FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: Joey120373 on February 17, 2021, 06:09:40 PM
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It’s time to order some pistons for my engine.
I’ve been talking with Jay about pistons for his heads.
His design currently has gas ports.
Just curious if there were and pros or cons for having them on a 10.7 to 1
“Warm” street engine?
The engine may get a little rowdier cam down the road ( 6500 - 7000 )or so
But for now should peak about 6000.
Right now I’m looking at a dished version of the same piston Jay is using in his dyno mule.
Just wondering if I should keep the ports or omit them.
Thanks
Joe
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You can do lateral gas ports. I don't like running verticals on street vehicles, easy to clog the holes up.
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Thanks Brent, that’s kinda what I thought .
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We can do either vertical, lateral, or no gas ports. I've actually been surprised at how long the vertical gas ports last on the street, it's not like they close up in 1000 miles or something. After teardown post Drag Week a couple times the holes are still wide open. I'll bet they'd go 10K+ miles before any issues.
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We can do either vertical, lateral, or no gas ports. I've actually been surprised at how long the vertical gas ports last on the street, it's not like they close up in 1000 miles or something. After teardown post Drag Week a couple times the holes are still wide open. I'll bet they'd go 10K+ miles before any issues.
Agree - I have had them do pretty well. I think a lean and clean tune up helps a lot
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We can do either vertical, lateral, or no gas ports. I've actually been surprised at how long the vertical gas ports last on the street, it's not like they close up in 1000 miles or something. After teardown post Drag Week a couple times the holes are still wide open. I'll bet they'd go 10K+ miles before any issues.
Agree - I have had them do pretty well. I think a lean and clean tune up helps a lot
I wouldn't mind verticals for guys who keep a real close eye on their tune, but a lateral is a little more forgiving.
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I'll be ordering custom pistons but not for some time yet. In the context of this thread what ring thickness are will looking at?
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Context? What is your long term usage? For street, I would not go below 1.0/1.0/3.0, but for long term, I would also consider 1.5/1.5/3.0. Joe-JDC
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Context? What is your long term usage? For street, I would not go below 1.0/1.0/3.0, but for long term, I would also consider 1.5/1.5/3.0. Joe-JDC
Exactly my point. My case is pure street car. Lucky to put 3000 miles on in a season. But something like 10years/30,000 miles seems reasonable to me. Guessing that's a 1.5/1.5/3.0 without side porting?
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I run the 1mm/1mm/3mm on the street. The Mahle PowerPak series pistons have been using 1mm rings for a long time. The OEM has gone to 1mm and even .9mm rings.
If the cylinder is straight and round and the finish is correct, then the thinner ring is not a detriment to ring seal. It's actually better because pressure is force divided by area.
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Gasports always increase power as they use cylinder pressure on top of and behind the top ring to improve seal. Because of this they do shorten ring life to some extent. It is more beneficial on rings thinner than 1/16th.
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We use quite a few Mahle rungs at 1.0-1.0-2.0mm
They seem to work very well.
Not sure I'd recommend them to guys doing a bottle brush hone though...
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I’m in the narrow ring camp.
So I’ll ask for lateral ports then. I plan on making sure this is tuned well and stays that way.
Thanks for all the advice.
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Ive been in touch with Jay, pistons should be getting ordered Monday.
So one last thing that is nagging me, and Ive asked the question before, in a more general sense, how much compression should i shoot for?
In the past, the rule of thumb was 9.5 or so for iron heads and pump gas, aluminum heads let you go to 10 or so.
Since i live at 4500 feet, i figured 10.5 was pretty safe still, and ended up at 10.7 with a 30cc dish.
But its nagging me that I may be being to conservative. I can give the cam numbers if Brent is ok with it, but its not a small cam.
With as much quench as i can get, and the modern combustion chamber, am i leaving HP on the table or is ~10.5 to 1 a good choice?
Figured i would ask before the order went in.
I
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Here's my two pennies:
Your altitude would probably let a little more compression work for you. If you have junky gas there or if you plan on moving to a lower altitude some day, then you may want to stay where you are. But to be honest, the difference between 10.7 and 11 or 11.25 will be negligible anyway.
A few notes on the cam stuff:
DCR is a nice tool to use when you're concerned about what you can get away with on pump gas. However, when you get into larger cams for big displacement engines, the DCR is going to be low and there's not much you can do about it. You could potentially advance the poop out of it, but you'd be probably be at <100° ICL on some cams. Does it matter? No. I only use DCR as an upper limit tool, not a lower limit tool.
Also, engines can have over 100% volumetric efficiency. When that happens, DCR kinda goes out the window and static compression is what the engine sees because the cylinders can be "overfilled". To dumb that statement down, you can't just keep bumping the compression ratio up and think that you can just add more cam to run on pump gas. "I'm at 14.5:1 compression but the cam is 350° advertised duration, so it should run on 93 octane!"
