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

[rumblefish360]

Now that's something I haven't seen a video test comparison done on. I am sure flow out performs compression. But by how much?

That’s a loaded question. It’s actually in answerable. It depends on ever last aspect of every last part of the engine & what size it is.

Steve Dulchich (sp?) wrote about this years back in MoPar muscle magazine. He took a (IIRC) .030 overbored 360 with a zero deck piston in it and ran gasket thicknesses to adjust the ratios.
Then dyno ran them.

Part of the compression ratio is to aid in efficiency by the cams running events lowering dynamic compression as the cam gets bigger.

Head flow testing between stock and various stages of being ported have been done as well.

You can watch engine masters for that. Again our hero if this thread, Steve Dulchich Ported a set of Edelbrock heads to run a comparison to the stock head on a blue print 408 stroker. The cam was a sizable street brawler ilk.

The difference was 92 hp.

 

[rumblefish360]

FWIW: NASCAR tested low compression in the Truck Series years ago. I believe the Ram was running W5 Cylinder Heads.

"Both employ carbureted 358-cubic-inch pushrod V-8s, but in presaging Winston Cup rules, truck compression ratios are limited to 9.5:1, slicing 60 horsepower from Cup cars' 720."

I thought it was only 9.0-1.
Does t matter actually since the cam sizes they run at super speed ways are monstrous and could really wake up from a sweet 13.0-1 or high ratio completely releasing the beast.

 

[ch1ll]

Back in the day, bolting X-heads on a 318 was one of the oldest tricks in the book. Every 318 loved them.

Only to a point, I had/ have one. Hard to tell cause it had 4.55 gears. Ran hard up to 100mph by the 1/8th mile and just stayed there to the stripe, 1/4 mile. Just not enough compression. Still fun till it spun a rod bearing.

 

[318willrun]

Only to a point, I had/ have one. Hard to tell cause it had 4.55 gears. Ran hard up to 100mph by the 1/8th mile and just stayed there to the stripe, 1/4 mile. Just not enough compression. Still fun till it spun a rod bearing.

sounds like too much gear??

 

[ch1ll]

Nope. Not enough compression.

 

[autoxcuda]

Be nice if he did a 30 & 60 overbore flow test also.

That would be interesting too. Like to see the difference between 360 and 340 bores

Would also like to see the difference when the edge of combustion chamber is matched to the bores.

 

[MOPAROFFICIAL]

That would be interesting too. Like to see the difference between 360 and 340 bores

Would also like to see the difference when the edge of combustion chamber is matched to the bores.

That's something I do in all my builds

 

[MOPAROFFICIAL]

Didn't click n watch it. This is widely known stuff. Sounds flawed anyhow.

 

[srduster340]

I've seen, read where some Poly, LA 318's can go to 4.00" bore size and still have adequate cylinder wall thickness. There's a racer, maybe here on this forum with a grey 67-69 Cuda with a 318 block that, according to him, went 4.00". No, I haven't personally done it but I'd check the block to see.

 

[mygasser]

Nope. Not enough compression.

if the revs are maxed out by the 1/8th mile, how much more revs do you think could be achieved by increasing compression to allow the car to keep accelerating all the way to the 1/4? i don't see it myself so i'm curious on your reasoning.
neil.

 

[ch1ll]

if the revs are maxed out by the 1/8th mile, how much more revs do you think could be achieved by increasing compression to allow the car to keep accelerating all the way to the 1/4? i don't see it myself so i'm curious on your reasoning.
neil.

Who said the revs maxed out????????

That's the problem. They didn't cause there was not enough compression, especially with the swap meet cam. Hell, the whole engine was built with swap meet parts. Got 1/2 way through 3rd gear and nosed over.

 

[mygasser]

Who said the revs maxed out????????

That's the problem. They didn't cause there was not enough compression, especially with the swap meet cam. Hell, the whole engine was built with swap meet parts. Got 1/2 way through 3rd gear and nosed over.

so what would you call max revs. putting your 4.55 gear into one of the online speed/rpm/gear calculators and guessing at a 27" tyre (?) at 6000 rpm you're at 106 mph, not far off the 100 mph you quoted at the 1/8. i still don't get the connection with compression if it as you say 'ran hard up to 100 mph'. sounds more like you may have experienced valve bounce and that was what stopped it revving higher (been there, lol.)
neil.

