CNC Head Surprise
Thread Starter
Staging Lane
Joined: Aug 2009
Posts: 75
Likes: 0
From: everett, wa
Question: The cars oil pressure drops after driving on the freeway for any period of time. It's fine when I'm actually cruising but once I hop off the freeway and come to a stop it will drop for about a second to 0 then hops right back up. My guess is either the bearings are toast or its a high volume pump with the stock pan.
Dunno. Maybe they started doing that later? I bought mine from LPE 15 years ago and they aren't stamped. The one thing that makes me think it is not from a LPE CNC program is the CNC steps stop around the bowl area.
Thread Starter
Staging Lane
Joined: Aug 2009
Posts: 75
Likes: 0
From: everett, wa
Nope, they are stamped SRP on the underside ive got a pic on my camera at home I'll throw up later. Pistons look pretty different too. Check out the bottom of the dish there is a step on min that isn't completely round as well as a small widows peak right by what i would consider the valve relief portion of the pistons.
Any ideas on what would be the best route to go here im thinking just pull the motor, new pistons and freshen it up....
Thanks for all the responses guys
Thread Starter
Staging Lane
Joined: Aug 2009
Posts: 75
Likes: 0
From: everett, wa
Yup, at the moment its undriveable. I replaced the sensor when I snapped the old one but never tossed a mechanical gauge on it. It's been like that since I bought it tho the oil pressure is normally fine but will drop after coming to a stop if I've been driving for a while or go WOT then stop shortly there after. If i were to pop a few main caps off should I visibly be able to see whether the bearings are fine enough?
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2. As far as the CNC heads/cam car running cam only numbers: There is an unmeasureable difference between one car and it's results and another beyond just cylinder heads. I'd be willing to bet there are MANY heads/cam cars that don't run the numbers that some of the best bolt-on only cars have ran...much less cam only. That is any brand heads/cam cars. Lots of them are 12 second only rides. I have ran better numbers with a 433 bbc with unported cast iron heads (in a bolt on suspension 61 Bel Air than alot of people with aftermarket aluminum headed 496's and 540's in Chevelles, Novas, and Camaros. Combination is everything.
3. I have CNC heads because that is what I got a great deal on and was willing to give a try. I'd have been just as quick to buy a pair of AI 200cc or LE2's....with no real preference between the two. I personally don't care what everyone's arguements are they are both proven performers in my opinion.
4. I have NO hp numbers or time slips (yet) for my CNC headed LT1 to support whether they work well or not, so don't think I'm claiming they are the best. If it's performance is subpar....I can always let everyone blame that on the off the shelf cc503 cam. LOL
OP, before you go buy new pistons I would weigh the cost versus the gain. Yes you will make more power with an optimized compression ratio, but you are talking about the cost of new pistons, rings, and a balance job. I don't have a guess without research what your current compression is, but if you could gain 2 full points and make a whole 4% increase per point that would mean what....maybe 40 HP at best. Not a small amount for sure, but perhaps you could get a portion of that with a slight mill of the heads and a thinner head gasket?
I'm not trying to say it isn't worth it....just throwing out something for you to think about. If it were my car and I just wanted a fun driver, I wouldn't swap the pistons. If I were building it to kick butt, I wouldn't think twice about shooting for around 11.5:1.
I'm not trying to say it isn't worth it....just throwing out something for you to think about. If it were my car and I just wanted a fun driver, I wouldn't swap the pistons. If I were building it to kick butt, I wouldn't think twice about shooting for around 11.5:1.
..2. As far as the CNC heads/cam car running cam only numbers: There is an unmeasureable difference between one car and it's results and another beyond just cylinder heads. I'd be willing to bet there are MANY heads/cam cars that don't run the numbers that some of the best bolt-on only cars have ran...much less cam only. That is any brand heads/cam cars. Lots of them are 12 second only rides. I have ran better numbers with a 433 bbc with unported cast iron heads (in a bolt on suspension 61 Bel Air than alot of people with aftermarket aluminum headed 496's and 540's in Chevelles, Novas, and Camaros. Combination is everything....
It sounds like you have the heads ported by Pete - CNC Heads, Pinellas Park, FL. In the late 90's/early 2000's, those heads were on some of the fastest B-bodies. Was it the heads, or just the owner doing everything else right? Who knows... All I can tell you is that they won't hold you back.
So true.
It sounds like you have the heads ported by Pete - CNC Heads, Pinellas Park, FL. In the late 90's/early 2000's, those heads were on some of the fastest B-bodies. Was it the heads, or just the owner doing everything else right? Who knows... All I can tell you is that they won't hold you back.
It sounds like you have the heads ported by Pete - CNC Heads, Pinellas Park, FL. In the late 90's/early 2000's, those heads were on some of the fastest B-bodies. Was it the heads, or just the owner doing everything else right? Who knows... All I can tell you is that they won't hold you back.
I hope you don't think I am trying to thread hi-jack you OP. I just wanted to let you know that your heads don't look like my "CNC Heads" branded ones, and to also let you know that just because they may not be one of the most popular brands going doesn't mean they won't be good. I've said it before and I will again....not alot of companies go through the trouble of offering a porting program for LT1's so I doubt they would do so on a port design that sucked.
I found an old picture of my 383 from years ago on my cardomain page to compare your pistons. I had SRP 16cc dish pistons in that engine.
the look identical.
that engine, with stock sized combustion chambers, was about 10.5:1 with the thin mr gasket .026" thick head gaskets.
the engine was a dog. compression may have not been the main problem as there were other problems but it needed to be way higher. as was said earlier the C/R of a N/A LT1 should be around 11.5:1. Id sell the pistons and get flat tops. 5cc relief flat tops on my old 383 would have given me 12:1 with the mr gasket headgaskets, 11.7:1 with fel pro .039" thick head gaskets (if my memory is correct on the felpro gasket thickness).
the look identical.
that engine, with stock sized combustion chambers, was about 10.5:1 with the thin mr gasket .026" thick head gaskets.
the engine was a dog. compression may have not been the main problem as there were other problems but it needed to be way higher. as was said earlier the C/R of a N/A LT1 should be around 11.5:1. Id sell the pistons and get flat tops. 5cc relief flat tops on my old 383 would have given me 12:1 with the mr gasket headgaskets, 11.7:1 with fel pro .039" thick head gaskets (if my memory is correct on the felpro gasket thickness).
While 10.5:1 may not be "optimum" on an all out pump gas LT1, I think you hit the nail on the head with the "other problems". That is stock compression ratio for these....so you could run whatever gas you wanted with your current pistons and no extra expense.
I don't doubt that alot of people push the limits with 12:1 on 93 octane....you'd better have the tune spot on to do so.
I don't doubt that alot of people push the limits with 12:1 on 93 octane....you'd better have the tune spot on to do so.
If the whole topend came from CNC, I bet he's running a small cam. Their setups I've seen have been more street than strip oriented.
HP numbers are interesting when a build is coming together, more than a decade later I think most objective folks want a bit more proof. We all know of engines that make HP but don't run well when actually asked to propel a car rather than a pair of rollers.
Thread Starter
Staging Lane
Joined: Aug 2009
Posts: 75
Likes: 0
From: everett, wa
So what would you experienced guys guys recommend for a fun street car that will occasionnaly see the drag strip/auto x? Given the lower comp pistons and slight oil pressure issues im thinking a freshening up of the motor and new pistons are a good idea or am i just throwing money away?
So what would you experienced guys guys recommend for a fun street car that will occasionnaly see the drag strip/auto x? Given the lower comp pistons and slight oil pressure issues im thinking a freshening up of the motor and new pistons are a good idea or am i just throwing money away?