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Budget 385sbc upgrades...too much compression?

General engine tech -- Drag Racing to Circle Track

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travis
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Budget 385sbc upgrades...too much compression?

Post by travis »

4.040x3.75” sbc, hypereutectic 2vr flat tops w/5cc valve reliefs, .010” deck clearance, 4.166x.041” head gaskets.

Old combo had 76cc SR Torquer heads for about 9.5 compression and a 222@.050 Crane single pattern HFT cam, performer 2101 intake and a 750 Edelbrock carb. Ran fine on 91 octane.

New parts...Vortec heads with polished chambers and a sanding roll cleanup of the ports. Measured 64cc chambers, stock 1.94/1.50 valves, comp 26915 springs, screw in studs. Crower 00321 solid flat tappet, 274/282 advertised, 242/248@.050, 114 lsa/110 ica, .482/.504” lift. 1.5 roller rockers, performer 2116 or rpm 7116 if it will fit under the stock hood.

Car is a guesstimated 3600 pounds w/driver, TH350 with a 2800-ish 10” converter, 3.42 gears. 255/60-15 street tires. Street performance build that gets driven a lot.

Compression with the new heads is going to end up around 10.8-1. Do y’all think this will be ok on 91-93 octane pump fuel? Or should he consider a different set of heads?
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Re: Budget 385sbc upgrades...too much compression?

Post by turbo camino »

110 LSA and a 3500-3800 converter will help it not knock the ring lands out. 114 LSA plus a tight converter plus iron heads is too many strikes against it, IMO.
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Re: Budget 385sbc upgrades...too much compression?

Post by PackardV8 »

Just askin'; why the choice of a 114 LSA cam?
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Re: Budget 385sbc upgrades...too much compression?

Post by 1980RS »

With a 114° LCA you will be fine with pump gas and don't run more that 31 degrees total timing with the Vortec's that where they make the best power. If your cam was a 106° LCA than you might have some problems.
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Re: Budget 385sbc upgrades...too much compression?

Post by bigmike »

Compression with the new heads is going to end up around 10.8-1. Do y’all think this will be ok on 91-93 octane pump fuel?
I can tell you a couple years ago a guy that I know tried to run a SBC 383 flat top with 64 cc heads in a 1/2 ton pickup with 3.73 gears on 91 octane. It failed miserably only lasted about 300 miles. Two pistons had broken ring lands all the cylinder walls had scuffing and or scoring, same with the pistons and skirts.

I'am not much of a fan of 114 LCA cams on SBC. What made you go that route?
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Re: Budget 385sbc upgrades...too much compression?

Post by turbo camino »

Can we please use LSA and ICL? 'LCA' is not an actual thing.
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Re: Budget 385sbc upgrades...too much compression?

Post by steve cowan »

travis wrote: Fri Oct 16, 2020 8:47 pm 4.040x3.75” sbc, hypereutectic 2vr flat tops w/5cc valve reliefs, .010” deck clearance, 4.166x.041” head gaskets.

Old combo had 76cc SR Torquer heads for about 9.5 compression and a 222@.050 Crane single pattern HFT cam, performer 2101 intake and a 750 Edelbrock carb. Ran fine on 91 octane.

New parts...Vortec heads with polished chambers and a sanding roll cleanup of the ports. Measured 64cc chambers, stock 1.94/1.50 valves, comp 26915 springs, screw in studs. Crower 00321 solid flat tappet, 274/282 advertised, 242/248@.050, 114 lsa/110 ica, .482/.504” lift. 1.5 roller rockers, performer 2116 or rpm 7116 if it will fit under the stock hood.

Car is a guesstimated 3600 pounds w/driver, TH350 with a 2800-ish 10” converter, 3.42 gears. 255/60-15 street tires. Street performance build that gets driven a lot.

Compression with the new heads is going to end up around 10.8-1. Do y’all think this will be ok on 91-93 octane pump fuel? Or should he consider a different set of heads?
If you have tune up close and coolant temps under control i think you will be fine.
I have run similar compression with aggressive comp oval track SFT cams with 1.6 rockers and tight LSA (106) in my streeter at 3650 pounds with over 70 passes per year and plenty of street driving.
On engine disassemble everything looked fine,I always kept ignition timing no more than 32 deg and coolant around 180 if possible.
My opinion is most engine failures are tune related.
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Re: Budget 385sbc upgrades...too much compression?

Post by travis »

So here is the way I understand it...

This guy had this 385 built a couple years ago. He thought it had the 67cc SR Torquer heads and 12cc dished pistons, plus this 278 Energizer cam. He loved the engine...loads of bottom end tire frying torque but it was done by 5200 rpms. His corvette buddies talked him in to this combo (Vortecs and the 00321 cam) with the assumed dished pistons...it was supposedly the holy grail of a pump gas street 383 with plenty of vacuum and yet plenty of RPM’s. When I pulled the heads off today, all these assumptions was found to be incorrect lol. I had no input on anything...I was just supposed to be the manual labor.

This was supposed to be a quick weekend job, cash money up front deal, with the full understanding that I am not responsible for how it runs, just that everything is installed and set up correctly. Now...I’ve got the engine out of the car and torn apart, and I’m honestly not comfortable putting this thing together. Hyper pistons with this much compression makes me a bit nervous.

