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Discussion Starter · #1 · (Edited)
What's the minimum piston to valve clearance for a big chevy with a max rpm of 8000 rpm's and steel rods? The 8000 rpm is with engine alone, no nitrous, and then what is the minimal clearance with say a 200hp level used, same rods. Dart 325 heads with 119cc chambers and dome heigth of .625 on the pistons? With nitrous useage, there will be a gear change before running it.
Thanks in advance.:)
 

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I run .040 on my 565 and the odd number pistons all kiss the head but with no issues. It also has a 250 difuser plate tune up on it. I ran it at .050 and nothing touched at all.
 

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Your meaning piston to head I assume right McCoy?

A general standard is around .080 intake and .100 exhaust. Theres always exceptions to the rule though.
 

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Discussion Starter · #4 ·
Well, since the head basically doesn't move, it would be the valves, and since the valves run after and run away from the pistons during the timing events, I wanted to make sure of the acceptable distance between the intake and exh valves to the flycutouts of the pistons. I just used clay and spun the engine over twice and took measurements and I have .200+ on both valves, so I should have more than enough clearance, yes, that is just shy of .250 or a 1/4 of an inch of thick clay!:supz: this was measured with a .053 thick MLS gasket and I wanted to go to a .041 thick MLS gasket, this is why i was asking. Thanks for the help guys.:)



Your meaning piston to head I assume right McCoy?

A general standard is around .080 intake and .100 exhaust. Theres always exceptions to the rule though.
 

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Hey John, still using the 1150 I sold you?
Stainless or titainium valves?
If you run close and don't keep up on valve springs you could have issues. If you are still turning it 8000 + and are not using ti valves you really should upgrade. BUT the margin on a ti valve is a lot thicker so you will lose clearance.
.090 absolute minium exhaust
.070 absolute minimium intake
If anything goes out of whack like spring pressure dropping from abuse you can crash.
With that kind of room you could get a 1.8 rocker on the intake for about another .040 of cam lift along with the gsk change..
 

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Your meaning piston to head I assume right McCoy?

A general standard is around .080 intake and .100 exhaust. Theres always exceptions to the rule though.
Yep I misread the question somehow. Sorry. I ran .090 on the exhaust and .070 intake with checker springs so in reality it was more.
 

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Its all about your springs, thats your best weapon on exhaust valve meeting piston. RPM level is second weapon rev limiter, alum rods require alittle more room steel rods alittle less but stretch as well at high rpms. BBC,s i run as close as .045 intake and .075 on exhaust at up to 9500 rpms. but thats with springs that will cost ya but you have to ask yourself pay now or pay big time later. Less rpm less worry with springs. Always check em. Any spring can break and theres no chance to save a valve in a H/Pro. motor with any amount of clearance with any kind of serious compression. Forge pistons i always preach, hands down. Guys are correct .100 to .125 basic exhaust .080 to .100 intake will kept you out of trouble. The more the better for alittle over reving OPPS.
 

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Discussion Starter · #10 · (Edited)
You guys are crazy, "put a bigger cam in it":p

I have PSI Triples of the 1.62 diameter if I remember, so do the math on them springs and you will find out they are not cheap real fast, and I found only one so far with a inner spring coil broke, so I caught things just in time. One thing I did notice when I pulled my engine apart was scuffing on my pushrods, and I know they are deflecting, but man, they are Manton's and the next size up is the 7/16 diam. I have a brand new set of 7/16 still, and can't use them unless I buy offset lifters!!

I tell ya, I need to get rich real quick if I am going to continue to play this racing game:rolleyes:

Hey bad news, a matter of fact I still am, and I tried a QFT 1250 and I didn't pick any mph or et to speak of, but a nice carb nonetheless. Yeah, the 1150 works great, and I have a 1050 coming to try on the dyno after I rework my head ports for the gasket matching of the new Brodix intake I am going to try out, I need more torque to help get my pig moving quicker, so I am looking for some lower rpm torque numbers when testing it. I have a feeling the Brodix intake will help a lot, especially with nitrous so time will tell all. The same valves that Dart puts in there heads, the stainless steel ones.
I already have a 1.75 ratio on the intake, and the std. 1.70 for the exh. and I am right under .800 lift on the intake, around .760 exh. Yeah, I could always spend more money, but, it's just not here, and I want to travel this year to some of the NMCA events and race at Milan's Heads up races this year too, and it all takes money!!!:mad: root of all evil:rolleyes: I just want to get the engine back together, make some races this year and then the 540 starts and I am targeting 900-950hp and over 700ftlb.s of torque, and then the spray comes in again;) Chassis is maxed out at 8.50's so that is my limit and I only want 8.80's at current time and I will play in that range for a while.

I am accepting any donations also for a larger cam, but a 505" engine with Dart 325's can only take so much you know!!!;)

Thanks for the info guys and it looks Like I have plenty of room to play in. I keep close tabs on my springs also and check the psi's alot, so if I can keep up with the springs all else should keep working. Knock on wood:cool: Later guys, good luck this year too to all of you.

ElkyJohn



SHIT.....put a bigger cam in it............if you have that much......lol
 

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You guys are crazy, "put a bigger cam in it":p

I have PSI Triples of the 1.62 diameter if I remember, so do the math on them springs and you will find out they are not cheap real fast, and I found only one so far with a inner spring coil broke, so I caught things just in time. One thing I did notice when I pulled my engine apart was scuffing on my pushrods, and I know they are deflecting, but man, they are Manton's and the next size up is the 7/16 diam. I have a brand new set of 7/16 still, and can't use them unless I buy offset lifters!!

I tell ya, I need to get rich real quick if I am going to continue to play this racing game:rolleyes:

Hey bad news, a matter of fact I still am, and I tried a QFT 1250 and I didn't pick any mph or et to speak of, but a nice carb nonetheless. Yeah, the 1150 works great, and I have a 1050 coming to try on the dyno after I rework my head ports for the gasket matching of the new Brodix intake I am going to try out, I need more torque to help get my pig moving quicker, so I am looking for some lower rpm torque numbers when testing it. I have a feeling the Brodix intake will help a lot, especially with nitrous so time will tell all. The same valves that Dart puts in there heads, the stainless steel ones.
I already have a 1.75 ratio on the intake, and the std. 1.70 for the exh. and I am right under .800 lift on the intake, around .760 exh. Yeah, I could always spend more money, but, it's just not here, and I want to travel this year to some of the NMCA events and race at Milan's Heads up races this year too, and it all takes money!!!:mad: root of all evil:rolleyes: I just want to get the engine back together, make some races this year and then the 540 starts and I am targeting 900-950hp and over 700ftlb.s of torque, and then the spray comes in again;) Chassis is maxed out at 8.50's so that is my limit and I only want 8.80's at current time and I will play in that range for a while.

I am accepting any donations also for a larger cam, but a 505" engine with Dart 325's can only take so much you know!!!;)

Thanks for the info guys and it looks Like I have plenty of room to play in. I keep close tabs on my springs also and check the psi's alot, so if I can keep up with the springs all else should keep working. Knock on wood:cool: Later guys, good luck this year too to all of you.

ElkyJohn
By the way whats your current seat and over the nose spring pressures????? more infor on 505 compression? quench distance? internal or ext crank? cam at .050? valve size just some thoughts.
 
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