is 8.48 DCR too much?

[oldgal]

Gents,

I've finally got my 428 running in the 64 Gal but she's got some issues.
 Some background;
The motor is a 69 428 A scratch block with Edelbrock performer RPM heads and performer manifold.  The pistons are TRW 14cc? dish and the cam is a Comp xe262h (inlet valve closes @ 57deg ABDC.)   The only carb I have suitable atm is a 650 DP holley that ran great on the 390.

At first startup she was running real lean and after shut down, 10 minutes, it dieseled till i chocked it with a rag.   found the carb bolts were loose and restarted,  not so lean now but still dieseling after shutdown. 

Went to Wallace racing and used their DCR calculator which says DCR is 8.48:1......  Is this too high or should I chase a larger carb?

PS I'll check DCP in the morning when she's cooled off a bit.  Any help is greatly appreciated...

Cheers,
Phil.

;

[My427stang]

Two parts here, and I hope I come across helpful, sometimes correcting statements comes across wrong

So, first part, I think you are falling into the DCR trap that makes people distrust it.  I actually like it, but it requires a couple of important things.  1 - accurate measurements and 2 - a common tool that has been used on more than one build to have a reference.

Not knowing your exact chamber size (they vary, sometimes wildly) , deck clearance, and what seems to be an assumption on the pistons means that DCR is already unusable.  Second, that Wallace calculator is not one that most everyone uses.  I can't speak for everyone on here, but I can reach out and say most that have experience with comparisons use the PKelly program, which you can download.  The reason using the same one is important is that who knows what the correct number is?  but after 4-5 or 20 builds, if a range using one calculator seems to work, then you can trust THAT calculator for THAT range

So, to the engine.  I did do a WAG DCR just to see then went to the wallace calculator.  Assuming .030 over 14 cc piston, .010 below, 74 cc chamber, .041 gasket with 4.4 bore, and that cam actually with a 57 degree IVC,

PKelley's program says  9.82:1 compression, 8.30 DCR
Wallaces program says lower 8.1 but it's based on static which I had to guess

So you can see that the number is really useless.  Bottom line, I think that combo, is OK, if your numbers are clsoe to the common guesses I just assumed


So, run on.

Here is what I think

1 - Not the carb itself, but possibly adjustment
2 - Timing
3 - Heat
4 - Idle speed

So first, take a good look at your timing.  A good start is 12 initial, but then you need to look at the total to make sure you don't have too much, I'd shoot for 36 total and likely in by 2800.  Good easy rule of thumb

Second, with more initial, you can close the carb, an engine cannot diesel without air, fuel and heat.  Your carb was likely open too far allowing it to get air and some fuel. 

Third, if it's a fresh motor, it'll make some heat for a bit, if there is any way to put fans up, go for a ride, you name it, let it break in.  You can also consider long term putting a colder thermostat in it, but at this point I think it's more carb and timing related.

Fourth, idle it as low as you can.  That little cam should idle nice and low, under 700 IMHO.  As you troubleshoot, if you can't idle it lower, shut it off in gear, but don't let it sit there and chug, that's pretty tough on the reciprocating parts

I'll also ad, better go back and check your work, loose carb bolts...what else is loose? We all make mistakes, I wish I had a dollar for every mess up but once you find something like that, give it a good once over, reset the timing, etc. 

In the end though, I don't think you have a compression problem and you should not need a bigger carb just a properly adjusted one

[oldgal]

Thanks Ross,

The original post was a little rushed, I've now gone and found some real numbers.

The pistons are advertised at 10cc chambers & 10.2:1 SC, the heads are advertised at 72cc, bore size is 4.165,  the rest of your assumptions are spot on.

I think you are correct about the carb being open too far but she stalls below about 1100 rpm(no tach),  I recon the carb idle circuit is working the mixture screws make a tiny amount of difference.  I'll try your suggestion about giving it more initial advance and take it from there.

Thank ya mother for the rabbits!!
Cheers,
Phil.

[My427stang]

Phil

So when doing the calculations, need to consider often that Edels are large as delivered.  Paulie has seen them VERY big, and mine even after cutting slightly were 73cc despite being advertised as 72 before work

The 10cc pistons make sense, but most of the time, they sit low in the block.  Even if they are 1.67 compression height, that puts them 20 thousandths below deck on an uncut FE block.

Also, if using a blue Felpro gasket they can be pretty thick, .050 thick even. 

I wouldn't expect that engine to be over 10:1 unless you purposely machined the deck and heads to get it there

See if you can feed it more initial timing and then readjust idle, hopefully it'll get you there