 

[polyjohn]

YEP, you can overbore Poly and LA318 to 4 inches on most early blocks!
Got an LA block at 340 size 4.040 and its fine too.

The 402ci LA and Poly are in fashion as the 340 blocks get harder to find.
360's are more common but the big mains is a power killer...

 

[rumblefish360]

If I can get a 318 to a 4.00 bore, that would work and be great for me.
332.76, I’ll just call it a triple 3 displacement. That OOTB Edelbrock head would work great.

 

[ch1ll]

so what would you call max revs. putting your 4.55 gear into one of the online speed/rpm/gear calculators and guessing at a 27" tyre (?) at 6000 rpm you're at 106 mph, not far off the 100 mph you quoted at the 1/8. i still don't get the connection with compression if it as you say 'ran hard up to 100 mph'. sounds more like you may have experienced valve bounce and that was what stopped it revving higher (been there, lol.)
neil.

What calculator did you use?
30x9x15 goodyear racing slick.
Don't you think it would have valve float in 1st and 2nd gear?

 

[273]

Adding or lowering compression is just gonna raise or lower the entire powerband, not strong on bottom dead on top.

 

[63Dart170]

I loved the old days before the internet when I just threw a set of 340 heads on my 318 and went racing. No one told me I couldn't so I did it, and I went quicker and faster than I did with the 318 heads. Good enough for me.

 

[318willrun]

I loved the old days before the internet when I just threw a set of 340 heads on my 318 and went racing. No one told me I couldn't so I did it, and I went quicker and faster than I did with the 318 heads. Good enough for me.

Always. I miss the days too...

 

[a-bodyguy]

I loved the old days before the internet when I just threw a set of 340 heads on my 318 and went racing. No one told me I couldn't so I did it, and I went quicker and faster than I did with the 318 heads. Good enough for me.

it was right in the mopar bible under 13 sec package
i did it myself

 

[MopaR&D]

People get caught up on "this has a bad effect" but don't consider how it compares to the benefits of the modification, just like with the 340/360 intake on 318 heads. Ok so smaller valves won't be shrouded but then you get way less flow overall with an old set of 273 or 318 heads...

 

[rumblefish360]

The shrouding issue is overrated. Great to avoid if possible.
To many people (here) hang a heavy weight on it like it’s the end of the world.

 

[mygasser]

What calculator did you use?
30x9x15 goodyear racing slick.
Don't you think it would have valve float in 1st and 2nd gear?

this one.... RPM Calculator - RPM to mph
and so with your 30" tyre 98 mph is 5000 rpm so not a lot of revs really.
and yes but it can still 'run hard' up to that point, it just means shifting at an rpm to suit.
i still don't get how more compression will get past too much gear. i've had 2 318's with 340/360 heads and i'm about to build a 3rd (with kb399 domed pistons this time, lol) and both ran easily to 6000 rpm and above with low compression. you said yourself ''Ran hard up to 100mph by the 1/8th mile and just stayed there to the stripe, 1/4 mile''. how is that not too much gear? it sounds like it was set up (gear wise) to run the 1/8 only.
neil.

 

[ch1ll]

It was built with swap meet used parts and the 4.55 gears with the spool was a great deal and in really good shape. So was the cam, Crower hydraulic specs unknown but rowdy as he'll. So were the x heads, 69 stock 340 intake and 650 holley that I had modified to mechanical secondaries. Open used hooker headers. It was my fun car, surprised it launched on that cam with a stock converter, I tried an aftermarket with more stall, but it kept breaking Trans tail pieces, weak front frame rails.

 

[ch1ll]

I tried your calculator and it spit out 117.6 mph. That sounds about what it would trap at.

 

[mygasser]

sounds like the sort of thing i've thrown together in the past using what's 'here' or 'cheap', lol.
sounds a lot of fun, in the 1/8 at least. i just couldn't work out your link to lower compression limiting revs?
neil.