The only cam I have on hand that would “work” is a crane reproduction -140 cam, but I think it would be a turd in this engine especially with the 3.42 gears and current converter.

The guy is supposed to call me back in the morning with a decision on how he wants to proceed...
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Re: Budget 385sbc upgrades...too much compression?

Post by travis »

steve cowan wrote: Sat Oct 17, 2020 12:46 am
If you have tune up close and coolant temps under control i think you will be fine.
I have run similar compression with aggressive comp oval track SFT cams with 1.6 rockers and tight LSA (106) in my streeter at 3650 pounds with over 70 passes per year and plenty of street driving.
On engine disassemble everything looked fine,I always kept ignition timing no more than 32 deg and coolant around 180 if possible.
My opinion is most engine failures are tune related.
The car has a big aluminum radiator and dual electric fans. He swears it has always run 170-180 degrees even in the heat of summer.
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Re: Budget 385sbc upgrades...too much compression?

Post by steve cowan »

travis wrote: Sat Oct 17, 2020 12:47 am So here is the way I understand it...

This guy had this 385 built a couple years ago. He thought it had the 67cc SR Torquer heads and 12cc dished pistons, plus this 278 Energizer cam. He loved the engine...loads of bottom end tire frying torque but it was done by 5200 rpms. His corvette buddies talked him in to this combo (Vortecs and the 00321 cam) with the assumed dished pistons...it was supposedly the holy grail of a pump gas street 383 with plenty of vacuum and yet plenty of RPM’s. When I pulled the heads off today, all these assumptions was found to be incorrect lol. I had no input on anything...I was just supposed to be the manual labor.

This was supposed to be a quick weekend job, cash money up front deal, with the full understanding that I am not responsible for how it runs, just that everything is installed and set up correctly. Now...I’ve got the engine out of the car and torn apart, and I’m honestly not comfortable putting this thing together. Hyper pistons with this much compression makes me a bit nervous.

The only cam I have on hand that would “work” is a crane reproduction -140 cam, but I think it would be a turd in this engine especially with the 3.42 gears and current converter.

The guy is supposed to call me back in the morning with a decision on how he wants to proceed...
I think your concern is certainly justified,
I stopped doing private work a couple of years ago because some people won't listen sometimes ,and my own time was worth more,seem to spend more time talking to people who can't decide which way to go or want to save money,so now I don't bother.i am happy to wreck my own stuff in the name of testing but not other peoples stuff.
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Re: Budget 385sbc upgrades...too much compression?

Post by F-BIRD'88 »

I'd verify that it will is in fact a 383. check crank.
May be just a flat top 350. Why not full port the S/R heads?
Use comp XS274S-10. The RPM intake will fit on the vettes that have the fresh air lil cowl hood of f the right air cleaner is used. . Keep the cr UNDER 10.5:1.
91 and 93 Octane are are very different.

If using the vortecs use the correct 12cc D dish pistons.
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Re: Budget 385sbc upgrades...too much compression?

Post by mt-engines »

F-BIRD'88 wrote: Sat Oct 17, 2020 11:37 am I'd verify that it will is in fact a 383. check crank.
May be just a flat top 350. Why not full port the S/R heads?
Use comp XS274S-10. The RPM intake will fit on the vettes that have the fresh air lil cowl hood of f the right air cleaner is used. . Keep the cr UNDER 10.5:1.
91 and 93 Octane are are very different.

If using the vortecs use the correct 12cc D dish pistons.
why keep the compression under 10.5? i ran 11:1 with just a comp xe274h10 shredded tires got decent fuel economy and was snappy as hell. never had a problem 92 pump. just dont go stupid with ignition timing
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Re: Budget 385sbc upgrades...too much compression?

Post by levisnteeshirt »

Local altitude ,, 114LSA cams usually make a sbc lazy as hell
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Re: Budget 385sbc upgrades...too much compression?

Post by travis »

The owner made the decision to use what he had, so after a 14 hour thrash yesterday, then a couple more hours this morning to double check valve lash and give everything a once over, it is done.

With 18* in the distributor, 12 initial and a conservative timing curve (full advance in at 3600), there was no detonation that I could see on the plugs or hear. It isn’t super snappy, but it isn’t bad either. Surprisingly mild idle with 16.5-17” vacuum. It pulls smoothly from about 2200 rpms to 6000 (I didn’t push it any harder), and the valvetrain was very quiet.

The owner didn’t seem too thrilled with how mild mannered it is, so there may be more parts swapping in the future
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Re: Budget 385sbc upgrades...too much compression?

Post by PRH »

A 114lsa will really mellow out a cam in that size range.

I had a 383 Mopar on the dyno some time back, 9.7:1, bowl ported stock heads, rpm intake, tight lash .875 lobe cam, 243/247-114, ran it with ex manifolds.
The idle was basically smooth....... almost no lope at all.

I didn’t have it sprung quite heavy enough....... it started to show signs of valvetrain instability @6500....... and the power was still going up at that point, although just slightly.
Somewhat handy with a die grinder.
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