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Discussion Starter #1
Who make's thinner headgaskets for the n/a?

If not thinnner who makes thicker cause if they make thicker i probaly can get athinner one made for me. Thanks
 

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What's the objective here? Raising the compression ratio? The thinnest gasket I've seen is 0.7mm by HKS back in the eighties. Milling the head (clearance?) is an option. Domed pistons probably work best.
 

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Discussion Starter #3
I need to raise my compression rati to 12:1 i want to do it without milling the block .whats the specs on the hks gasket that lowers compression how many mm? . and to do 12:1 to go with my racing cams/ what what mm do i need to use.im going for the cheap way to increase compression right now so if want to lowr the compression back down if i do a single turbo i can. unlike milling the block, changin the pistons. I know its do able i just need to know what mm headgasket i need. . Thanks for the help. Xdreamer


im running 10:1 now
 

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1)Correction it's milling the head, decking the block. 2)The compression lowering headgasket is 3 mm thick & I think it lowers compression to about 9:1, max for a turbo, but less lag. 3)I doubt you can get more than .5 increase going from a 1.0 to a .7mm headgasket or no gasket on a "dream machined" engine.:rolleyes: You need to make a choice: hi-comp or turbo. Once you buy parts &/or have machine work done. That should be it. Review your performance/budget goals.
 

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Discussion Starter #5
the gasket you are talking about lowers our compression down to boost friendly 8:1 might be 8:5:1 anyways what mm gasket should ise to get up to 12:1 i dont want to have to deck the block cause i might go turbo down the road but right now i want t make this n/a really fast without the turbo. i like these type of projects. Thanks
 

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Check with the real experts, but I don't think a thinner head gasket is going to take you from 10:1 to 12:1. Any gearheads care to elaborate on this?:arcade:
 

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Discussion Starter #7
i am pretty sure i can do 11:1 with a headgasket im still researchin but i am pretty positive. any one want to elaborate or have any experiance. im going 11:1 so i can still have it as a daily/weekend driver. it should yield something %8 percent more tq and hp but with all the mods im doing i need every h.p and dont want to have to run on 100 octane to be able to drive the car .
 

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These are very crude calcs, but every mm in headgasket thickness equals roughly .5 point of compression. So to go from 10:1 compression to 11:1 compression, you would need a headgasket that is 2mm thinner than the stock gasket. The stock gasket is about 1mm thick.
 
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HKS make a .5mm stopper for the Acura, but I don't know if there is one for a Supra. That's a very, very thin gasket, especially for a stopper type. The old rule of thumb was one for one in compression and tenths of an inch. That is, if you are at 9:1 and had a milled 2 tenths off, you could get to 11:1. Since 2.54 mm = one tenth of an inch, and the stock Toyota gasket is 1mm, without milling the head I don't think there is any way you can get to 11:1.
 
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DaveH, I missed your reply, but I think 2 or 2.5mm per 1 unit of compression is close enough!
 

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Thanks Dave, I thought his pursuit was a bit of a reach. So using these "rough" estimates,he would need a -2mm head gasket,to acheive this. His other option is a used, refurbished head to mill, putting the original back on with a turbo kit. Whew!
 

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Discussion Starter #13
so the headgaske tthat make the car 8:5.1 wheni want to turbo it is how thick? I am still tryin to figure if i can do this . i might pick up another head but it might not be cost affective. so the stock gasket is 1mm on my my impala it had a .050 gasket and i put in a .060 gasket? i know i raised the compression half a point. does that make sense i have to double check exactly. i am going to get 11:1 someway or another. do you think i could mill the head without taking it off or would i just be asking for problems doing so. Thanks for the post i am almost done figuring how i am doing this . Thanks Brett

does anyone know what mm the lexus is300 headgasket is?
 

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Did you say mill the head wiyhout taking it off? Hell No! Typo, ok? 11:1? One way- higher compresion pitons. Next way, mill the head (valve clearance?). Deck the block(clearance?) Not impossible, but hey, you don't get something for nothing.;)
 
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Xdreamer, if you increased the thickness of the head gasket, you would have lowered the compression on the Chevy. If you have 9:1 on your NA with a 1mm gasket, you might want to go 2mm if you plan to turbo. Remember there is some crushing if you don't go Metal, but if you spend the money I would think 2mm stopper-type should serve you well and prevent a BHG.

