Large Vortec bowtie, Engine?

General engine tech -- Drag Racing to Circle Track

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CGT
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Re: Large Vortec bowtie, Engine?

Post by CGT » Wed Sep 19, 2018 11:30 am

Tuner wrote:
Wed Sep 19, 2018 11:12 am
Anyone who has actually run these heads has no comment about the OP saying he used 36 degrees spark advance with this head which GM identifies as "Fast Burn" and advises 28 ~ 32 in the instructions they supply with the part?
I've seen plenty of them run.....a lot of dyno pulls on them. I've seen the 28-32 thing be pretty accurate, and I've seen it not be. I have seen on a 3.48 stroke engine(my own) with quite a bit of testing, where 36° wouldn't be that abnormal.

You also mentioned in a previous post, about these heads requiring less timing below peak torque for best power. I've seen a little bit of that, but not anymore than other things without these heads.

Quite a few things I've messed with have liked a little less timing at and around peak torque, the Bv and fastburn heads are not special in that way. And the difference of a few degrees in that area on milder NA stuff, hasn't been substantial in any way on what I've played with.....smaller single digit gains if anything. In my opinion the the small port Bv would be better suited for the OP's application.

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Re: Large Vortec bowtie, Engine?

Post by Tuner » Wed Sep 19, 2018 12:03 pm

CGT wrote:
Wed Sep 19, 2018 11:30 am
Tuner wrote:
Wed Sep 19, 2018 11:12 am
Anyone who has actually run these heads has no comment about the OP saying he used 36 degrees spark advance with this head which GM identifies as "Fast Burn" and advises 28 ~ 32 in the instructions they supply with the part?
I've seen plenty of them run.....a lot of dyno pulls on them. I've seen the 28-32 thing be pretty accurate, and I've seen it not be. I have seen on a 3.48 stroke engine(my own) with quite a bit of testing, where 36° wouldn't be that abnormal.

You also mentioned in a previous post, about these heads requiring less timing below peak torque for best power. I've seen a little bit of that, but not anymore than other things without these heads.

Quite a few things I've messed with have liked a little less timing at and around peak torque, the Bv and fastburn heads are not special in that way. And the difference of a few degrees in that area on milder NA stuff, hasn't been substantial in any way on what I've played with.....smaller single digit gains if anything. In my opinion the the small port Bv would be better suited for the OP's application.
To be clear, we are discussing oval track racing here, not drag racing, so are you running the dyno sessions with the same water and oil temperatures you see on the track at the end of a race? What water and oil temps do you use in the dyno sessions?

Agreed, these heads are not unique in appetite for an advance curve through the power band, nearly all engines exhibit that characteristic and benefit from a curve advancing from below peak TQ to above peak HP, some engines more than others, some a lot more than others.

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Re: Large Vortec bowtie, Engine?

Post by CGT » Wed Sep 19, 2018 12:11 pm

Tuner wrote:
Wed Sep 19, 2018 12:03 pm
To be clear, we are discussing oval track racing here, not drag racing, so are you running the dyno sessions with the same water and oil temperatures you see on the track at the end of a race? What water and oil temps do you use in the dyno sessions?
Dyno sessions, I wasn't speaking of drag racing or any particular form of racing. Just looking at power a couple thousand before peak torque to maybe a thousand after, recording data, and studying it.

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Re: Large Vortec bowtie, Engine?

Post by Tuner » Wed Sep 19, 2018 12:16 pm

CGT wrote:
Wed Sep 19, 2018 12:11 pm
Tuner wrote:
Wed Sep 19, 2018 12:03 pm
To be clear, we are discussing oval track racing here, not drag racing, so are you running the dyno sessions with the same water and oil temperatures you see on the track at the end of a race? What water and oil temps do you use in the dyno sessions?
Dyno sessions, I wasn't speaking of drag racing or any particular form of racing. Just looking at power a couple thousand before peak torque to maybe a thousand after, recording data, and studying it.
Good, what oil and water temps ??

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Re: Large Vortec bowtie, Engine?

Post by CGT » Wed Sep 19, 2018 12:32 pm

Tuner wrote:
Wed Sep 19, 2018 12:16 pm
CGT wrote:
Wed Sep 19, 2018 12:11 pm
Tuner wrote:
Wed Sep 19, 2018 12:03 pm
To be clear, we are discussing oval track racing here, not drag racing, so are you running the dyno sessions with the same water and oil temperatures you see on the track at the end of a race? What water and oil temps do you use in the dyno sessions?
Dyno sessions, I wasn't speaking of drag racing or any particular form of racing. Just looking at power a couple thousand before peak torque to maybe a thousand after, recording data, and studying it.
Good, what oil and water temps ??
Generally shoot for 180° water and 200ish° oil.

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Re: Large Vortec bowtie, Engine?

Post by randy331 » Wed Sep 19, 2018 1:28 pm

Stroke will affect optimum ignition timing also. Shorter strokes want more timing. Not sure why that is, but that has held pretty true.
I've seen the same heads go to a short block with less stroke and they now wanted more timing, some of it Vortec/fast burn stuff.
It's showed up in ET at the track and on the dyno both, and I've had some others say the same thing.

So the OP having a 3.48" stroke makes me think 36* isn't outta line for a Vortec head.

