I am in the process of my h/c/i swap (so far i have the upper intake off and fuel injectors unpluged and alt out.) Any ways, i have some questions about the heads. What will the new compression ratio be with them on (they have the 61cc chambers)? Secondly, will they use stock spark plugs, such as Autolite 25s?
Twisted Wedge heads questions (2)
- Thread starter Scorcher2005
- Start date
nmcgrawj
Advanced Member
I dont think it will be 10:1 with 61cc chambers....but then again im not sure on what it will be. I want to say mid 9's:1.
The spark plugs you need, atleast the autolite plug is 3924 or 3925 if you dont want to run the colder plug.
The spark plugs you need, atleast the autolite plug is 3924 or 3925 if you dont want to run the colder plug.
nmcgrawj
Advanced Member
Here's what I come up with...
Cumbustion chamber size (cc)______61
Piston Diameter (in)______________3.8
Height to 1st Piston Ring__________0.25
Deck Height Clearance (in)_________0.012
Head Gasket Thickness (in)________0.039
Head Gasket Diameter (in)_________4.103
Dish Volume of Piston (cc)_________2
Stroke (in)______________________3
Piston Bore (in)_________________4
Compression Ratio_______________8.73
If any of these numbers are off let me know and I can run the calculator again. I was just taking guesses at some of them.
Cumbustion chamber size (cc)______61
Piston Diameter (in)______________3.8
Height to 1st Piston Ring__________0.25
Deck Height Clearance (in)_________0.012
Head Gasket Thickness (in)________0.039
Head Gasket Diameter (in)_________4.103
Dish Volume of Piston (cc)_________2
Stroke (in)______________________3
Piston Bore (in)_________________4
Compression Ratio_______________8.73
If any of these numbers are off let me know and I can run the calculator again. I was just taking guesses at some of them.
That 3.8 was a wild (and pretty bad guess). Keep in mind though that this is not the skirt diameter, but the diameter of the piston above the first ring.Scorcher2005 said:
My .030 forged Al pistons measured 3.9895. So I used 3.9595 for your calculation. Your clearance is probably a little tighter than mine, but without measuring the piston I don't know how else to accuratley guess at that value.
I did measure my Fel-Pro head gasket at 4.103, but will used the number you gave me for your head gasket cylinder diameter.
I cannot confirm piston to deck height, piston dish volume, or height to first piston ring for the 302. I left the numbers in the spreadsheet that I measured for my motor.
I also tried to figure cylinder leak down losses. I am not sure how accurate the numbers are with those calculations. If any one has any thoughts I would love to hear them.
Cumbustion chamber size (cc) _____61
Piston Diameter (in) ___________3.9595
Height to 1st Piston Ring _____0.25
Deck Height Clearance (in) _____0.012
Head Gasket Thickness (in) _____0.039
Head Gasket Diameter (in) _____4.145
Dish Volume of Piston (cc) _____2
Stroke (in) _________________3
Piston Bore (in) ___________4
Compression Ratio ___________9.18
Cumbustion chamber size (cc) ____61
Piston Diameter (in) __________3.9595
Height to 1st Piston Ring ____0.25
Deck Height Clearance (in) ____0.012
Head Gasket Thickness (in) _____0.039
Head Gasket Diameter (in) _____4.145
Dish Volume of Piston (cc) _____2
Stroke (in) ________________3
Piston Bore (in) __________4
Blow-By (%) ________________5
Compression Ratio __________8.72
Cumbustion chamber size (cc) ____61
Piston Diameter (in) __________3.9595
Height to 1st Piston Ring _____0.25
Deck Height Clearance (in) _____0.012
Head Gasket Thickness (in) _____0.039
Head Gasket Diameter (in) _____4.145
Dish Volume of Piston (cc) _____2
Stroke (in) _________________3
Piston Bore (in) ___________4
Blow-By (%) _________________10
Compression Ratio ___________8.26
According to my math you can lose almost a full point on your compression ratio at only 10% blow by. When I ran low tension rings is the 408w I measured 20% leakdown. I was down to an effective CR of 7.08
Let me know what you guys think.
QDRHRSE
New Member
If you back the timing off you could use regular unleaded without any problems. Be careful though, this is gonna be one of the hottest summers that we've had in a while. Don't even think of using your nitrous without super- that would be insanity.
nmcgrawj
Advanced Member
Scorcher2005 said:
They are copper plugs although autolite has platinum and iridium now. 3924=copper plug
Check Piston to valve clearance, i know from experience that TW's are NOT safe for all engines. My pistons had to be very minorly notched to get the .080 of clearacne necessary to be safe. Calculating for the HG mine would only come up with .070 of clearance.
In some situations you can use a thicker head gasket, i could not since my heads were made with a receiver groove.
In some situations you can use a thicker head gasket, i could not since my heads were made with a receiver groove.
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