You have to take the head off to mill it. You may want to resurface the block deck at the same time.
 

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Discussion Starter #16
Could i just get made up a .20 or .50mm headgasket to higher it a degree to like 10.5 or 10.8 to 1?

Thanks for the help and for my impala i put i thinner headgasket i had .60 i puta .50mm

so what would that .10 on a inch eqaute tocompression on my impala? would that raise it half a point or just .1? im still trying to get all this down. Thank for the help ~Brett
 
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Compression example, rather long

Xdreamer, sorry I misunderstood your gaskets on the Chevy. Yes, obviously dropping it .1mm would raise the compression. How much? I don't know because the rule-of-thumb is exactly that...only an aid to get you started.

If you have an engine with a short stroke and a big bore (called over-squared) that is say 3 litres and you shave .1 inch off the head (or thin the gasket which has the same effect) you raise compression more than in a 3 litre engine with a long stroke and small bore. For the MKIII engine (7M) the bore is 83mm and stroke 91. The compression is 9.2:1. The MKIV engine (2JZ) is square, with both bore and stroke at 86, and compression at 10:1. The HP for the 7M is 200, and 220 for 2JZ. The torque went from 188lb-ft to 210. (I’m mixing metric and Imperial, but most people don’t think in kilowatts of power for engines, even in Europe they use a metric horsepower!)

To calculate what happens when we take 2 mm off the head, we need to do some simple volumetric calculation. I’ll use the MKIII here. Since the Volume of a cylinder is given by V=pi*r**2 * H (ignoring head shape), for the 7M you would have (83/2**2)*3.14* 91, or 492,365.907 cubic mm, or 492.37 cc for one cylinder; times six gives 2954.19 cc for the total engine, which is what Toyota claims. That means that at 9.2:1 the volume of one cylinder is compressed from 492.37 cc to 53.52 cc. Since the cross-sectional area of the cylinder is constant at (83/2)**2)*3.14 or 5.41 sq-cm, the height of the compressed cylinder is 53.52/5.41 or 9.89 mm. Now take 2 mm off the head, effectively lowering the compressed height to 7.89. Working backwards, we have a compressed volume of 5.41*7.89 or 42.69 cc. However we changed the stroke of the engine by the same 2mm, so the uncompressed volume of our milled cylinder went from 492.37 to 481.54 based on (83/2**2)*3.14*89. Consequently, our new compression ratio is 481.54/42.69 or 11.28:1. A significant compression increase!

Diesel engines with their 20:1 compression don't even vary the amount of air each stroke. Power is controlled strictly by the amount of fuel supplied. Interestingly enough the turbocharger was invented to use with diesel engines in 1905 exactly because of this lack of throttle air control. They were adapted to aeroplanes prior to WWI not for speed, but simply to keep the manifold pressure up to a sea-level equivalent as they became capable of flying higher. In fact, that is their primary purpose on aviation engines even today. But I digress....

Another consideration is the torque applied to the head gasket. If you follow Toyota's 58 lb-ft recommendation for a non-metal gasket, you have a lower compression than if you go to 72 lb-ft, because the higher torque will compress the gasket slightly more. The temperature range of the spark plug can also slightly change the compression because the tip reaches farther into the cylinder depending of the plug's heat range. These things have a greater affect as the compression ratio gets higher.

Could you turbo an 11:1 engine? Sure, but you will run into pre-combustion problems. I would say if you plan to turbocharge, you need to lower the compression so the turbo has room to work. There are lots of write ups on other threads here, on the SOGI form, supras.com, or MKIV.com. On the other hand, if you plan to stay NA or put on a Roots-type supercharger that has a fixed output, 10.5:1 is workable.
 

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Discussion Starter #18
when you say 2mm do you mean .2mm? in your calculations?

And im not worried about turboing the car yet. worse case i will buy anew head when that days comes. Thanks Brett
 
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The figure is 2mm, which is just under one-tenth of an inch. 25.4 mm = 1 inch. You could do the calculation with 0.2mm, but that's only 8 thousands of an inch, hardly worth taking the head off.:)
 

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Thank you. Long, just above my head, but not too much. Toysport mentions high compression for the 7M (12.5:1), but I have yet to see one on the board. I think a high comp n/a could generate 260-300 hp 240-260 tq. If this could be done for 4-5k it might be worth it. Any comments Yonaga? Where's the all motor Supras out there? Put this engine in a mkii?:p
 
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