Rover V8 engine build for TVR Chimaera
Discussion
A question for cylinder head experts
I'm planning a new engine build for my Chimaera based on a rod/stroke/piston combination that will give me a static compression ratio in excess of 13:1 using composite gaskets and early 36cc heads. The pistons are forged flat tops. I know I can bleed the compression off with a wild cam, but even so, I still think this is too high and would rather it was around 12:1 for the cam I want to use.
What is the absolute maximum that the combustion chambers can taken out to without radically altering the shape or removing the squish band.
I'm planning a new engine build for my Chimaera based on a rod/stroke/piston combination that will give me a static compression ratio in excess of 13:1 using composite gaskets and early 36cc heads. The pistons are forged flat tops. I know I can bleed the compression off with a wild cam, but even so, I still think this is too high and would rather it was around 12:1 for the cam I want to use.
What is the absolute maximum that the combustion chambers can taken out to without radically altering the shape or removing the squish band.
PhysDoc said:
Thanks for your reply.
The pistons are Manley forged pistons, and the deck thickness is 0.185"
How deep dare I machine the bowl if I were to do that? What would be a reasonable minimum deck thickness?
Are you confusing deck thickness with crown thickness? I wouldn't machine those piston crowns. You certainly can't bowl them and even a dish won'y yield much more in the way of cc'c. The pistons are Manley forged pistons, and the deck thickness is 0.185"
How deep dare I machine the bowl if I were to do that? What would be a reasonable minimum deck thickness?
What is your piston to head measurement and head gasket thickness? Also, you say early heads? Please don't say they're pre-sd1.
Hi,
No, certainly not pre SD1 heads.
It's a 4.6 crank, 4.0L rods and the compression height of the pistons is 1.220". These are they http://www.modmaxracing.com/product-p/man594099mg-... I may well be confusing deck thickness with crown thickness: what is the difference?
By my reckoning that will leave the piston 0.4mm down the bore at tdc, based on stroke of 82mm, rod length 155.2mm and deck height of 8.96") I'll use composite gaskets with compressed thickness of 1.2mm.
No, certainly not pre SD1 heads.
It's a 4.6 crank, 4.0L rods and the compression height of the pistons is 1.220". These are they http://www.modmaxracing.com/product-p/man594099mg-... I may well be confusing deck thickness with crown thickness: what is the difference?
By my reckoning that will leave the piston 0.4mm down the bore at tdc, based on stroke of 82mm, rod length 155.2mm and deck height of 8.96") I'll use composite gaskets with compressed thickness of 1.2mm.
Edited by PhysDoc on Wednesday 23 August 15:26
Edited by PhysDoc on Wednesday 23 August 15:26
From those measurements you can tighten the squish clearance .020" or thereabouts. This will also improve quench as you have flat top pistons. Your c/r will increase slightly but will have improved the combustion efficiency.
I know you want to lower your c/r but that's not going to be easy. You could nibble away the edges of the quench pad in the head and you could maybe machine a shallow dish in the pistons. You'll need to see how thick the crowns are as the advert doesn't show it. Or buy pistons that have a dish in them assuming you haven't already bought yours. Those are available.
Are your rod ends 21.008 mm?
Deck clearance is from the piston crown to the deck of the block. It's a minus or plus number depending on whether the piston is below the deck or above the deck. It can also be zero if the piston is flush with the deck.
I know you want to lower your c/r but that's not going to be easy. You could nibble away the edges of the quench pad in the head and you could maybe machine a shallow dish in the pistons. You'll need to see how thick the crowns are as the advert doesn't show it. Or buy pistons that have a dish in them assuming you haven't already bought yours. Those are available.
Are your rod ends 21.008 mm?
Deck clearance is from the piston crown to the deck of the block. It's a minus or plus number depending on whether the piston is below the deck or above the deck. It can also be zero if the piston is flush with the deck.
Increase it!!!? Blimey! Lol. I've just put some numbers into my spreadsheet, and I reckon with the piston 20thou off the head I'll be getting nearly 15.5:1.
40 thou squish gives 14.2.
How rare are Buick 300 heads and how much work will they be to fit if I retain the 56cc chamber volume.
The rods I'm looking at are bushed for the pistons.
40 thou squish gives 14.2.
How rare are Buick 300 heads and how much work will they be to fit if I retain the 56cc chamber volume.
The rods I'm looking at are bushed for the pistons.
PhysDoc said:
A question for cylinder head experts
I'm planning a new engine build for my Chimaera based on a rod/stroke/piston combination that will give me a static compression ratio in excess of 13:1 using composite gaskets and early 36cc heads. The pistons are forged flat tops. I know I can bleed the compression off with a wild cam, but even so, I still think this is too high and would rather it was around 12:1 for the cam I want to use.
What is the absolute maximum that the combustion chambers can taken out to without radically altering the shape or removing the squish band.
Why would you plan a build...with a compression that you believe is too high ?I'm planning a new engine build for my Chimaera based on a rod/stroke/piston combination that will give me a static compression ratio in excess of 13:1 using composite gaskets and early 36cc heads. The pistons are forged flat tops. I know I can bleed the compression off with a wild cam, but even so, I still think this is too high and would rather it was around 12:1 for the cam I want to use.
What is the absolute maximum that the combustion chambers can taken out to without radically altering the shape or removing the squish band.
Would it not just be more sensible to plan the build...with a compression you can use ?
And what fuel are you using ? What application ?
Because the crank, rods and pistons are on ebay, and at the moment they are an absolute steal. Although there are 5 days to go yet...
The application is for a street car with occasional track use. I'll use 99 ron fuel like shell v-power. I have a bid on, but not so much that it would hurt if I could not get the combination to work.
The application is for a street car with occasional track use. I'll use 99 ron fuel like shell v-power. I have a bid on, but not so much that it would hurt if I could not get the combination to work.
They're a steel because maybe somebody screwed up. High compression can work if the engines efficient. If you don't think you can make it work then I wouldn't bother with it.
Buick (63/64) 300 heads have 54cc chambers but are poorly cast. The rear water jackets are usually corroded at the deck level from sitting in a scrap yard for years. Also the valve sizes are different to a rover. Iirc the exhaust is larger and the inlet's smaller but it's been a long time since I used them. The ports are taller and on one of them the short side radius is shallower. Think that may be the exhaust port. They will get your compression sorted out but will need an expensive refurb. They are over 50 years old.
Lastly, if you buy the ebay kit, are you sure the piston pin bosses will clear the crank counterweights at bdc? Be a bugger if they don't.
Buick (63/64) 300 heads have 54cc chambers but are poorly cast. The rear water jackets are usually corroded at the deck level from sitting in a scrap yard for years. Also the valve sizes are different to a rover. Iirc the exhaust is larger and the inlet's smaller but it's been a long time since I used them. The ports are taller and on one of them the short side radius is shallower. Think that may be the exhaust port. They will get your compression sorted out but will need an expensive refurb. They are over 50 years old.
Lastly, if you buy the ebay kit, are you sure the piston pin bosses will clear the crank counterweights at bdc? Be a bugger if they don't.
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