On a side note, while maybe the small port head would fit the OP situation better, if I was in the OP situation and had the large port Vortec heads and they were good ( not cracked or in need of a bunch of machining), I'd run the heads and make it work.

There are other ways to add bottom end TQ.

Randy

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Re: Large Vortec bowtie, Engine?

Post by 88bluestar » Wed Sep 19, 2018 1:31 pm

I might add I currently have around .076 quench if that matters timing wise? 15 in the hole, .061 thick head gasket from the original owner. Exact paper work says 9.38:1 but I haven't taken the engine apart yet so not for certain. Car is more lively with 36 timing compared to 28-32, ran at around 210 at track speed and 220 on cautions, but my front end was completely blocked off as well. Plan to run it open at the next race so it has more air flow.

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Re: Large Vortec bowtie, Engine?

Post by 6.50camaro » Wed Sep 19, 2018 5:02 pm

Just changing to a felpro 1003 HG should bring your CR up to 9.83 and it will have .020 tighter quench . Better all round and a start in the right direction. Dan

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Re: Large Vortec bowtie, Engine?

Post by MaxFlow » Sat Sep 22, 2018 4:30 am

The problem you are having is not the head. It's the cam is OUT TO LUNCH for that combo. You need to get the static compression on the edge of the rule and the piston at or a little above the deck. 250's .050 duration isn't going to work on a 355cu/in 9:1 engine unless it has a roots blower installed. Look at the cam in the 604 crate engine..........
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Re: Large Vortec bowtie, Engine?

Post by Tuner » Sat Sep 22, 2018 10:15 am

MaxFlow wrote:
Sat Sep 22, 2018 4:30 am
The problem you are having is not the head. It's the cam is OUT TO LUNCH for that combo. You need to get the static compression on the edge of the rule and the piston at or a little above the deck. 250's .050 duration isn't going to work on a 355cu/in 9:1 engine unless it has a roots blower installed. Look at the cam in the 604 crate engine..........
=D>
Camshaft Type (P/N 10185071): Steel hydraulic roller
Camshaft Lift (in.): .474 intake / .510 exhaust
Camshaft Duration (@.050 in.): 208° intake / 221° exhaust

This hydraulic roller tappet cam is used on the 350 ZZ3 & ZZ4 engines.
The duration at lash point in degrees (intake/exhaust) is 275/280
Duration at .050" tappet lift (intake/exhaust) is 208/221
Maximum lift with 1.5:1 rocker ratio (intake/exhaust) is 474/510.
Valve lash is zero/zero and lobe centerline is 112 degrees.

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Re: Large Vortec bowtie, Engine?

Post by Warp Speed » Sat Sep 22, 2018 4:06 pm

MaxFlow wrote:
Sat Sep 22, 2018 4:30 am
The problem you are having is not the head. It's the cam is OUT TO LUNCH for that combo. 250's .050 duration isn't going to work on a 355cu/in 9:1 engine unless it has a roots blower installed.
We've been screwing up for years then! Lol

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Re: Large Vortec bowtie, Engine?

Post by steve cowan » Sat Sep 22, 2018 6:47 pm

Warp Speed wrote:
Sat Sep 22, 2018 4:06 pm
MaxFlow wrote:
Sat Sep 22, 2018 4:30 am
The problem you are having is not the head. It's the cam is OUT TO LUNCH for that combo. 250's .050 duration isn't going to work on a 355cu/in 9:1 engine unless it has a roots blower installed.
We've been screwing up for years then! Lol
i am no expert on the subject,
but i would think if you are compression and lift,rpm limited you would need a decent amount of duration,timing events to trap as much fuel and air (IVC) and timed EVO to clear the the cylinder of exhaust gases especially having a slightly bigger port and limited intake ramming effect and time limited (RPM) to make any form of power.
JAY,
can you share cam details that the limited compression guys use in you area of expertise even just rough duration,LSA considerations,i am trying to remember and please correct me if i am but i think the low compression engines were still turning 85-8600 rpm ??
dont think you will get there with a mild cam :)
steve c

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Re: Large Vortec bowtie, Engine?

Post by F-BIRD'88 » Sun Sep 23, 2018 1:22 pm

Some things you can do....
Try a vortec dual plane manifold instead of the manifold you have..re set the valve lash bigger to decrease running cam duration. If it calls for .016"-.018" lash hot.
Reset at .022"- .024" hot and test for effect.
Comp cams can advice on the lash +/- variance you can try.
Move the camshaft to a more advanced position
Eg: 100 deg intake c/l. This + the lash reset makes the intake valve close sooner. Makes me he cam seem/run as a smaller cam.
Experiment with carb spacers and plenum dividers.
All these will tweek the torque curve.

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Re: Large Vortec bowtie, Engine?

Post by F-BIRD'88 » Sun Sep 23, 2018 1:27 pm

If wen testing with bigger valve lash the car picks up with a impractical bigger valve lash setting eg: .026" or .028" this tells you to get a shorter duration cam
Knock 10 12 deg off the cam (.050").
Get a real vortec single plane and a vortec dual plane
And test compare. Your intake is not optimum.

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Re: Large Vortec bowtie, Engine?

Post by F-BIRD'88 » Sun Sep 23, 2018 1:29 pm

Header collector design can have a noticeable effect.
Get the real CR up where it should be.
(10.5:1++…)

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