You have a heavy vehicle but you also have a big cubic inch engine with modern cylinder heads that will make a lot of power. And again, the altitude helps you. 11:1 seems safe to me.
Jay and I are working on another build for another gentleman that has roughly the same specs as you. His cam and your cam will be extremely close to each other. I am having his cam ground now and it will be at Jay's in a week or so for testing with the crossram EFI manifold, so Jay will have the cam card for it.
You asked about the 1.95:1 ratio rockers in your email. With these hydraulic rollers, I can set them at around .660-.680" lift with a 1.76, so I'd aim for that. Valve spring and lifter requirements change when you get into more aggressive lobes with a lot more lift. We are making leaps and bounds on camshaft development for the FE, but most FE's will not have extremely light valve weights, like you see in an LS, SBF, SBC, etc. You can get away with a lot more when you're running 7mm valve stems, hollow stem valves, or even titanium valves, but when you're looking at large diameter, long length stainless valves, the lifter/spring package requirements change.
I urged Jay to go to the larger rocker ratios so that we can run some standard core solid roller camshafts instead of paying $$$$ for special cores. We ran into this on the cam I spec'd for his dyno mule and if he had used a 1.8, 1.85, or 1.95 rocker, we could have ran a lot more lift.
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Thanks Brent.
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Hey Joey120373.
Can I ask what your final piston order details were? I am looking to grab a set of pistons too and have to answer the same questions. TIA!
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I have heard some feedback on the lateral gas port rings, and the consensus so far seems to be very positive. Better even than the ports in the piston lands. Ring seal is better with less twist, and cylinder wear is better for leak down tests, etc. Seems the rings don't tend to buckle with compression as bad with the lateral grooves in them, and they run cleaner. Joe-JDC
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Joe ,
I saw the data Lake Speed jr gave to us from a test at Shaver Specialty on a current 410 alcohol sprint car engine. The increase was about 6 HP MAX in the 4,000+6,000 rpm range and was about the same at higher RPM to a gas ported piston. This was against a lateral gas ported piston NOT a vertical gas ported piston. Yes there is a power difference. "I" do not see how a ring with varying thickness can stay "flat" when subjected to heat like that of combustion heat.
There is a DISTINCT advantage to using this ring design when "gas ported pistons" are not allowed. ANY time you put cylinder pressure behind a ring you will have better seal and more HP.
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. Hey Joey120373.
Can I ask what your final piston order details were? I am looking to grab a set of pistons too and have to answer the same questions. TIA!
Guagster, I will try to look up the build sheet on the pistons, I tried to respond to your PM yesterday but it did not go through.
I am currently working 16 hour shifts at night with no cell service and very limited internet, so it may take a day or two for me to scrounge it up and send it .
If I recall, my pistons are pretty much the same as what Jay has in his motor, except that they have a 30cc dish to get the CR down for pump gas.
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. Hey Joey120373.
Can I ask what your final piston order details were? I am looking to grab a set of pistons too and have to answer the same questions. TIA!
Guagster, I will try to look up the build sheet on the pistons, I tried to respond to your PM yesterday but it did not go through.
I am currently working 16 hour shifts at night with no cell service and very limited internet, so it may take a day or two for me to scrounge it up and send it .
If I recall, my pistons are pretty much the same as what Jay has in his motor, except that they have a 30cc dish to get the CR down for pump gas.
It's very much appreciated. My 390 based build (460 CI stroker) is calculated to be 10.4 : 1 with a 21cc dish. But I still have to confirm my target deck height etc... so very much a keyboard exercise.
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Bore: 4.350”
- Stroke: 4.375”
- Pin Diameter: 0.990”
- Rod length: 6.700”
- Block Deck Height: 10.150”
- Head Gasket: .041”, 4.400” bore
- Cylinder Head: FE Power or standard FE
- Combustion Chamber Volume: 69cc
- Static Compression Ratio: 10.77:1
- Cam Specifications: 255/265 @ .050”, 0.800” Lift, 117 LSA
- Gas Ports: Lateral
- Top Ring: 0.9mm steel
- Second Ring: 0.9mm Napier
- Oil Ring: 3mm, standard tension
- Pins: Standard pins for 0.990” diameter, fitted to pistons
These are the notes from the invoice, the ring thickness did change though. Evidently with my bore size, .9mm rings are not available, so they went with .041 for the top and second ring.
I ordered them in late February, so I suspect they should be arriving any time now.
That will be a landmark moment as I can get the machine work started on the short block.....
Need to get a hold of Brent again and get the cam and lifters on the way.
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Gotta have a machinist that's really on top of things to use a .9mm ring. A .043" top ring would be 1.09mm. You're not losing anything power-wise, it's really diminishing returns after 1.5mm, unless you're looking for low single digit horsepower gains.