compression ratio

General engine tech -- Drag Racing to Circle Track

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Tuner
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Re: compression ratio

Post by Tuner » Tue May 22, 2018 6:41 pm

zums wrote:
Tue May 22, 2018 6:11 pm
Tuner wrote:
Tue May 22, 2018 5:14 pm
I have found significant power increase with less than 30 degrees, in fact mid 20's at the torque peak. If you can get on a chassis dyno you may find your engine wants the timing to advance from the torque peak to the power peak. Recent experience is a dirt oval track 355, 13.8/1 comp ratio, 100LL w/MMT, GM marine DP spread bore intake that fits the large port head, Qjet carb, GM 140 cam, likes 24 at 4000 with the advance slope to 29 at 7000, the advance will go to 30 at 8000. With this advance setup the torque is flat like a billiard table and the power is still climbing at 7000 but it doesn't need to turn more than that to win. More than 24 at 4000 hurts the torque. All the stuff interwevbzsez don't work, ports are too big, dual plane has no power at high RPM, Qjet is junk, HEI has weak spark above 4000, 140 cam has too much duration and not enough lift, etc. etc. ….... ha... joke's on the intervbez and the rest of the field. They hate the Qjet. When they come over to see what yards them 1-1/2 lengths from the flag to corner entry they just walk off mumbling and shaking their heads. LOL Answer truthfully what cam is in it and get accused of lying. The internet has people's heads so screwed up it is almost impossible to have an intelligent conversation at the race track nowadays. Did you know race engines are supposed to idle all slobbery and stink up the shop and foul plugs if you drive them too much in the pits?
So your comparing a 13.8 355 to the OPs 9.4 355 with close to the same in, duration @.05
Tom
I'm not comparing anything, just answering novadude's question, "In you experience, what total advance generally works best with Vortec / fast burn style chambers? .. etc." I related a recent experience. Your mileage may vary. The "Fast Burn" heads make best power with significantly less timing than most people normally associate with 23 degree heads. It is as simple as that.
novadude wrote:
Tue May 22, 2018 3:12 pm
Tuner wrote:
Tue May 22, 2018 2:51 pm
How much ignition timing? These heads are "fast burn" and do not need or want as much advance as is commonly used with other Chevy heads.
Not to de-rail this thread... I think this is on-topic....

In your experience, what total advance generally works best with Vortec / fast burn style chambers? I'm running mine at 33 total, and I guess I've never really tried using less total advance. Maybe I should?

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Re: compression ratio

Post by novadude » Wed May 23, 2018 12:21 am

Tuner... thanks... I'll have to try a slower curve and/or less total timing and see how that works out.

Also, Thanks for the story about the engine combo with the qjet and '140' cam. I love seeing guys make 50 yr old GM stuff win in 2018. I'll bet that old GM cam is much easier on springs than the comp trick-of-the-week grinds the rest of the field is probably running. LOL

Sorry to the OP if we got off topic, but it seems like this fits since we are talking vortec chambers and timing.

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Re: compression ratio

Post by 88bluestar » Wed May 23, 2018 2:19 am

I appreciate the comments. Car is geared up quite a bit for such a small track. Just to far big of cam and head for now.

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Re: compression ratio

Post by F-BIRD'88 » Wed May 23, 2018 12:02 pm

The good old "140 off road cam" can be a very good cam in a engine that it matches.
Especially if when used with higher ratio rockers (1.7 ish) as the cam lobes are the same as the first L-88 BBC cam. On a very high compression ratio SBC 355 the 112LSA is good.

A 13.8:1 cr SBC will need less spark advance at WOT than say a 9:1 cr 355.
Using 100LL on this is suspect for spark knock limit ( requires less timing at some points to avoid knock. )
On your 9-10:1cr SBC with vortec heads: if you are using a GM HEI distributor that is locked out it will self retard at least a bit at high rpm from what you set the timing at at idle.
So a 36deg setting self retards to like 32-33 deg when at high rpm. So set your timing accordingly.
But do not use excessive spark advance...
I have always used about 35deg on my vortec headed motors ( with a HEI distributor) so...

