Optimal Dart head selection - Team Camaro Tech
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post #1 of 11 (permalink) Old Jan 3rd, 17, 04:23 PM Thread Starter
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Tony W
 
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Optimal Dart head selection

Happy New Year.

I am considering changing the my stock original heads for a pair of Dart iron eagles. Need some input as to the selection of the most suitable iron eagle head for my current small block

Here's what I have now: Stock 1969 350 rebuild (30 over) , stock 76cc chambers pocket ported with 1.94 valves, hypereutectic pistons, .025 in the hole, .039 head gasket, Comp cam 268 extreme energy - 110 lobe separation angle and 106 centerline. Engine has stock 69 manifold

Static compression is in at 8.5 with the dynamic compression calculated to be 7.1.

The engine is in a 69 camaro, with a stock converter, and Th 350 transmission. Rear gears are stock 308's.

The XE 268 cam simply has too much duration for the current compression level of the stock heads and so I'd like to change to a head that would allow for higher compression and better flow with no detonation issues.

I am looking at purchasing the Dart ss heads with 165 cc runners or Dart iron eagles with 180 cc runners. Wondering what is the best combination of runners and chamber sizes? I plan to buy the bare heads

so I can fit the heads with valve springs that complement the cam I have. Also wondering if I can go with the 67 cc chamber size for the "ss" head or the 64 chamber size with the iron eagle head

Any help will be greatly appreciated.
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post #2 of 11 (permalink) Old Jan 3rd, 17, 04:29 PM
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Don
 
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Re: Optimal Dart head selection

Tony, I ran the dart cast iron heads on a 355 with the same cam setup. I later found I could advance the cam timing some 6 degrees and get more performance out of the motor that I felt the heads did. Of course I was running 373 gears on a 5 speed. I was running the xe 268 comp cam on solids.

To make your motor work, you will need to change your rear gearing to allow this motor or another motor to show its true potential . I would look at gearing first then tune the motor. Just my 2

Don
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Zdld17:69 Z/RS,306, NOR141111, 9N554XXX, 12A, X3G, 59/59,723, AFR 195,CCC282/290HR, TKO 600, BU1122B1E Owner since Dec 1968

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post #3 of 11 (permalink) Old Jan 3rd, 17, 05:17 PM
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Doug
 
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Re: Optimal Dart head selection

Here is the best head you can get to go with your engine. https://www.summitracing.com/parts/d...1111/overview/ These will give you a static compression ratio of 9.405 and a DCR of 7.847. Be sure to use a .015 Fel-Pro 1094 head gasket for a .040 quench.
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post #4 of 11 (permalink) Old Jan 3rd, 17, 09:25 PM Thread Starter
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Tony W
 
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Re: Optimal Dart head selection

Thanks for your response. Glad to hear that you had success with the Dart heads. Do you recall if the heads were the "ss" 165 cc runners or the 180 runners. And do you know what chamber size you used?
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post #5 of 11 (permalink) Old Jan 3rd, 17, 09:56 PM Thread Starter
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Tony W
 
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Re: Optimal Dart head selection

thanks too. I checked out the summit link and saw your recommendation of the Dart iron 72 cc chamber, 180 runner. To get the .040 quench you also recommend the .015 Fel Pro. I have two more questions for you:
1) The XE 268 comp cam recommends springs that have am installed seat pound (pressure) of 105 lb/sqin. The Dart springs are 120 lbs to the seat. Is the difference of 15 lbs. on the seat a big deal in terms of cam life? ; 2) Will the .015 Fel Pro be too thin given that the engine I had rebuilt was not decked but only resurfaced for the stock rebuilt heads? I do agree that the combination of gasket thickness and chamber at 72 does give me the best chance of not detonating. I thought I might need to use at the least a compressed gasket around .028 in.

Let me run another scenario by you. Suppose I use the Dart 180cc with a 64 cc chamber with .028 compressed GM gasket. Static ratio (given 6cc eye brows in the piston) calculates to 9.83, with DCR in a 8.14) Here's the obvious question: am I running into trouble with an iron head at this compression ratio and the less optimal quench?

I have to say, I had not even thought about the 72cc chamber and the 180 runner. If the .015 gasket is a go., I think you've really given me some hope here.
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post #6 of 11 (permalink) Old Jan 4th, 17, 03:15 AM
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Re: Optimal Dart head selection

Good advice above had a set of 72cc 180's on a street driven car and they worked great.

68 Resto-Mod in progress..355sbc .350 Trans Rushforth wheels
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post #7 of 11 (permalink) Old Jan 4th, 17, 05:52 PM Thread Starter
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Re: Optimal Dart head selection

Jonathan Thanks for a second vote for the 72 cc chamber with the 180's. I am going to check with the machinist who surfaced the stock 350 block
to see if I can get away with the Felpro .015 head gasket. I am going to use an edelbrock dual plane manifold with the dart heads to help
with the flow.

When all is done, I'll post the results of the build

Tony
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post #8 of 11 (permalink) Old Jan 4th, 17, 06:27 PM
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Dave
 
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Re: Optimal Dart head selection

Tony if you are curious as to who has the "best" advise consider the factories engineers and what they choose to do with the advantages of fluid dynamic modeling head flow on their own in house super computer.

Consider the "there isn't anything better than Camel Hump heads". Though it is the one hump Arabian (aka Dromedary) camel that rules the Arabian desert not the smaller Asian Bactrian camel that is used asa pack animal. The Fuelie heads that first apeared back in 1962 on the fuel injected Corvette 283 SBC has intake ports that have a volume of 170 cc. By the time Chevy was putting larger displacement 350small blocks in their race ready Corvettes that the intake volume grew to 190 cc. These engines made at least one horse per cube with a solid tappet cam that redlined (that means you could race for twelve hours at Sebring or Watkins Glenn bumping up against it) at 5,600 RPM; this was even though in a drag car you often spun the same LT-1 350 up to 7,800 RPM.

