[loosend]

I've previously posted here with an engine/converter combo that per your feedback, needed to be refined. Especailly concerning my bull-headedness about using an 11" converter. I have refined it to as follows:
357 (350 @ .040 over) 4 bolt mains
-Forged flat top pistons with 4 valve reliefs (6cc?)
-Deck height should be stock: .025 estimated (will check when I tear down and make adjustment to the gasket thickness as needed)
-Head gasket: .015 compressed (Felpro embossed steel shim) - 4.100 gasket bore holes
-AFR aluminum 195 heads flat milled to a 62cc chamber
-UD/Lunati Cam SB288/288F10 110 LSA w/ .540 lift and 255 dur @ .050 using .026 lash
-Victor Jr intake
-Holley 3310 750cfm Vac. Secondary
-MSD 6AL ignition with 7,000 or 7,200 rpm chip and MSD distributor w/o vacuum advance
-Heddman 1 ¾” Primary Coated Headers with 3” collectors
-2 ¼” exhaust pipes
-3.90 12 bolt W/posi
-Built Turbo 350 trans w/ Case Saver and Valve Body Plate
-10" ATI #408340 converter 3,200 to 3,500 stall

The above gives me a 10.55 compression ratio with the 62cc combustion chamber

What DCR will this cam produce or should I go to 284/284F10? I have tried using the formula and embarrassingly, I am lost. The numbers I get do not make sense. The single pattern cam is to help with lower end torque at the sacrifice of some upper RPM's.

 

[427L88]

w/5.700" rods its 8.07. Whoops, on a 104 icl, it's 8.208. 8.384 with the 284 though ( @104icl). With your quench and heads, hmmm..... 8.3 would need good fuel, but ...

Stout combo!

 

[Nickel333]

remember though, harold rates his solid cams @.020 in stead of the standard .004-.006 so take that into concideration, his 288 is probably equal to a comp at 295 or so. your DCR would be less, if you want good info on DCR with these cams go to the camaro page and page "Eric68" hes very knowledgeable about this. I would also go with a 2.5" exaust pipe over the 2.25, and a 750 3310 holley may not be the best choice with that aggressive of a cam. Id have to think a mighty demon {maybe 650} would be your best bet, but youde have to call demon to check on that.

 

[Pat Kelley]

Originally posted by Nickel333:
remember though, harold rates his solid cams @.020 in stead of the standard .004-.006 so take that into concideration, his 288 is probably equal to a comp at 295 or so.

Yes, Harold rates his wide lash solid cams at .020". His hydraulics are rated at .004" or .006" like everyone eles. With .026" lash the cam is actually a bit smaller than speced (at .024" lash .020" lift correct). The valve is not coming off the seat until the tappet has lifted .021333>". DCR will be a bit higher than calculated. I don't know how much. If you lash at .024" the specs are correct and 8.208 is the DCR. Should be an excellent performer.

I think a DP would be better but the VS should work well. I'd go with 1-5/8" headers and, at least, 2.5" pipes. Good mufflers like the Dynomax Welded Ultraflows are called for.

 

[loosend]

Would I be better off with a 64 cc chamber on the heads? That gives 10.31 compression. Would that give me more tolerance for 93 octane gas?

Pat--I agree with the 1 5/8" primary header, which is what I have now but they won't fit the AFR head ports, per AFR. It seems I am stuck with going to 1 3/4" primaries like it or not and that is a torque killer, I know.

How will DCR be affected if the cam is put in 4 degrees advanced instead of 6 degrees?

 

[427L88]

More advance = more DCR ( earlier closing of intake)

I think 8.20 at 6 or 8.0 at 4 degrees advance should be plenty OK for 93. You might even get away with 8.3, but that's pushing the envelope. I get away with 8.6, but its close.

 

[UDHarold]

About 4° advance should be the minimum, and 6° is my preferrence. The 288/288F10 will have LOTS of power about 2500 or so.
To take a little away from the bottomend, and to lower the DCR at the same time, run the valve lash at .018" HOT, or about .014" cold. This opens the valve a little sooner, and closes it a little later, for a lower DCR. There is more gain of duration on the closing side(about 2° closing for 1° opening) than on the opening side.
It will also add about a year to the valve spring life, etc, etc, etc.....

UDHarold

 

[Eric68]

Loosend,

I think with 10.5:1 and the UD288 you will not have a problem with pump premium. If anything, you will probably be able to run mid-grade. Like Nick mentioned Harold's cams use .020 for "advertised" duration - so any DCR figure you get using .020 will be pretty conservative (higher than if the cam was rated at .006)

and BTW I like the 1-3/4 headers just fine with your combo, but am not real geeked about the 2-1/4" exhaust pipes

There was an interesting dyno comparison on header tube sizes in one of the recent mags (sorry I can never remember which one) with some suprising results. The 383 engine they tested actally made max avg power with the LARGE 1-7/8" headers They tested 1-1/2" shorties (which also made very good power), 1-5/8 long tubes, 1-3/4, and 1-7/8 headers.

All the results were pretty close . . . the big tube headers did not kill all the power that urban legend says they would and the shorties made very good power -- also flying in the face of conventional thought.