You can probabily bump the cr up .6 by just swapping the head gasket (.015" felpro steel shim gasket) It sure will not slow it down any. Move the cam too. It is up to you to find the sweet spot. The head is not too big if when used with a BIG Dual Plane manifold and the cam is in its sweet spot for this car. You have to find that by track testing.

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Re: compression ratio

Post by Tuner » Wed May 23, 2018 1:46 pm

F-BIRD'88 wrote:
Wed May 23, 2018 12:02 pm
The good old "140 off road cam" can be a very good cam in a engine that it matches.
Especially if when used with higher ratio rockers (1.7 ish) as the cam lobes are the same as the first L-88 BBC cam. On a very high compression ratio SBC 355 the 112LSA is good.

A 13.8:1 cr SBC will need less spark advance at WOT than say a 9:1 cr 355.
Using 100LL on this is suspect for spark knock limit ( requires less timing at some points to avoid knock. )
The engine I described above has the cast iron Bowtie Vortec Fast Burn heads (I think GM 19331472). You can suspect 100LL w/MMT if you wish, your suspection only means you do not know. This engine, on this fuel, does not knock with more timing, it simply does not make as much power. Particularly interesting is how much less it wants at the torque peak than at the power peak. This appetite for timing has been checked, A-B-A-B with the same heads, same cam, intake and carb, on two short blocks, last year's 388 and this year's 355. Same deal with both short blocks, wants less advance at torque peak than power peak. (as do most engines)
On your 9-10:1cr SBC with vortec heads: if you are using a GM HEI distributor that is locked out it will self retard at least a bit at high rpm from what you set the timing at at idle.
So a 36deg setting self retards to like 32-33 deg when at high rpm. So set your timing accordingly.
But do not use excessive spark advance...
I have always used about 35deg on my vortec headed motors ( with a HEI distributor) so...
..... so, you have been using too much timing for the standard production Vortec head, which is usually happy with 30~32, however, and more important, do not confuse the standard production Vortec head with the Fast Burn performance versions, iron and aluminum, which require much less spark advance.
You can probabily bump the cr up .6 by just swapping the head gasket (.015" felpro steel shim gasket) It sure will not slow it down any. Move the cam too. It is up to you to find the sweet spot. The head is not too big if when used with a BIG Dual Plane manifold and the cam is in its sweet spot for this car. You have to find that by track testing.
Further interesting, this year's 355 with 30 less cubic inches than last year's 388 makes 30+ more HP and 20+ more ft. lbs. torque on the same chassis dyno. Significant differences are: fresh valve grind, polished cylinder walls with 400 wet-or-dry, 1mm rings, different oil pan, everything else, headers and muffler, is the same.

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Re: compression ratio

Post by groberts101 » Wed May 23, 2018 2:27 pm

Since we're already so far removed from the orginal question anyways.. I think Tuner may be confusing the pre-'96 Vortec designs with the later '96+ L31 fast burn chamber designs? Because in reality those bigger port GMPP chambers are not all that much different(aside from the spark plugs squish pad shape) and with near identical chamber sizes as well.

The other thing that, which has already been implied, when comparing a lower compression/powered engine to another with MUCH higher compression/power.. is the fact that much of the engines total ignition lead requirements hinge upon the mixture density AND mixture speed.

So higher compression(tighter packed fuel molecules and increased mixture motion), higher powered(denser mixture/tighter packed fuel molecules), and higher engine speeds(potentially even denser mixture/tighter packed fuel molecules due to increased VE AND faster mixture motion) can and usually will equate to less ignition advance requirements than another less potent motor would like to have for best power throughout its curve.

In that respect, I highly doubt this OP's motor will make more power under 30° and I'd wager small cash he'll likely end up in the low to mid-30's depending on how far down into the rev range the motor is pulled down in the corners.