Now consider that a 1.94 intake valve Vortec head will out flow any fuelie head and offer about 40 more horse with no other change.

My 406 had 215 cc intake runners. this is because a 406 is 14% bigger than a 355 so the ports are 12% bigger in size to match the demand of the larger displacement. I increased the size based upon what i learned in school about fluid dynamics: as the volume increases the pressure drops inversley. So a bigger engine needs bigger ports to maintain the same air velocity in the port.

If you are intending to run your 355 at wide open throttle as long as it is in gear ( just think opf how a race car is driven); then you should also condider increasing the port volume to match the increased air flow. This is beacus a 406 that is not spining much more than 4,600 RPM is going to be moving roughly the same volume of air as a 355 spinning 7,800 RPM all day long. Higher RPM equates to more fill cycles per minute so a smaller engine can soon catch up to and pass a larger one. (this was the reasoning used by Chevy engineers when they stuck a 850 cfm Holley on top of a ZZ 302 motor yet put a 780 cfm Holley on top of a 454.

You will need a longer duration cam and stiffer valve springs to rev a 355 that high and to run it at WOT all day long. Now if you are not driving your Camaro like an Ed Roth bug eyed monster T-shirt then consider smaller port volumes and a milder (shorter duration cam). Would I recomend a Fuelie head, not on a bet. Buy a head sized to your displacement, gearing cam and how you intend to drive the car most of the time (not once a year at the track).

Just remember all of those Z/28 owners we all laugh at as they stall their Camaro two or three times trying to back it into a space at the car show. If you drive a race car on the street then it will behave like a race car all the time; ill mannered and with no bottom end torque.

Big Dave
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post #9 of 11 (permalink) Old Jan 9th, 17, 04:47 PM Thread Starter
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Tony W
 
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Re: Optimal Dart head selection

Big Dave

Appreciate the advice to develop an engine that meets the required use of the car over time. This car is built for what I would call mild street - High 14's in the quarter or so.
Would like your input too on my head purchase plan.

Had a chance to talk to the machine shop that performed the rebuild of the original 350 engine. The engine block and current heads were surfaced - no
decking of the block and no milling of the head. Pistons are .025 down in the cylinder with the .039 Felpro gasket. He agreed that the quench is not
optimal but did not think that the current quench - .064 - would lead to detonation issues with a 64 cc iron chamber "if the timing did not exceed 36 degrees, and premium gas
was used and temps did not exceed 180 degrees.

I like the Dart iron eagles 72 cc ,180 heads as a good choice the engine but am concerned about using a .015 head gasket to get the optimal quench. The machine shop guy cautioned,
"if you're going to use a .015 make sure you seal the head gasket on the block. Don't simply mount the gasket dry".

So here's what I am considering as an alternative to the 72 cc head. Using a Dart iron eagle 64 cc head with 180cc and a GM .039 gasket. This set up does not correct the quench but does give me a 9.5 Static with a 7.94 DCR. I am hoping to gain some low end torque on this motor and the 64 cc heads actually raise the current static one full point and almost the same differential with the DCR. Given this static I think I'm out of danger of detonating given the proper timing, premium fuel, and temperature.


Would love your input on this second option.
Thanks Tony
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post #10 of 11 (permalink) Old Jan 9th, 17, 07:45 PM
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Dave
 
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Re: Optimal Dart head selection

You really can not use the stamped steel factory 0.015" thick compressed head gaskets on a used engine without decking the block and surfacing the heads to get them flat and square with the crank centerline. This is because there is the potential for a head (or block) to be warped that much which results in a blown head gasket.

I use heads with a heart shaped combustion chamber (aka "Fast Burn") heads that were designed by Chevy to reduce emissions. In addition to reducing emissions they make more horsepower because the added turbulence of the design mixes the fuel air charge better for a more complete burn.

The reason a Diesel engine is so efficient is that it burns all the way down the bore versus the short impulse an Otto cycle engine gets from the sudden but usually incomplete burn of the air fuel charge at the top of the stroke. If you can improve the combustion efficiency you raise the cylinder pressure that makes more torque that will get your car going further faster.

The newer Vortec heads have a fast burn chamber in addition to raising the ports which gives a straighter shot at the valve for better cylinder filling (another check the block off for government mandated emission requirements as well as extending mileage to meet C.A.F.E. number requirements). The aftermarket saw the power gains offered by these head designs and blatantly copied Chevrolet's design work (literally millions of dollars in R&D was spent to make these improvements), but the aftermarket didn't restrict the valve lift making most out of the box cast heads make more power than any ported and polished 64 cc Fuelie head.

I am old. I got my engineering degree back in 1968 with a slide rule and a couple of CRC math table books. Doesn't mean I don't have a calculator and use a computer today. I am not married to old school technology the way a lot of guys on this board are. You just have to stay off the bottom of the page when selecting a cam and not think that if I buy the heads with the greatest flow numbers you will build the most powerful engine. It is all about the combination, which includes your car. Weight and gearing are a big factor in choosing parts for your engine. Everything has to work together and it is usually a compromise (unless you are independently wealthy).

Big Dave
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post #11 of 11 (permalink) Old Jan 10th, 17, 03:09 PM Thread Starter
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Tony W
 
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Re: Optimal Dart head selection

Big Dave et alii.: I thought as much about the .015 gasket. The machine shop only surfaced the heads and block when mating the two with a .039 gasket (which works well in the current build.

Given the helpful comments above I will hold off on making any engine head change for now and look more closely at making a change in the rear end gears. I'll set how the current engine

performs with a set of 355 or 373 gears. Appreciate what I've learned from you all

Tony
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