Twisted Wedge heads questions (2)

Scorcher2005 · Jul 27, 2005

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?

rflow50 · Jul 27, 2005

I have the same heads, they don't use the stock spark plugs. Contact Trick Flow Tech Line and they will tell you the part number for the plugs.

Scorcher2005 · Jul 27, 2005

darn :-/

can anyone chime in on the compression ratio?

rflow50 · Jul 27, 2005

Well, firstable what kind of pistons do you have. Comprression ratio probably is going to be 9/8 to 1 or 10/1. thanks.

nmcgrawj · Jul 27, 2005

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.

nmcgrawj · Jul 27, 2005

straight from trickflows' site....

AC FR3LS
Autolite 3924
Champion RC9YC
NGK-FR5

Grn92LX · Jul 27, 2005

Yep, 3924's.

With a 61cc head on a stock block and stock pistons, if your lucky you'll have 9.2:1 compression at most. I would use a 1011-2 head gasket as its a .039" compressed thickness gasket.

Scorcher2005 · Jul 27, 2005

thanks for the plug numbers

and the pistons remain stock (for now)

vristang · Jul 27, 2005

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.

Scorcher2005 · Jul 27, 2005

vristang said:
Head Gasket Diameter (in)_________4.103

4.145

the thickness is correct and all the other measurments seem accurate. all i didn't know is that the piston is only 3.8" wide to fill a 4" bore. I thought it would be closer than that.

vristang · Jul 27, 2005

Scorcher2005 said:
4.145

the thickness is correct and all the other measurments seem accurate. all i didn't know is that the piston is only 3.8" wide to fill a 4" bore. I thought it would be closer than that.

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.
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.

Scorcher2005 · Jul 28, 2005

thanks. so w/ 9:1 cr, i can run just 87 octane and be fine, right?

QDRHRSE · Jul 28, 2005

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.

Scorcher2005 · Jul 28, 2005

i dont know what timing ill be at since ill have a new h/c/i. but in the past i only sprayed on premium fuel w/ 10* timing (instead of my normal 14ish). But its actually been cooling down here lately.

Scorcher2005 · Jul 31, 2005

i went to autozone to get the autolite 3924s. He showed me the box and they are double platinums. Is that what you all run? I didnt want platinums and went w/ a champion copper alloy plug.

nmcgrawj · Jul 31, 2005

Scorcher2005 said:
i went to autozone to get the autolite 3924s. He showed me the box and they are double platinums. Is that what you all run? I didnt want platinums and went w/ a champion copper alloy plug.

They are copper plugs although autolite has platinum and iridium now. 3924=copper plug

2000xp8 · Jul 31, 2005

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.

Scorcher2005 · Jul 31, 2005

nmcgrawj said:
They are copper plugs although autolite has platinum and iridium now. 3924=copper plug

then why would the box say platinum, actually it said double platinums

Grn92LX · Jul 31, 2005

Scorcher2005 said:
then why would the box say platinum, actually it said double platinums

Because the parts kid gave you the wrong set. I just bought a set of 3924's the other day. It was like $10 for all 8 of them. Return them and find someone who knows what their doing.

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