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Re: compression ratio

Post by Tuner » Wed May 23, 2018 3:47 pm

I'm not confused about anything I've posted, though there seems to be confusion about what you think you read. This is simple. The GM Preformance Large Port Cast Iron Bowtie Vortec Fast Burn head requires less timing than other 23 degree SBC heads, including other GM heads described "Vortec" and "fast burn", such as the L-31. It would be good if someone else who actually has experience with these GM Performance heads and has experimented with timing will share what they have learned.

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Re: compression ratio

Post by CGT » Wed May 23, 2018 4:03 pm

Tuner wrote:
Wed May 23, 2018 3:47 pm
I'm not confused about anything I've posted, though there seems to be confusion about what you think you read. This is simple. The GM Preformance Large Port Cast Iron Bowtie Vortec Fast Burn head requires less timing than other 23 degree SBC heads, including other GM heads described "Vortec" and "fast burn", such as the L-31. It would be good if someone else who actually has experience with these GM Performance heads and has experimented with timing will share what they have learned.
I mostly have seen what you have seen as far as timing on the BV and GM fastburn heads (on 383 cubic inch engines....28-32 degrees of timing runs about the same, a little more torque..sometimes around peak torque with less, but not always. And have seen the lesser timing below and at peak torque be better on a lot more things than just BV heads.

The shorter stroke, lower compression stuff with those heads generally will want more than that as most do. My personal 355 with fastburn heads, 10.5:1 likes considerably more than that, closer to 40. Edit: My 355 had BV heads on it with 40°...it now has fastburn heads awaiting to be dynoed

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Re: compression ratio

Post by F-BIRD'88 » Wed May 23, 2018 4:18 pm

Keep your shirt on there Tuner... Its all good. Would be interesting to know more about the motor u used the "140 cam" in .... Power RPM torque, RPM etc more details Rockers etc.
Tell us what you did with it.

your post are always appreciated.

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Re: compression ratio

Post by Tuner » Wed May 23, 2018 4:53 pm

1.6 rockers, don't have the numbers here to quote, but it has such a flat torque curve over such a wide RPM range it has several of us railbirds shaking our heads, looking at each other and saying, "Huh, aint that something." I don't know what to say, it just does. Probably the less than ideal factory GM dual plane intake and the QJet, ya think? The dyno is 25 miles from here and I have no other reason to visit until next week, so maybe then can say some specific numbers.

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Re: compression ratio

Post by zums » Wed May 23, 2018 6:55 pm

Tuner wrote:
Wed May 23, 2018 3:47 pm
I'm not confused about anything I've posted, though there seems to be confusion about what you think you read. This is simple. The GM Preformance Large Port Cast Iron Bowtie Vortec Fast Burn head requires less timing than other 23 degree SBC heads, including other GM heads described "Vortec" and "fast burn", such as the L-31. It would be good if someone else who actually has experience with these GM Performance heads and has experimented with timing will share what they have learned.
Well the Fast Burn, which is GMPP aluminum head has a completely different chamber than what you are calling fast burn iron vortec heads, which do share a very similar chamber as the L31
Tom

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Re: compression ratio

Post by Tuner » Wed May 23, 2018 7:52 pm

I don't know what to tell you except what are you arguing about? I guess you can have it your way if you want, but GM calls it "Fast Burn", so I suppose if GM calls it "Fast Burn" everybody but you can call it "Fast Burn", do you think?

For a head that you want to say is not a "Fast Burn" design it sure runs good with I guess what y'all are saying is not enough spark advance, and if it has any more than "not enough" it makes less power.

Image

Large-Port Vortec Bowtie Head Assembly

19331472

Product Details

VORTEC BOWTIE CYLINDER HEADS
Vortec Bowtie cylinder heads are the most powerful cast-iron heads offered by Chevrolet Performance. These upgraded production cylinder heads are ideal for 400-450 horsepower street and racing (great for circle track applications) engines. Vortec Bowtie cylinder heads come with bigger valves, a thicker deck surface and 66cc combustion chambers. The heads provide outstanding low-lift flow numbers (the more air you flow, the more potential power) and Fast Burn performance all in an affordable, cast-iron head.

