Need your advise Rusty
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Junior User
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From: pa
Need your advise Rusty
Thank you for answering my questions on cylinder.Here's what I want to do,I Have a remanufactured 390 mirror 105 block I Would have to guess its punched out 30 over, the valves are hanging up in the D2TE-AA heads I've heard its a common problem with Autotech rebuilds.So I want to get the C4's redone along with Edelbrock Performer RPM intake, 600 Holley, Hedman headers, also Mr Gasket 0.20 Mag-1132 gaskets Mr Gasket 1 inch 4 hole phenolic spacer.Its an everyday driver. I've been reading all the posts about cylinder heads and you are certainly are a wealth of info. I would greatly appreciate any advise. Thankyou, Craig.
Post Fiend
Joined: Jan 2003
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From: Iowa
It should work good. I would advise you have all new valve guides and all new valves put in those heads. Be sure to get the valves first so the machinist can exactly match the new guides to the valve stem diameter. I've seen valve stems on new replacement valves .003" under what a stock valve is! I would also advise that hardened exhaust valve seats be put in the heads.
While you have the heads off, take a look at the pistons to see if they have a dish or not, and measure piston to deck clearance. Not really a critical thing to do, but it lets you accurately compute the compression ratio. Also, if the piston is closer to the deck than .010" you'll need to use thicker head gaskets.
I'm not a big fan of carb spacers, so whatever floats your boat there.
While you have the heads off, take a look at the pistons to see if they have a dish or not, and measure piston to deck clearance. Not really a critical thing to do, but it lets you accurately compute the compression ratio. Also, if the piston is closer to the deck than .010" you'll need to use thicker head gaskets.
I'm not a big fan of carb spacers, so whatever floats your boat there.
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From: pa
RustyI'm not a big fan of carb spacers too, but I may need the carb heighth so the throttle linkage clears, and what about all the talk about an insulator to keep the carb cool? Rusty if you could please explaine, I'm sorry but I don't know how to check for pistons with a dish, and the piston to deck clearance. Is that the distance from tdc of the highest point of that piston to the deck of the block? Thank you, you've already been a big help. Craig
Posting Guru
Joined: Aug 2005
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From: NE Ga
just out of curiousity guys, why are you not a big fan of spacers? I bought a 2" phenolic 4v for my 390 but haven't opened it yet b/c i wanna make sure the clearance is there. I don't know that much about them except the fact that it keeps my carb cool and supposedly more low end torque . I purchased the one with the spiral cut vortex. Any cons i should be aware of?
Posting Guru
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From: the side of a mountain
http://store.summitracing.com/largei...UEM-KB150030-8 that is a dished piston. it has some of the top machined out to lower compression ratio. a flat top piston is one like in rustys avatar, and a dome piston is the oppisite of a dish raised to increase compression. most likely they will be flat top or dish. you are right on measureing deck clearance, piston at tdc and from the highest point to the deck of the block.
Post Fiend
Joined: Jan 2003
Posts: 8,600
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From: Iowa
It's my opinion that carb spacers do more to screw up airflow than you gain. If you are having problems with the carburetor boiling the gas, then you might consider a thick foam insulating gasket. Also, when I was running a carburetor spacer, I ran into icing problems on damp mornings when the temperature was near freezing.
When looking at a typical example of a piston dish, those KB150 pistons aren't really the thing to look at. They have an interesting design with an offset dish. For a more typical look at a dished piston, look at this:
A flat top with 4 valve reliefs looks like this:
To measure piston to deck clearance, you bring the piston to TDC. Then, you can either use a dial indicator, or you can do it like I do it, and use a ruler and a set of feeler gauges. You are measuring how far the top of the piston is down in the cylinder when it is at top dead center. This is a critical measurement in any motor, so it is nice to know if you're going to be in there anyway.
When looking at a typical example of a piston dish, those KB150 pistons aren't really the thing to look at. They have an interesting design with an offset dish. For a more typical look at a dished piston, look at this:
A flat top with 4 valve reliefs looks like this:
To measure piston to deck clearance, you bring the piston to TDC. Then, you can either use a dial indicator, or you can do it like I do it, and use a ruler and a set of feeler gauges. You are measuring how far the top of the piston is down in the cylinder when it is at top dead center. This is a critical measurement in any motor, so it is nice to know if you're going to be in there anyway.
Postmaster
Joined: Jul 2003
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From: iowa
i'm a nobody but i will throw my opinion out there on carb spacers. They are bs for the most part. I have seen several dyno results where the engines lost hp or and torque with different carb spacers. The open style ones are the biggest gamble.
Imho the only thing a carb spacer does is add plenum volume, and that is useful on the topend. They talk about spacers improving signal draw, and helping lowend power is questionable.
imo if you are going to or have to run one, i'd go with a 4 hole spacer. A 2bbl is in more need of an spacer than anything.
And if you think i am biased look in my gallery under the carb!
Imho the only thing a carb spacer does is add plenum volume, and that is useful on the topend. They talk about spacers improving signal draw, and helping lowend power is questionable.
imo if you are going to or have to run one, i'd go with a 4 hole spacer. A 2bbl is in more need of an spacer than anything.
And if you think i am biased look in my gallery under the carb!
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