Moparts
Low deck build?
Posted By: supercomp
Low deck build? - 09/10/09 11:00 PM
Could you build a low deck using a k1 4.375 stroke, 6.480 k1 chevy rod, and a Diamond 1.30 pin heightt
without having piston to crank issues. We already have a machined 400 block with a 9.970 deck.
Am I grabbing at straws and should just forget about it? Have B1 heads.
Posted By: Cab_Burge
Re: Low deck build? - 09/10/09 11:52 PM
I have a 400 block with a 4.300 stroke cranksahft with 2.200 rod journals, CAT 6.800 long rods
with .990 wrist pins in Ross custom 22.0 CC dished pistons for pump gas
works fine, has lasted a long time (going on six years of strip and street use)so far
Posted By: cudabin
Re: Low deck build? - 09/11/09 12:20 AM
I think you need to machine down the counterweights to clear the piston skirt with that short of a rod...
This is possible as you have to reduce bobweight anyway with a short piston and lightwieght rod!
Go for it...
Arnie
Posted By: gregsdart
Re: Low deck build? - 09/11/09 01:05 AM
My 4.15 stroke with 6.535 rods, and 1.30 pistons pulled the skirt a LONG way out of the bottom of the bore. Your combo will go .1125 further out the bottom, and most race motors stop at a 4.25 stroke in that block. Before proceeding with this, I would set the piston at the lowest point in the bore it will run at and carefully mark the skirt that is exposed, and see what the piston manufacturer has to say. The problem is you most likely need that 1.3 compression height for the B1 heads, right? I don't know if you could go shorter, but doing anything to get that piston up the bore is going to help.
Posted By: supercomp
Re: Low deck build? - 09/11/09 04:44 PM
yeh, 1.30 is it.. doesn''t sound viable. thanks for the info.
Posted By: MRMOPAR622
Re: Low deck build? - 09/11/09 11:46 PM
Could you use a 4.25 crank with 6.57 rods with the piston compression height at 1.300? I have the 6.57 rods and 1.30 pistons now with a 4.15 crank.I guess its just wishful thinking but I would be very happy if it would work.
The finish deck height is 9.965. If the 1.30 pistons would not work is there another that would? The chamber is 60 and the CR is 15-1 would like to keep the CR in the 15-15.5. THANKS
Posted By: 440Jim
Re: Low deck build? - 09/11/09 11:53 PM
This is the calcs I did before. You can put your numbers in to make some conclusions, depending what you are comfortable with for clearance, etc.
Quote:
As far as counterweights hitting the piston at the bottom of the stroke, the typical problem is the piston pin boss, ie metal below the piston pin. This thickness varies a lot from one piston design to the next. My Ross 99496 pistons have 0.150", Wiseco K296A35 have 0.220", my Venolias have 0.180" (see attachment). Everything must be checked at assembly for clearance, but this is the math:
CWmax = Counter Weight max dia
Pthick= Piston thickness below the pin
Pin = Piston pin dia
Rod = Rod Length
CWmax = 2(Rod - Stroke/2 - Pin/2 - Pthick - Clearance)
For example:
CWmax = 2(6.535 - 4.25/2 - 0.990/2 - 0.180 - 0.075)
CWmax = 2(6.535 - 2.125 - 0.495 - 0.180 - 0.075 )
CWmax = 7.32" dia
That happens to be the dia of the "cam cut" on a Callies 4.25" stroke crank counterweight for a BB Mopar.
I cut my Callies 4.250" down to 7.14" with a 2185 gram bobweight.
The rest of the counterweight can be larger since it isn't at BDC. Balancing will need to be addressed with those counterweights. It might work, but I like the 6.535" rod for that.
For yours, you might want the counterweight dia at the piston BDC position close to 7.0x dia. And balancing might need heavy metal, depending.
Posted By: supercomp
Re: Low deck build? - 09/12/09 01:17 PM
Can't put the first ring up that high with B1s.
Posted By: 440Jim
Re: Low deck build? - 09/12/09 01:47 PM
The ring position has nothing to do with the crank to piston pin clearance. The numbers you need to plug in are the thickness of the piston below the pin (.180") and the clearance you are comfortable with (.120", .100", .075" etc). Like I said a counterweight dia around 7.0x is what you would need, and balancing may need heavy metal at that dia, so be careful.
I would like a longer rod than you have proposed. Or stick with a known combo like 4.250", 6.535, 1.3x. You may be able to do a 4.300" stroke with a 6.535 rod and the matching piston and deck height.
Posted By: supercomp
Re: Low deck build? - 09/12/09 02:18 PM
Wonder if diamond can make a B1 piston with a
1.25 pin height, then I could use a 6.535 rod.
Thanks for all the help and explanations.
Posted By: gregsdart
Re: Low deck build? - 09/12/09 02:48 PM
You could find out what the max head gasket thickness is that cometic can make and will work well, and that might help. If a .090 gasket will work for instance, you could gain about .050 deck height on the piston. The next question is how much dome can stick out the bore, but I believe if the top ring is at least .050 down from the bevel on the bore you should be ok?
Posted By: RT540
Re: Low deck build? - 09/12/09 06:39 PM
Quote:
Wonder if diamond can make a B1 piston with a
1.25 pin height, then I could use a 6.535 rod.
Thanks for all the help and explanations.
I am going to buy 1.25 pin H. for my B1 orig. heads.
The pin just needs to be in the oil ring land, and then you have a bottom steel ring to support the oil rings.
Posted By: RT540
Re: Low deck build? - 09/12/09 07:02 PM
Here´s a B1 Venolia piston I borrowed from a friend.
This one got 1.22
Posted By: cudabin
Re: Low deck build? - 09/13/09 02:58 AM
How short of a piston compression height is too short for a race motor?
My 540 has 4.25" stoke X4.5" bore w/ 6.635 Alum rods and a 1.205" compression height piston.
Too short?
Arnie
Posted By: 540dust
Re: Low deck build? - 09/13/09 04:42 AM
My low deck 540 is 4.25 stroke X 4.5 bore, a 6.76 rod and a piston CD of 1.06.
Posted By: supercomp
Re: Low deck build? - 09/13/09 01:52 PM
Thanks guys. I think it will work. What ring pack? Race only dragster.
Posted By: 79_W200
Re: Low deck build? - 09/13/09 03:58 PM
Quote:
My low deck 540 is 4.25 stroke X 4.5 bore, a 6.76 rod and a piston CD of 1.06.
What block? That is a short piston,do you think it will last?
Posted By: 540dust
Re: Low deck build? - 09/13/09 07:01 PM
Indy maxx low deck block. I was running 1.09 since 2001, I went to a 1.06 cd piston in 2006 when I went to 4.25 stroke. I now have 500 runs on the 1.06 pistons. I had close to double that on the 1.09's. Top ring is .200 down from the deck of the piston.
Posted By: sr4440
Re: Low deck build? - 09/14/09 12:44 AM
I have 1.10 compression height with my B1’s. No problems here
Joe
Posted By: supercomp
Re: Low deck build? - 09/14/09 12:48 PM
Do you have the specs on the ring positions? And how deep were the notches? Thanks
Posted By: 540dust
Re: Low deck build? - 09/15/09 02:43 AM
Rings are .064 .064 .218 the top ring is .200 down second is .150 from that and the oil ring is .085 down from that. Int pocket is .265, exh pocket is .245 both 15 degrees. They are J&E custom flat tops and the job number is 499577, piston part number is #241700, the bore is 4.498 cd is 1.06,.990 x 2.93 pins, 514 grams.