Vortec Bowtie Cylinder Head Technical Notes:
• Cast-iron Large Runner Cylinder Head
• 66cc combustion chambers
• 0.450" deck thickness
• Hardened exhaust valve seats
• Machined for 2.000"/1.550" valves
• Maximum 0.530" valve lift (without modifications)
• Straight spark plug design
• No heat risers
• Drilled and tapped for 7/16"-14 screw-in studs
• Dual bolt patterns for Vortec and early style intake manifolds (early model P/N 10051103; Vortec intakes P/N 12366573, 12496820, 12496821, 12496822 or 12489371)
• Use intake gasket P/N 89017465 for Vortec intakes or dual pattern intake gasket P/N 19301685 for early model intakes or Vortec design intake manifolds
• Dual bolt patterns for perimeter-style and center-bolt valve covers
• Vortec intake manifold three-step torque specs: 2 lb.-ft.; 9 lb.-ft.; 11 lb.-ft.

Large-Port Vortec Bowtie Head Assembly
• Completely assembled, ready to bolt-on
• Improved air flow (281 cfm @ 0.600")
• 225cc intake ports
• 77cc exhaust ports
• 65cc combustion chambers
• Use Fel-Pro® P/N 1470 exhaust gasket (minor trimming may be necessary)
• Bare head P/N 19331473, available separately
This head is assembled with the following components:
12555331 Intake valves (4)
19301708 Valve spring retainers (8)
12551313 Exhaust valves (4)
19301709 Valve stem key (16)
12625033 Valve springs (8)
12552126 Valve rocker arm studs (8)
19301707 Valve spring seats (8)
10168519 Valve guides (8)
10212810 Valve stem seals (8)
12346004 Valve rocker arm stud sealer

zums
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Re: compression ratio

Post by zums » Wed May 23, 2018 8:12 pm

Tuner wrote:
Wed May 23, 2018 7:52 pm
I don't know what to tell you except what are you arguing about? I guess you can have it your way if you want, but GM calls it "Fast Burn", so I suppose if GM calls it "Fast Burn" everybody but you can call it "Fast Burn", do you think?

For a head that you want to say is not a "Fast Burn" design it sure runs good with I guess what y'all are saying is not enough spark advance, and if it has any more than "not enough" it makes less power.

Image

Large-Port Vortec Bowtie Head Assembly

19331472

Product Details

VORTEC BOWTIE CYLINDER HEADS
Vortec Bowtie cylinder heads are the most powerful cast-iron heads offered by Chevrolet Performance. These upgraded production cylinder heads are ideal for 400-450 horsepower street and racing (great for circle track applications) engines. Vortec Bowtie cylinder heads come with bigger valves, a thicker deck surface and 66cc combustion chambers. The heads provide outstanding low-lift flow numbers (the more air you flow, the more potential power) and Fast Burn performance all in an affordable, cast-iron head.

Vortec Bowtie Cylinder Head Technical Notes:
• Cast-iron Large Runner Cylinder Head
• 66cc combustion chambers
• 0.450" deck thickness
• Hardened exhaust valve seats
• Machined for 2.000"/1.550" valves
• Maximum 0.530" valve lift (without modifications)
• Straight spark plug design
• No heat risers
• Drilled and tapped for 7/16"-14 screw-in studs
• Dual bolt patterns for Vortec and early style intake manifolds (early model P/N 10051103; Vortec intakes P/N 12366573, 12496820, 12496821, 12496822 or 12489371)
• Use intake gasket P/N 89017465 for Vortec intakes or dual pattern intake gasket P/N 19301685 for early model intakes or Vortec design intake manifolds
• Dual bolt patterns for perimeter-style and center-bolt valve covers
• Vortec intake manifold three-step torque specs: 2 lb.-ft.; 9 lb.-ft.; 11 lb.-ft.

