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Forged Aluminum Pistons vs. Cast Alum

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#21 ·
Re: Forged Aluminum Pistons vs. Cast Iron

I'm running 54's in my 4bbl and she's rich. I would go 52 or even a notch less.

That's on my to-do list. We have close to the same set up.

All my engine problems were due to my cam. Turns out I'm not nearly as bad at tuning a carb as I thought I was....

Get a vacuum gauge to set the idle air mix. Can't emphasize that enough.

...it certainly seems like we're building the same engine but I'm about 2 months ahead of you...


Vacuum leak: I think you still have one. Try pinching the hoses or plugging them entirely until you track it down. The backfiring is caused by a lean condition most likely. In my case it was the down at the trans. There's a hard vac line that runs from near the car down to the tail shaft, has a 2" long rubber hose and then goes into the trans there. Mine was missing that rubber hose. Took forever to find!

If it's not the cam it could be valve seats. Since you're getting the head done anyway that'll be fixed.


Some eye and ear candy for you: https://www.youtube.com/watch?v=Xeib6eoMn8c&feature=youtu.be

(that puff of smoke is because the squirter was too big. Backed down and it went away... Too much gas at full throttle. Plugs were dripping!)

Notice how the engine doesn't shake at all and has quick response? That's after the cam swap. Before that the whole car would shake because the #6 exhaust valve was barely opening. It was OK at higher RPM's but horrible at idle. Lot of people said it was a vacuum leak.

PS: I can now spin my tires!
 
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Discussion starter · #22 ·
Re: Forged Aluminum Pistons vs. Cast Iron

Hey Gbauer,

Yes, your build has given me confidence that these sixes can run well! I've been following your build closely to see how it turns out. As you say, we're very close to the same engine with some differences. Here's the summary:

  • holley 4BBL 390CFM, offy intake (same)
  • Langdon split headers into 2.5" pipe to single muffler with dual 2.25" outlets (almost same)
  • .489 lift comp cam (same)
  • 307 flat top pistons going in (you're thinking about it, but if it runs great...)
  • porting the head, but not lumps. you're getting great performance with a stock head, larger valves will get me most of the way. the thing that tipped me over (outside your engine coming out great) was that it's local. no shipping, I can run up to the machine shop if there are issues. another guy just rebuilt another Camaro just like this. not quite out of the shop yet, but it'll be ready. another friend has a stock '68 Camaro with 250, holley 4BBL and has great luck with it. He can spin tires. :)
  • looking at putting in A/C. it seems that it would be easier with the engine out, but that's a lot of things to change in a short period of time. I'll go look on the other forum for info.
  • just bought a 200R4 transmission which will go in with the new engine. My budget's about blown so I won't be changing the gearing in the rear end this year.

Back to the backfire through the intake. I plugged all the vacuum lines one at a time but no effect. when I tuned the idle speed mixture with a vacuum gauge, it didn't seem to work probably 'cause my jets are too big. Thanks, I'll order a few sizes of jets, but try the size you recommend first.

Getting excited, engine goes in Friday morning. My bday gift to myself! gobble, gobble. :)

Mark
 
Discussion starter · #23 ·
Re: Forged Aluminum Pistons vs. Cast Iron

mshaw67 said:
  • looking at putting in A/C. it seems that it would be easier with the engine out, but that's a lot of things to change in a short period of time. I'll go look on the other forum for info.
Click to expand...
I downloaded the directions to installing A/C. Not gonna happen this year, too much work for the precious little time I have to spend. Engine and transmission are plenty for this winter. I'll just replace the heater core and stick with 4 x 60 A/C. I'll be happy to have the car back on the road in Feb (Jan if it goes magically well).

Mark
 
#24 ·
Re: Forged Aluminum Pistons vs. Cast Iron

mshaw67 said:
Hey

Back to the backfire through the intake. I plugged all the vacuum lines one at a time but no effect. when I tuned the idle speed mixture with a vacuum gauge, it didn't seem to work probably 'cause my jets are too big. Thanks, I'll order a few sizes of jets, but try the size you recommend first.

