[Tom Vaught]

I realize that you don't pay any attention to Details. It clearly shows that I have 14,612 posts and of those 14,000 have been to give you chit. Get it right George! (:>)

Tom Vaught

[Elarson]

Originally Posted by BruceWilkie

Dart heads use 355 because 356 degrades at 200*f vs 355 doesnt begin to degrade until 300 degrees and has a slower drop off rate above 300 than the drop off rate of 356 above 200. IMO that is significant.

Is that a difference in degradation of strength or stiffness?

Eric

[Travis Q]

Tensile.

For the life of me, I can't find a table of the change in Young's Modulus vs temp for aluminum alloys? It's not in any of my materials books.

[Elarson]

MIL-HDBK-5 or Aerospace Structural Metals Handbook both have that. I'll look them up at work tomorrow. I think tensile strength degradation is very alloy-specific but Youngs Modulus roll off is similar for all aluminums. But I could be wrong.

Eric

[GTOGEORGE]

Tom,
You're not givien me sh_t........I think you are Hilarious! LOL



GTO George

[Travis Q]

All I could find was a range in one of my books that gave Young's modulus as 70-79 MPa for aluminum alloys, but gave no indication of change with temp. I will be curious to hear what you find out.

I think that billet is still the way to go for an all-out boosted cylinder head.

[65nss4spdGTO]

Originally Posted by Elarson

Is that a difference in degradation of strength or stiffness?

Eric

So what happens when the head lifts, is it distortion? Are the clamping loads being compromised from the softness of the head?

Calvin Hill
Hill Performance
708-250-7420

[Kevspontiacs@aol.com]

what about using cryogenics to strengthen the alum?

[lemans411]

Originally Posted by Travis Q

EDIT:
Boost for 1250 hp is going to be around 13-15 psi if the engine is intercooled. 1500 hp will come at 20-22 psi. This is based on 455 inches, 6500 rpm, and 100 degree charge air temps.

i must be doing something wrong then...
my 535 made 960 hp @ 13 psi and estimated 12-1300 based on et and weight at close to 20 psi.

heres my combo
535 8.5-1 compression intercooled on e85
e heads sd perf 330 cfm @ .700
91mm turbo csu 850
cam is .600 lift 268/272 @ .050
car ran best of 9.41 @ 145.58 17-18 psi 4100 pounds!
log manifolds may be holding me back some very similar to v869tr6's


also are you saying larger flowing heads wont make more power ? or just not at less boost? less heat? whats the benefit of more flow on a turbo car. i assumed more na power = more boosted power . am i wrong?

[Jack Gifford]

Originally Posted by Travis Q

... which compromises the clamp load of the center three of the top row of studs...

Travis- I don't share your concern for the head fastener locations; can you elaborate on that? From my dealings with it, my conclusion is that Pontiac created a very intelligent layout.

Thanks for all your valuable contributions to these PY discussions.

[73 TRANSAM]

Is it necessary to run a reverse split cam for a turbo setup? Let's say you have a single turbo T6 with the Gtrim ex housing. I heard from Mark at Bullet to run it a single pattern and if you ask Cam Motion they wanted a reverse split. This is for a 270 cfm exhaust. Also with SS tubular headers.Thanks in advance.

[Travis Q]

Originally Posted by Jack Gifford

Travis- I don't share your concern for the head fastener locations; can you elaborate on that? From my dealings with it, my conclusion is that Pontiac created a very intelligent layout.

Thanks for all your valuable contributions to these PY discussions.

Sure, Jack...

The center top row sees a ton of heat from the two siamesed exhaust ports, as does the lower bottom row center bolt. When the material around the bolt gets hot, it loses stiffness, which causes the clamp load on that bolt to go away. The other bolts that are a concern are the ones that are directly between the intake ports on the top row. Theres not much material around these bolts to provide column strength, and even less is present after port work.

[BruceWilkie]

Really depends on size of cam and where timing points fall. Cam motion appears to have reverse split on every turbo grind they do...Bullet looks at the package and uses what they have had success with. Long standing split on YB as to what works, but I see lots of folks sayin call Mark. I've only spoke with him once and have dealt with Tim at Bullet. Both are capable guys.

My own simulations indicate either single pattern or reverse split depending on ex capability of the head in most situations. Intended use also plays and all out race in some apps might actually benefit from a small split where ex is greater than intake. Largely influenced by intake flow capability vs the exhaust side. Timing points and overall overlap "window" play here...you cant look at just .050 duration and say I'll put that on xxx LSA with xxx ICL. Not all turbo grinds need to be 114 or more LSA as the installed position or true timing more specifically is what really matters.
The actual net valve seat time has effects and can even have different center points than those measured at .050" cam lift.
Travis made some suggestions earlier that are quite sound...but there are always opportunities to find improvements with something a bit different.