Large-Port Vortec Bowtie Head Assembly
• Completely assembled, ready to bolt-on
• Improved air flow (281 cfm @ 0.600")
• 225cc intake ports
• 77cc exhaust ports
• 65cc combustion chambers
• Use Fel-Pro® P/N 1470 exhaust gasket (minor trimming may be necessary)
• Bare head P/N 19331473, available separately
This head is assembled with the following components:
12555331 Intake valves (4)
19301708 Valve spring retainers (8)
12551313 Exhaust valves (4)
19301709 Valve stem key (16)
12625033 Valve springs (8)
12552126 Valve rocker arm studs (8)
19301707 Valve spring seats (8)
10168519 Valve guides (8)
10212810 Valve stem seals (8)
12346004 Valve rocker arm stud sealer
Fast Burn Aluminum Cylinder Head Assembly
19300955
Your Price: $851.47
Suggested Retail: $1004.09


1


PRODUCT DETAILS
ALUMINUM FAST BURN HEADS
Chevrolet Performance’s Fast Burn 23-degree cylinder heads deliver maximum performance for Small-Block engines. An aluminum head casting – distinguished by Chevy Bowtie logos at each end – and a valvetrain with high-rpm, LS-style beehive-type valve springs stretches the performance range of the heads to enable greater power at a higher rpm! Fast Burn technology delivers more horsepower by increasing cylinder pressures, which maximizes the air/fuel mixture’s combustion. The 62cc combustion chamber is designed for use with flat-top pistons. The CNC-machined Fast Burn heads require no additional porting for optimal performance, so all you need to do is bolt them onto your Small-Block and go! They can be used on any Small-Block engine with at least 4.000-inch bores and the standard-flow coolant system. Not for use on Gen II 1992-96 LT1/LT4 engines with reverse-flow cooling system.

Fast Burn Aluminum Cylinder Head Assembly
• CNC-machined aluminum performance cylinder head
• Completely assembled with 2.000"/1.550" valves
• 210cc intake port, roof raised .240"
• 78cc D-shaped exhaust ports, raised .200" – requires Fel-Pro® exhaust gasket P/N 1470 (may require minor trimming)
• 62cc combustion chamber, .400" deck (can be milled to .060")
• No heat riser
• Angled spark plugs (5/8" hex, 3/4" reach, tapered plugs)
• 1.48" valve spring seat diameter
• Use head gaskets with stainless steel fire rings
• Raised, machined rocker rails
• .530" maximum valve lift (without modifications)
• Screw-in studs (3/8" top, 7/16" bottom)
• New “time-serts” prevents oil migration through rocker studs
• Dual bolt patterns for perimeter-bolt and center-bolt valve covers
• Dual bolt patterns for Vortec and early-model intake manifolds
• Use bare head P/N 19300956
• Use production intake gasket P/N 19301685

This head is assembled with the following components:
12555331 Intake valves (4)
19301708 Valve spring retainers (8)
12551313 Exhaust valves (4)
19301709 Valve stem key (16)
12625033 Valve springs (8)
12552126 Valve rocker arm studs (8)
19301707 Valve spring seats (8)
10168519 Valve guides (8)
10212810 Valve stem seals (8)
12346004 Valve rocker arm stud sealer

Not arguing, just trying to figure out what head your talking about
Tom

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Re: compression ratio

Post by Tuner » Wed May 23, 2018 8:43 pm

I guess you'll need somebody to read the thread to you, I put the part number on this page twice. #-o

I'll put the timing wherever you guys say, if you all agree to buy the replacement parts. (and protect me from the driver when it slows the car down) :roll:

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Re: compression ratio

Post by groberts101 » Wed May 23, 2018 10:04 pm

No need to be so sensitive about someone disagreeing with mid-20's being an optimized # on a lower performance 9.xx compression combo. And I'm well aware of what those heads look like and I've also tuned motors running them several years ago as well.

The ONLY reason I questioned your comparison of these heads being so far removed from the L31's.. is because aside from port sizes.. they are not that far apart. On my phone now but google a pic of the L31 chamber to get my point. Aside from minor variation in spark plug squish pad design.. they are nearly identical. That's all I was getting at really.

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