Mark
Click to expand...
Jet size has nothing to do with idle circuit. Look at timing and adjust idle screws
 
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#25 ·
Re: Forged Aluminum Pistons vs. Cast Iron

mshaw67 said:
I downloaded the directions to installing A/C. Not gonna happen this year, too much work for the precious little time I have to spend. Engine and transmission are plenty for this winter. I'll just replace the heater core and stick with 4 x 60 A/C. I'll be happy to have the car back on the road in Feb (Jan if it goes magically well).

Mark
Click to expand...
Honestly after putting in 50 sq feet of GTMat (Dynamat knock off) I've found I rarely need AC. It lowered the temps by a good 10-20 degrees inside the car.

http://www.ebay.com/itm/like/110920...AhuR8P8HAQ%26srcrot%3D711-117182-37290-0%26rvr_id%3D937550361954&chn=ps&lpid=82

Easily fits in your time constraints.
 
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#26 ·
Re: Forged Aluminum Pistons vs. Cast Iron

Vega$69 said:
Jet size has nothing to do with idle circuit. Look at timing and adjust idle screws
Click to expand...
Single idle screw. Dual idle air screws.

Might be leaks at the intake/ head flanges.

The only way to tell is to take carb cleaner and start spraying until you find it.

Also might be the float.

Honestly I'd start from.scratch and work my way through the whole carb/timing/etc.
 
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Discussion starter · #27 ·
Re: Forged Aluminum Pistons vs. Cast Iron

Took the engine in today. Mechanic thought the cylinder with the light colored exhaust valve was running okay, but said the color should be a bit darker.

He didn't like the hash marks in the cylinder. Made lots of grumbling comments about people who don't have the right equipment or use the wrong stones (or something of the like). He thought the hashes were too deep, as I believe somebody has mentioned. It's a good chance it'll get bored out to 040 to ensure a nice round hole with a good, appropriate finish.

Thanks again for the advice,
Mark
 
Discussion starter · #28 ·
Re: Forged Aluminum Pistons vs. Cast Iron

What we have are similar symptoms with the original carb/intake and new holley carb/offy intake. Backfiring (that's getting worse over time) and awful performance, although Holley was better than stock. I verified every vacuum line was good, vacuum readings at idle were decent and pretty smooth. I replaced the intake manifold gasket and used RTV to ensure there wasn't a leak there.

I continue to suspect multiple problems. But this week I was looking closely at my carb setup that has a 1" spacer to prevent obstructions. There's a danged logo/numbering on the spacer which I'd put facing up towards the carb. The carb has some passages between barrels that give more opportunity for vacuum leaks.

On one of the last runs before I tore the engine out, I took carb cleaner to the car. I sprayed all over the place, couldn't find anything. But there was an area when I really doused the primary side of the carb would cause the RPMs to drop. Hmmmm, but I couldn't even see where it was. I thought since the cleaner was dripping on everything maybe some made its way in through the throttle shaft.

Looking at the pictures, it looks like you and those at inliners.org called it. A vacuum leak.

Below is the carb and the spacer, the spacer is flipped up. You can see on the spacer how the seal isn't made where the passages are discoloration. Look closely at how little metal is there to make the seal with the gasket.

Image


Now look at the primary side of the gasket (rotated clockwise). A bunch of photoshop to try to better highlight the dark streak that blasts right through the "CAT NO. 6006" and on out. Next to it is some weird texture, like it soaked up something (maybe my carb cleaner?). It looks much too much like coincidence.

Image


I'm changing up the carb when the engine comes back together, will either flip the spacer or hopefully chunk it.

Thanks!
Mark
 
Discussion starter · #29 ·
Re: Forged Aluminum Pistons vs. Cast Iron

Brief chat with the machine shop today. Shocking results!

1. Valve springs are weak, 10-15 lbs lighter than spec. This is likely cause for some of the backfires and a reason why it happened on both carbs. The other leak certainly contributed.

2. "It's about the worst bore and hone job I've ever seen." He thought the hash on that would chew right through new rings. Pistons will be bored out to 0.040 (0.030) today.

