COMPRESSION, Pistons WITH VORTEC HEADS

hogg

Veteran Member
Dec 29, 2000
3,200
pegram,tn.,cheatam
I have a 400 SBC just put in machine shop . Going to need new pistons, .030 over, what will be a cheap , decent, dish piston ,for a street motor,never see over 5500 rpm with Vortec heads , Got a set of used flat tops but afraid to use them because compression be to high, i think, with the vortec i would like to use. like to have some input.
 

G72Zed

Veteran Member
Sep 8, 2015
4,072
Canada
Well, assuming the typical composition HG and zero deck block, the typical FT piston with 2 valve reliefs with about 5 cc would put you at 11:7 CR or so if those Vortec's are in the 64cc range.

Getting to 96cc at TDC, you would need a 23 cc reverse/inverted dome to hit a more friendly 9:7 CR with those assumed 64cc Vortec's.

Again, only way to be certain is to measure things up.

Mahle Power Pak make some nice piston kit's, so does JE/SRP and a few others. Most are 4032 forged, not sure about the Hyper options out there...I'm not fussy on those.
 
Apr 23, 2015
39
san diego california
I´m running ROSS flat tops, with Vortecs on a 400 sbc and have no detonation issues, maybe the cam choice helped me avoid detonation, running an Edelbrock Performer RPM flat tappet(234 int 238 exh adv duration), engine was balanced by Crower and i´ve taken it to 7,000 rpm once or twice, but it definetly runs out of steam by 5,000-5,200 rpm, it makes mountains of torque and it'll spin the tires in third gear, was running a Saginaw 4 speed and a 3.42 rear, got to dial in ignition timing, no more than 34 deg total advance, 165 deg thermostat and dual electric fans. btw I crudely measured my heads, and they came out at 66cc.
 

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1980RS

Veteran Member
Jun 17, 2006
6,380
MN
My Vortec 406 that I opened the chambers up to 68cc's with a flat top piston and .039 gasket was right at 10.8 to , much like Thunders engine I ran an Elgin Hyd cam with my ported super Victor and it powered my Camaro into the high 10's. I even tan a dished 400 with a set of 906 Vortec's, 286H cam with an RPM intake. That engine was in the 12.20's and was so drivable I would put it in truck to pull my trailer if needed. With my flat top 406 I ran 100 oct fuel but the good thing with Vortec heads is they only need 32° timing to make great power.
 

sandlapper

Veteran Member
Oct 9, 2020
1,465
SE CSA
Well, assuming the typical composition HG and zero deck block, the typical FT piston with 2 valve reliefs with about 5 cc would put you at 11:7 CR or so if those Vortec's are in the 64cc range.

Getting to 96cc at TDC, you would need a 23 cc reverse/inverted dome to hit a more friendly 9:7 CR with those assumed 64cc Vortec's.

Again, only way to be certain is to measure things up.

Mahle Power Pak make some nice piston kit's, so does JE/SRP and a few others. Most are 4032 forged, not sure about the Hyper options out there...I'm not fussy on those.
this x2

I'd also spring for 6" rods and reverse/inverted pistons w/ appropriate compression height.
 

G72Zed

Veteran Member
Sep 8, 2015
4,072
Canada
I´m running ROSS flat tops, with Vortecs on a 400 sbc and have no detonation issues, maybe the cam choice helped me avoid detonation, running an Edelbrock Performer RPM flat tappet(234 int 238 exh adv duration), engine was balanced by Crower and i´ve taken it to 7,000 rpm once or twice, but it definetly runs out of steam by 5,000-5,200 rpm, it makes mountains of torque and it'll spin the tires in third gear, was running a Saginaw 4 speed and a 3.42 rear, got to dial in ignition timing, no more than 34 deg total advance, 165 deg thermostat and dual electric fans. btw I crudely measured my heads, and they came out at 66cc.

If timing and the tune is on, it's surprising what you can get away with as far as SCR with well "shaped" cylinder heads and the right cam.....

I was on the dyno tuning a mild 383 that was 11:4 with Iron 305 Vortec's on pump fuel, it was a little monster LOL.
 
Apr 23, 2015
39
san diego california
My Vortec 406 that I opened the chambers up to 68cc's with a flat top piston and .039 gasket was right at 10.8 to , much like Thunders engine I ran an Elgin Hyd cam with my ported super Victor and it powered my Camaro into the high 10's. I even tan a dished 400 with a set of 906 Vortec's, 286H cam with an RPM intake. That engine was in the 12.20's and was so drivable I would put it in truck to pull my trailer if needed. With my flat top 406 I ran 100 oct fuel but the good thing with Vortec heads is they only need 32° timing to make great power.
How high you har to rev your engine to get to high 10s? my vortecs are not ported.
 

sandlapper

Veteran Member
Oct 9, 2020
1,465
SE CSA
If you have vortec chambers (or similar), and you need a dish--- if at all possible, do Not settle for a plain jane symetrical dish. What you need is a D-dish, aka Inverted dome aka Reverse dome.

As for rings --- don't settle for old-fashioned thick tractor rings like 5/64, 5/64, 3/16 as were OE in most sbc.
Instead, use much thinner rings; preferably a Metric ringpack.

FWIW, later ringpaks typically have a Steel top ring (instead of iron). When steel, it can ( & usually does) have a markedly narrower radial wall thickness; thus can more readily flex to conform to cylinder wall --- all the while providing superior sealing without need of power robbing hi-tension (hi-friction) rings. Budget pistons with thick rings --- don't do it.

If your budget allows, do choose a forged piston instead of cast or hyper.
 




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