All this said picking the right turbine and A/R is more critical than the cam timing as it directly impacts pressure differentials seen at the valves.

[slowbird]

Originally Posted by Travis Q

Sure, Jack...

The center top row sees a ton of heat from the two siamesed exhaust ports, as does the lower bottom row center bolt. When the material around the bolt gets hot, it loses stiffness, which causes the clamp load on that bolt to go away. The other bolts that are a concern are the ones that are directly between the intake ports on the top row. Theres not much material around these bolts to provide column strength, and even less is present after port work.

Travis you ever look into doing a port intruder type deal for the those 2 intake head bolts and also the center exhaust head bolt? That would put the clamping load right on the deck and should have very good column strength there and not effect by the exhaust heat as much.

[Elarson]

From Aerospace Structural Metals Handbook:

355-T61 - yield strength is essentially flat (at 35,000 psi) up thru 300 degF and then drops like a rock above 400 degF. Youngs Modulus (stiffness) is 10.2e6 psi at room temp. No data on temp degradation.

356-T61 - yield strength is lower....30,000 psi at room temp (RT), 28,000 psi at 200 degF and 27,000 psi at 300 degF. It also falls off the edge of the earth above 400 degF. Youngs Modulus is 10.4e6 at room temp, 10.1 at 200 degF and 9.7 at 300 degF. Stiffness also drops fast once you get over 400 degF.

6061-T6 (typical billet) - yield strength is 40,000 psi at RT, 39,000 psi at 200 degF, 37.000 psi at 300 degF and really drops off above 500 degF. Youngs Modulus is 11e6 at room temp, 10.5 at 200 degF and 10.2 at 300 degF. Stiffness also drops fast once you get over 500 degF.


So....
356 is the weakest of the bunch; especially at the higher temps.
356 is slightly stiffer at RT than 355, but probably not enough to matter
6061 wins on initial strength, initial stiffness and upper temp limit.

I tried to do as close to an apples-to-apples comparison as I could. It's important to note that the cast alloys have a tremendous variation in their properties based on casting techniques and heat treatments used. For instance, the whole range of different types of 355 is 18,000 psi to 37,000 psi (yield strength at RT).

Hope this helps,
Eric

[Elarson]

Originally Posted by slowbird

Travis you ever look into doing a port intruder type deal for the those 2 intake head bolts and also the center exhaust head bolt? That would put the clamping load right on the deck and should have very good column strength there and not effect by the exhaust heat as much.

Here's the downside to clamping on the deck instead of the top of the head. The clamp load "wants" to spread out below the fastener in roughly a 45 degree cone. Clamp down on a 1" thick plate and the clamp load is most effective in an area 1" outboard of the fastener head. Clamp down on a 4" thick piece of plate and the clamp load spreads out 4" beyond the fastener head. Ideally, you would want to look down on the head and "see" all of the cones of clamp load overlapping each other and giving nearly full coverage to the head gasket. The closer the fasteners are to the deck, the smaller the effective gasket clamp area under the fastener.

As a second exercise, imagine that 45 degree cone under each bolt and then visualize how the ports cut thru the cone and defeat the natural spread of clamp load.

Eric

[v869tr6]

But I would think if you heat 4" of aluminum it will crush the gasket more then a 1" will.
The only head bolt I find to have loosened up with my E-heads and Cometic gaskets is the one on the lower side between the 2 exhaust ports but that hole also caves in on the stud.

[Elarson]

You're correct that 4" of aluminum would expand 4x more when heated compared to the 1" of aluminum.

Aluminum strength (as noted) really dies above 400 degF so the material around the center exhaust bolt hole collapses when severly heated (and it's strength drops below the stress imparted by the preloaded fastener) and then when the head cools and the aluminum shrinks, you have no clamp load left. Getting exhaust heat away from the aluminum under the bolts is the cure.

<cough> Ram Air 5 <cough>

Eric

[v869tr6]

So what does a Ram air 5 head cost? If made up in numbers more then a few and maybe even in cast iron?
Looking at the bolt thru the port wall on a RA5 on a different thread doesn't look good for clamping, but a turbo head isn't going to need all the porting.
Also what would it take to make a hemi head again and what is the reason they aren't made now?

[Elarson]

Our head is a billet, specifically tailored for nitro. We didn't need the thinwall Pro Stock-type porting job either.

The McCarty RA5 head is a casting. I believe DCI has one in the pipeline too. You would have to ask them what their as-cast wall thickness is around the bolt holes and what they're selling for.

KRE has a hemi design. I don't know if they have them on a running engine yet and I don't know how thick their walls are around the bolts. I believe the main challenge for the Pontiac hemi is getting a workable pushrod geometry. Steve Barcak and Jack Gifford could probably talk at length on that topic.

All things that would be interesting to know.......

Eric