Engine and Transmission Tech

Head combustion chamber size:

Early Rover 36-37cc

Late Rover (10 bolt) 28-29cc

300 Buick (alum.) 53-54cc

These are the most common reported CC sizes.

I have all three in my garage. Some cold, rainy day I need to cc them.

TA should be 1 to 4 CC larger than late Rover heads according to that and my measurements of the TA chambers

Jim

Remember those pistons are for a V6 so you have to buy 2 more.

I do like the pistons Jim N. suggested, but I am concerned about the overbore requirement. So, I want to look a bit more before I decide. Can anyone tell me the optimal dimension (at or below the deck) for the combination of the rod length and compression height for both the 300 and Rover/TA heads? I've tried to verify the dimensions but haven't seen exact numbers and I'm not convinced my backing into it calculations are correct. I saw Jim B. say earlier that with a 6.2" rod and a 1.405" CH, the dimension is at top of deck--what confuses me is that I have in my notes that the standard rods of 5.963" + Buick 300-4 pistons at 1.859" CH = 7.822". I'm not sure where I got that from, but perhaps the Buick V8 site (?). And I think I understand that, at least for the Rover/TA, we'd want to be at top of deck (whatever that number is) and have a dished piston with about 3-7cc of volume in the dish?

I also prefer, as Jim B. mentioned, to use composite gaskets, so I know that will make a difference. This decision seems to be driving a lot in my engine and I don't trust that I have it right yet--so I appreciate your patience with my (lack of) knowledge. Thanks much. --Eric



Edited 1 time(s). Last edit at 11/18/2022 04:43PM by Airwreckc.

Take your deck height: 9.543"
Subtract half of the stroke: 3.850/2= 1.925
Subtract rod length: 6.320

The result is piston height for zero deck. .040" thick gasket gives .040 squish.

Jim

For my (crank at the machine shop for 6 months) engine build, I first built a spreadsheet.

Using the numbers put up so far (I've made them metric), the Ebay pistons look close, except for the big squish. But decking the block to reduce it, and/or using a thinner gasket will push your compression higher than I think you want?

Jim,

Thanks, as always.

Chad, that spreadsheet looks great--any chance you could send it to me? And I assume these numbers assume using the 300's heads? If so, just curious if you did a version with Rover 4.6 heads? I'm comparing both options.

Thanks much to both of you.

Just to stir the muddy water, I do not think that the stock 300 heads are much, if any, better than the late Rover heads. Both well ported, the 300 wins easily.

Remember the chamber of the late Rover head is around 29cc and the 300 is around 54cc.



Edited 1 time(s). Last edit at 11/18/2022 06:59PM by mgb260.

Chad's spread sheet uses 300 heads. if you use the small chamber Rover heads you need around 35cc dish in the pistons.

At 29 cc for the head volume, you end up with ~15.8 compression.

-edit
Ha, Jim out typed me. And I wonder if squish matters much with (heavily) dished pistons and no squish-pad to speak of with the Buick heads?



Edited 1 time(s). Last edit at 11/19/2022 01:10PM by Roverbeam.

Ha, I was thinking I was close to figuring it out. There is a lot of great information here to evaluate.

Carl, I already have some 300 heads. I was originally leaning in that direction. One thing that made me think the Rover heads might be better is availability, in case of damage. What are your thoughts about durability of the 300 heads, especially at high compression?

Chad, subtract 35cc for the dish on the piston.

9.9 with 29cc Rover heads and -35 dished pistons.
But that's assuming the same compression height (or custom?) as the Ebay pistons.
I've spent the time in the past searching the various piston seller's sites, trying to find the magic combo of diameter, compression height, pin size, dish, cost, and quality. I know it's no picnic!

If you deck the block about .030 should put you around 10.3 or so. If you sonic check and bore .060 shouldn't be an issue, They sell .060 over pistons for the 300. I know a few have went .050 over.



Edited 1 time(s). Last edit at 11/18/2022 08:05PM by mgb260.

