricky to skim excessively because the inlet valve is bigger than a Stag and overskimming will hit the valve seat.

Maybe you need to get a 1850 head with smaller inlets or convert a more durable engine????

[Gt6s]

As Andy says. The valves and seats will limit how much you can skim off the head, not enough to raise the compression to what you want.

[andy thompson]

I think if you try to convert a TR7 engine to run 14:1 you are as mad as cheese - why not increase compression by supercharging??

[yachtsman]

The block not the head!!!   Perhaps I am as mad as a cheese, but I was going to look in to boosting  the engine next year if I think the bottom end will take it

[Beans]

I think the bottom end is the weakest link here.
Just started on a new Sprint engine for ‘t Kreng,
and bracing the bottom end is high on the to do list.

Also taking that amount of the block will give problems with the angled studs,
the holes being angled will move to the outside.

[Beans]

lagerzok wrote:

... Maybe you need to get a 1850 head with smaller inlets ...

In that case you'll need an early ( don't know how early though) head.
Most 1850 heads I have seen had the same valve diameter as a TR7.

[andy thompson]

Not actually sure if the 1850 head has smaller valves then - I know the Stag does - kind of "assumed" the 1850 would too

How does machining the block roduce more compression? Where will the protruding pistons go?

[yachtsman]

Still thinking about shoehorning that Rover SD1 2600 into the TR7 .  That bottom end is supposedly overcoming all the faults of the  TR250 then if I can make it fit, get a SS exhaust manifold Inlet manifold and that's it.   Getting a SD1 is the old up.

[yachtsman]

Still thinking about shoehorning that Rover SD1 2600 into the TR7 .  That bottom end is supposedly overcoming all the faults of the  TR250 then if I can make it fit, get a SS exhaust manifold Inlet manifold and that's it.   Getting a SD1 2600 auto or SE is the hold up.

[Beans]

lagerzok wrote:

Not actually sure if the 1850 head has smaller valves then - I know the Stag does - kind of "assumed" the 1850 would too ...

Earlier Dolomite 1850's indeed did had smaller valve heads, but they changed that to the larger valve heads as used on the TR7.
Probably at the time they launched the TR7, but that's just a guess on my part.

[yachtsman]

Having taken the comments into account I will look into all the methods of increasing the compression, other than by skimming the head and planning the block, especially as I need to raise  the compression so high.

[andy thompson]

Custom pistons with a pop up?

[Chriss]

I would not trust a slant 4 to 14:1 even if you dont rev it.  I had a racer built by Mark Field of Jigsaw.  He had some success with it and on 48DCOEs and 12.5:1 he claimed 230 BHP with 750 Kg.  It certainly went, but not very far.  The head gasket could not cope.

[yachtsman]

So 12 to 1 would be easy then.  The only slant 4 I've had was in a SAAB

[Chriss]

2271 wrote:

So 12 to 1 would be easy then.  The only slant 4 I've had was in a SAAB

The Saab slant 4 is a good dependable engine.  I have driven over 1,000,000 miles in 5 different cars behind them in without serious problem, but I would not trust one of them on 14:1 CR either.