BORE SHROUDING TEST: 4.03" vs 3.91" Edelbrock RPM Heads Really Fit a 318? Project Mission Impossible

[66fs]

You guys need to just build stuff. Dyno's and theoretical stuff can or can not help. A guy I know was racing dirt track with a 318 and 340 X heads, had the fastest car on the track. That test is questionable at best. My experience is the same as 318willrun, 340/360 heads with any either 1.88 or 2.02 intake valves takes a 318 to the 340 level. I always had the heads milled .040 and .038 intake side to keep the compression the same or better. Of course you also need the cam, valve springs, intake, carb, and distributor.

 

[rumblefish360]

You guys need to just build stuff. Dyno's and theoretical stuff can or can not help.

You hit the nail on the head right there buddy. Just build something. Get out and do it. Throw some caution to the wind.
Pre internet and before I knew of the MP books, and after as well, if you wanted to know something, you built it and tried it. Dyno time was way to expensive but the track was fun, cheap by compare and has an accurate timing system to track your results.

I had so many carbs, intakes, camshafts, cylinder heads, 8-3/4 gear sets, it was stupid. Still do today to a lesser degree.

That test is questionable at best. My experience is the same as 318willrun,

I wasn’t to keen on the tape used to reduce the bore size, but, it did seem to work. Having an entire sleeve for a closer to actual real life scenario would have been perfect. Sounds pricey to me to do.

The real honest key here is where and how the fuel flows past the valve into the cylinder.

I also echo the 318WR actions and results. It’s amazing how the 318 gets the hard hitting disrespect hammer so often. I do prefer to build one in the future with as much over bore as I can get out of it but it’s not the end of the world if I don’t. I would just prefer it.

I’m looking forward to this 318 experiment.

 

[66fs]

... I also echo the 318WR actions and results. It’s amazing how the 318 gets the hard hitting disrespect hammer so often. I do prefer to build one in the future with as much over bore as I can get out of it but it’s not the end of the world if I don’t. I would just prefer it...

I prefer the smallest bore to keep the cylinder walls as thick as possible. Maybe grind a notch and radius the area of the intake valve (staying out of the ring travel). But to tell the truth, I've run 1.88 intake "J" heads on a 273 with a 3.665 bore. Guess what? It ran like a 340, no notches or special tricks except centering the chambers on the bores. The most important thing to making power with a short block is to seal the bores at wide open throttle, WOT.

 

[rumblefish360]

I prefer the smallest bore to keep the cylinder walls as thick as possible. Maybe grind a notch and radius the area of the intake valve (staying out of the ring travel). But to tell the truth, I've run 1.88 intake "J" heads on a 273 with a 3.665 bore. Guess what? It ran like a 340, no notches or special tricks except centering the chambers on the bores. The most important thing to making power with a short block is to seal the bores at wide open throttle, WOT.

While I agree a thicker cylinder wall is better, over boring an engine, it’s not something I shy away from depending on the sonic check report.

I have had 340 blocks that are thin at a .020 overbore. They still work and run fine. Just a darn shame they were thin walled to begin with.

The valve shrouding is something to avoid though everyone gets out of control when there is some. It’s great to avoid but over rated in its effects. As soon as it’s seen or heard about, the nay sayers dog pile on top like your the stupidest man to walk the earth.

Attention has to be paid to the air flow down the port, past the valve into the cylinder. When you know how that path is traveled, porting can help, not solve the issue.

As you said and we have experienced, more power is made even with valve shrouding occurring. It’s still more airflow in.

Improving the air/fuel quality is the area to look at. Redirecting the A/F path a little bit helps in big ways. Only so much can be done. After that, I just simply ignore it.

 

[273]

You guys need to just build stuff. Dyno's and theoretical stuff can or can not help. A guy I know was racing dirt track with a 318 and 340 X heads, had the fastest car on the track. That test is questionable at best. My experience is the same as 318willrun, 340/360 heads with any either 1.88 or 2.02 intake valves takes a 318 to the 340 level. I always had the heads milled .040 and .038 intake side to keep the compression the same or better. Of course you also need the cam, valve springs, intake, carb, and distributor.

All it is, is a piece of information, outside of the 15-25 cfm loss across most the lift range it tells us little in itself, how an engine will respond from this loss ? To me 400 hp and under probably very little looking at how sub 400 hp 318 perform. But at some point it probably does have an effect. But since most aren't building 500/600+ hp 318 most will probably never be overly effected.

 

[273]

This topic reminded me of this build, the ported EQ results I all ways found a little disappointing.

The shrouding might be/part the cause of this 400 hp 318 recipe, when they upgraded the 1.92 EQ's (402 hp) to ported 2.03 EQ's (227 VS 273 cfm @ .500" lift) and got 425 hp both at 6,200 rpm.

For a gain of 45 cfm the 23 hp gain is a little disappointing, might of been better porting but keeping the 1.92 valve.



Chrysler 318 Engine - A Powerplant To Brag About

LIFT:	INT:	EXH:	INT:	EXH:
. 100	68	57	69	60
. 200	124	114	138	124
. 300	179	155	200	169
.400	213
.500	227
.600	233

 

[360notch]

Depends on exactly how much cr vs how much overall airflow gain (VE%), Airflow generally has way more potential.

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