 

[Doug F.]

I've personally seen header changes lose 40 ft/lbs of torque with just collector changes in peaks and dips on low HP engines.

Just because one particular engine does something in a MAGAZINE article, I would not say it is true across the board. Every part depends on the combination and you can't make generic statements about anything.

If you look at those particular numbers, and compared the 1-1/2 to the 1-7/8 or 3/4 for that matter, it lost a LOT of bottom end torque.

I know you realize this Eric.

 

[Eric68]

Doug,

I think there is this stereotype about headers out there that is sometimes misleading. True, big tube headers can kill some low end TQ in certain applications and there is a "bigger is better" mentality out there that is often counter-productive. But frankly I don't think 1-5/8" vs. 1-3/4" tubes on a 400+ HP engine is something to sit and argue about, it just isn't that big of a deal. In this case I think the 2-1/4" (probably not mandrell either) exhaust pipes are costing way more power than the slightly too-large 1-3/4" tubes are.

I'd be interested in any specific data you would like to share on combo, primary size, length, collector size, length, etc -- its an interesting subject. Collector design is something I personally am particularly interested in.

 

[Nickel333]

Doug id like to see the numbers from that 40 lb/ft of torque lost from a header switch.Im not being arogant, i would just like to see what kind of motor we were talking about as i would have to think it would be on the dramatic end of the spectrum. {super mild motor, way too big of headers, sompared to ideal headers}

 

[Eric68]

OK, I dug up the article (CHP - April '04), just so everyone that hasn't seen it knows what the heck I'm talking about The engine was a 450 HP 383 --- typical hot-street type build.

The baseline was with 1-1/2" flow tech intermediate length headers.

The next test was with Hooker 1-5/8" unequal-length long-tube tubes.

* at the lowest test RPM (3,000 RPM) peak TQ was down 14 lb/ft and 8 HP from the shorties.

* The most the engine was down was 29 lb/ft and 19 HP. At higher RPM it was up a max of 12 lb/ft and 12 HP.

* Average TQ was down 1 lb/ft and up 1 HP over the shorties from 3000 to 6000 RPM.

Next test was with 1-3/4 headers and was compared to the 1-5/8" headers

* At the lowest test RPM TQ was up 7 lb/ft (still down 7 from the shorties) and HP was up 4 (still down 4 from the shorties).

* The most the engine was down was 3 lb/ft and 4 HP from the 1-5/8. At higher RPM it was up a max of 7 lb/ft and 8 HP.

* Average TQ was up 1 lb/ft and up 4 HP over the shorties from 3000 to 6000 RPM.

Next test was with 1-7/8" headers and was compared to the 1-3/4" headers.

* At the lowest test RPM TQ was up 8 lb/ft (actually UP 1 over the 1-1/2" shorties) and HP was up 5 (also up 1 over the shorties).

* At the most the engine was up 16 lb/ft and 10 HP over the 1-3/4. In the midrange the 1-7/8 tubes were actually down a little from the 1-3/4 headers and picked up a little at the high end.

* Average numbers were up 1 lb/ft and up 3 HP over the baseline 1-1/2" shorties.

In this case I think the 1-3/4 tube headers made the best average power from 3000 to 6000 RPM. The most interesting part to me was that average power did not change significantly from the smallest to the largest headers tested.

One factor not testable on a dyno is driveability and throttle response. I think the smaller headers would have won that contest if driveability could be measured.

And I think that chassis type/setup would weigh heavily when making the decision on which header to pick -- a heavy, full-frame car would need that extra low end grunt to get out of the hole, so in that case a smaller tube header is clearly the way to go -- with a lighter car and looser stall the bigger tubes would probably be a good choice.

My point ---- just don't assume that smaller (or bigger) is necessarily better in every situation.

 

[Motor Martyr]

What causes the biggest problems is when you put the "two sizes too big" on a motor.
If the optimum header is a 1-1/2" 34" lenght primary with 3" collector of 10" in lenght....and you use a hooker super comp with 1-3/4" primaries, which are typically short (30") and have short collectors....then you're giving up ET.

Not only will it be slow in the 60ft, but coming off the shift's will be slow as well.

The best thing you can do, in this situation, is buy a set of flanges for 1-3/4" tube, bend up 1-5/8" pipes to fit the car, and flare them out to 1-3/4".

You're creating more of a problem by going from a 3" collector to a 2-1/4" pipe....buy/build collectors that are 2-1/2" and build a 2-1/2" exhuast system.

I'll shoot a few pictures of the set i did recently if you like.

I figured the optimum primary dia to be 1-5/8"...so i bought a set of 1-5/8" headers, cut the flanges off, opened up the flanges to match the ports, flared out the pipes to fit the back of the flanges, welded the pipes to the backside of the flanges. Surfaced the flanges, then extended the primaries to roughly 34" (Some are shorter), flared the center section together (similar to how ed henneman does it), then built smooth transisition 3" collectors.
All welds are heli-arc with stainless wire.

I also built 3" pipe out of stainless sheet, and put flanges on the ends of it, so the entire exhuast system is bolt together.

When i get the mufflers, and turndowns i'll be welding 3 bolt flanges on to them as well.