3. The wrong pistons were installed at the last overhaul! When I brought the engine in, Bill kept looking funny at the engine. He got out his measuring device, but didn't say much. I thought maybe it wasn't TDC, but it actually was. Turns out that 250 CID pistons were installed with the shorter-stroke 230 CID engine. Rough estimate that the compression ratio was somewhere around 6:1 at best and the cause of my 105-110 PSI compression. This makes me feel good that there was a major defect that was causing this engine to run so horribly and that when it's done with the 250 crankshaft, flat-top pistons and moderate CAM, that this engine is going to SING! I didn't have a good picture at TDC, but did find one. Jim pointed out that ordering the wrong pistons can be forgivable since somebody assumed it was a 250. But how does one put the engine together and not notice? Oh yeah, that's right, considering the boring job, it may have been done in somebody's garage.

Anybody experience this sort of error before?

Image
 
#30 ·
Re: Forged Aluminum Pistons vs. Cast Iron

Getting the right pistons in there is going to be a dramatic improvement!
Also, i bet the 200-4r trans gearing makes the car feel about 800 pounds lighter. This is going to be good! I think youll be able to beat that 0-60 of 20 secs pretty easily.:D

Are you having the engine balanced?
 
#31 ·
Re: Forged Aluminum Pistons vs. Cast Iron

I assume you're talking about the cross hatch pattern honed on the cylinder walls.

I could see the wrong pistons ordered but to actually install them and button it up with them .25 in the hole show the builder was clueless.
 
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Discussion starter · #32 ·
He's going to match the rod weights and use a very nice machine to balance the crankshaft. It spins the crank and puts directions on the computer screen about where and hw much material to remove. Is that what you mean by balancing?

Yes, by bore and hone, i mean the cross hatch pattern. I've only seen closely a handful of engines ater bore/grind, but this one looked vey different. Especially for over 3000 miles. The grooves are really deep, golden in color perhaps oil staining they were so deep.

This car will rock when done! Trying to be realistic, startup will be as late as February with all these changes. There's always a bracket to modify. :)

Oh, a question i haven?t asked the machnist yet. Should I expect to have seats installed on the exhaust valves? I'm putting in larger intake valves, but keeping exhaust same size. Some porting leanup, but not lumps.

Thanks!
Mark
 
#33 ·
Re: Forged Aluminum Pistons vs. Cast Iron

If you don't have them already you need hardened seats due to now using unleaded fuel.
 
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#34 ·
Re: Forged Aluminum Pistons vs. Cast Iron

I forget if you have a SBC or a BBC. But the latest improvements in BBC heads have shown that even the newer cast aluminum raise port aftermarket heads still suffer from a poor exhaust port. As such a split duration cam and a larger exhaust valve helped more than going for the largest available intake valve. This is just about required on a standard location exhaust port head.

With factory cast iron oval port open chambered heads I would recommend new sil-bronze 11/32nd of an inch valve guides, hardened exhaust valve seats and a choice of 2.30" and 1.90 inch swirl polished stainless steel valves. The cost of these parts and machine work labor costs will about equal the cost of a set of aftermarket aluminum heads. You will however make about two percent more power with the cast iron over identical aluminum heads but that won't be enough to compensate for the faster elapsed time offered by the aluminum heads weight savings.

Best factory head made is the Signature Series oval port head found on the ZZ502 (GM part number12363390). It is based upon an Edelbrock RPM series BBC open chamber head that has even larger valves and was then CNC pocket ported and gasket matched to the intake (port is actually ROVAL in shape, or a reduced height rectangular port head sized for a 454 or a 502 motor). Under 500 cubes you want to avoid a rectangular port head as they have a very inefficient port design, unless of course you are not running a set of 4.88 or 4.56 rear gears to keep the RPM up high enough to use the larger intake port size.

If you have a SBC ignore this as I spend far too much time on line answering posts and some times forget what the original question was.

Big Dave
 
#36 ·
Re: Forged Aluminum Pistons vs. Cast Iron

LOL!!!l:)
 
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Discussion starter · #39 ·
Re: Forged Aluminum Pistons vs. Cast Iron

Stopped by the shop today. The head is mostly done already. New valve guides added, hardened exhaust seats (valves remain 1.5"), intakes increased from 0.172 to 0.184.

He'll do a some porting and smoothing out the chambers. There was originally pollution smog pump on this with a big air-tube rod running right through the middle of each exhaust port. All gone now...

No SBC or BBC yet, don't even know what they are. Always interesting to read about what the big boys are up to! :)

Image
 
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