" What are your thoughts about durability of the 300 heads, especially at high compression?"

How much compression?

Mike Moor's 1964 Buick 300 is a factory 4bbl 11:1 engine. He has refreshed it a time or two, but the heads are original. He swapped out his 215 for the 300 in 1997 or 1998.



Edited 1 time(s). Last edit at 11/18/2022 09:06PM by MGBV8.

I don't think that ad had the dish volume, just the depth which is basically useless. If so, you can't assume a 35cc dish. Did I miss something?

Rover heads are a couple pounds heavier than Buick ones, are made from a little stronger alloy and are a bit denser so they will hold up a little better in a demanding application. In particular the bolt bosses are a little soft in the Buick heads. They can work fine but can also have issues, so be certain to use thick hardened washers under the head bolts and don't over torque the rocker shafts and accessories.

You can buy 4.6 Rover heads for about $200 each on ebay these days. The last set of 300 heads sold on ebay went for $400 + $85 shipping so that's a wash. No need to be tied to the 300 heads. If you end up with the single plane intake you'll be kicking yourself later on for using the Buick heads because you won't be able to swap to the TA heads to take advantage of the intake. This upgrade path can also include a roller cam, which doesn't necessarily have to be particularly radical to let you use modern oils in the engine. With that combo something in the 400 neighborhood should be pretty easy. The MGB can handle that. Just as importantly though the torque output will make driving it a very pleasant experience.

The 300 heads may flow noticeably more than the 4.6 heads or the difference may not be enough to feel, I really don't know. But the TA heads right out of the box are a big step up. Worth the money? I guess that depends on whether you have it to spend. I bought the bare heads and built them myself with used titanium valves and beehive springs for a good bit less than the complete heads cost. Took some machine work to do it but that only cost me time and I gotta say, cutting down titanium intake valves to fit was a very fun experience.

Jim

Jim, Just speculating on the dish cc's, could be 30 or 25. Have to measure.

Always best to measure. Maybe we can persuade Carl to do that. From what I've seen online though it should be 29cc.

Jim

I have seen the late Rover (10 bolt) head combustion chambers listed at both volumes.



I think you may find that it is actually a bit higher than 0.6:1. The compression ratio is calculated by dividing the swept volume and the static volume into the static volume. Therefore if you change the static volume (the bowl in the head and the piston) by 10%, the compression ratio will change by 10%. Rover reduced the capacity of the head from 36CC to 28CC to compensate for the composite gasket. Therefore a rough calculation would suggest that the composite gasket has a volume of around 8CC. The piston bowl on a 4.6 is around 22CC in a 9.35:1 motor. 4.6 bowls are some of the largest you will find in a rover V8. So with the old heads you would have a total static volume of around 58CC (36 ford head and 22 for piston). So if you increase the volume by 8CC by using a composite gasket you will increase the static volume by 8/58 or 14%. 14% of 9.35 is 1.3 change in compression ratio.

For a 4.0 motor the piston bowl is only 13CC, which would make a total volume of 49CC and the change would be 16% or a change in compression ratio of 1.5

I am not attempting to state that the above figures are 100% accurate in their calculation, but I think you will find that the change in ratio is above 1 or the equivalent of going from a High Compression Rover V8 to the standard Low Compression version.

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Tempest and Thor. With the introduction of the new Range Rover in 1994 a new head was brought into being, with a revised casting (No 2479) the head had larger ports than the Vitesse heads but retained the same valves and guides which were present from ~1993 onwards. The combustion chamber volume (29cc) was also reduced (by simply machining off more material on the face) to compensate for the increased thickness of the composite head gaskets and probably most noticeable, the 14 head bolts were reduced to 10, the 4 outermost being removed. Incase you're told otherwise, 4.0 and 4.6 litre heads are identical.
Casting Numbers: HRC 2479



Edited 1 time(s). Last edit at 11/21/2022 08:58AM by MGBV8.