Head too big???

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Head too big???

Post by dragula » Thu Aug 24, 2006 6:07 pm

Just got a 468, will be used for mild street pump gas deal. Has untouched 345cc merlin iron heads, which I know are way to big for this 6000rpm monster. (came with the deal) However, if I decided to keep them for the future I would run them for now. What would be the best way to compensate for the head overkill for lowend driveabilty? I figured on a smaller dualplane and carb, but what about cam? C/R will be around 10:1.

Matt Shaw

PS--Good deal on oversized merlin heads!!! :)

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Post by 67RS502 » Thu Aug 24, 2006 6:30 pm

Concentrate on things that make the engine efficient and will make power everywhere in the powerband, good induction & exhaust.
A oval-port Dart single plane, with a 4-hole spacer and a HP950 carb.
1 7/8" headers. Cam could be puny small and it will still rev past 7000.
67 camaro
girly rollers on pumpgas:
420 - 641hp BretBauerCam, 1.39, 9.79 @ 137.5
383 - 490hp 224/224, 1.56, 10.77 @ 124.6
502 - 626hp 252/263, 049s 1.44, 10.08 @ 132.7
62 Nova cruiser
383/200-4R/12-bolt w 373s
224/224 HR cam
1.57 10.97 @ 121.2


heads too big

Post by awesomebill » Fri Aug 25, 2006 7:00 am

had a customer insist on using his 345 fully ported Merlin heads, beautifully done I may add, on his 66 Chevelle and his brand new 468. I told him not to but he insisted. We assemgled it and at that time I was changing dyno's so we decided to let the track tell us. The engine was full race with a good roller, high comression etc. 3300 lbs 11.00 is all the dog would get. He was very dissapointed. I talked him into a money back deal if my head choice would not work. I purchased a set of 310 cc Canfield units and just installed all his stuff right into the heads. Did not change anything else. The very next Friday night, I drove the car to a 10.004 and was driving right threw the converter. 1 second is a ton. We tried everything to make the big headed 468 run and it was not going to happen.

My suggestions would be to keep the cam smaller on the exhaust side and a very small header with your dual plane and even a 650 cfm carb for the best performance. Not a whole lot you can do without filling the runners in.


Post by dragula » Fri Aug 25, 2006 7:38 am

Thanks you Bill, my thoughts exactly.

Heads for Sale!!! :)


Post by Ed-vancedEngines » Fri Aug 25, 2006 8:30 am

I have a little bit of a problem now like that.

I have a customer with one of Bill Mitchell's Merlin 509 cu in engines with low compression (like supposed to be 9 1/2 - 1) JE Pistons and he is now the proud new owner of a fully modified set of the Pro 1 Darts that are flowing big time numbers in the intake and the exhaust. By the numbers and the flow pattern they could be some prety good N2o heads but this thing will have a 110 LSa Cam of the mid .600's in lift and not much in the duration dept either. Maybe that will help those huge heads.

This is one of those deals that he has the cam the heads the pistns etc that he wants to use. So I can just muddle through and try to do what I can with heads too big for his needs.

I've gotta make this thing launch and recover after the shifts. I have a feeling the velocity will be almost zilch on this combination that is not of my choosing.
flow numbers and specs on the Dart 320 heads that I will have to be using.
I am also included the info on the new Doug Herbert cam.
New cam info spring info
Part# CBH7
2.00 Installed Height RPM Range: 2700-6700

Advertised Duration: 271/283
Duration @ .050: 242/244
Lift: .642/.663
Lobe Center: 110c
Valve Lash .014-.016
Center line 106
@ 050 INT. Open 16 close 45
Exh. Open 53 Close 11

Intake Flow numbers from baseline to ported

Lift " Baseline intake" "Ported intake"
.200 140 150
.300 200 220
.400 235 270
.450 278 310
.500 296 318
.550 303 335
.600 320 348
.650 352 365
.700 360 378
.800 362 393

Exhaust Flow numbers from baseline to ported

Lift " Baseline Exhaust" "Ported Exhaust"
.200 114 130
.300 120 158
.400 152 194
.450 179 210
.500 197 246
.550 218 268
.600 241 278
.650 250 284
.700 255 293
.800 258 298

Now remember this is using the 9 1/2 to 1 compression ratio that he insists on keeping. Maybe that little cam will save the day some.

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Post by SStrokerAce » Fri Aug 25, 2006 1:37 pm


That 9.5:1 as you know will KILL him something evil, you can't crutch the deal with a cam to help it out, just don't happen.

Why does he want to keep that compression, two points will make that motor so much more responsive and powerfull on pump gas that it's not even funny.

[i]Those of you who think you know it all are particularly annoying to those of us who do[/i]- Penske garage sign @ Indy circa '71



Post by awesomebill » Fri Aug 25, 2006 10:33 pm

Ed don't shoot the horse to quickly. That engine combo will run better than you think. The 509 is a fairly large engine and the head seems to have decent #'s. Use a 1-3/4 header and keep the carb in check and you will be suprised. I'd run it if I had to with no problems. The lower compression will make the pump gas work very well and as we all know, this stuff burns pretty quick. May even help. JMO

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Post by SStrokerAce » Sat Aug 26, 2006 1:56 am

Only way I'm running at pump gas motor at 9.5:1 is with iron smog heads, .120" quench and a 200 @ .050" hyd roller cam.
[i]Those of you who think you know it all are particularly annoying to those of us who do[/i]- Penske garage sign @ Indy circa '71

Darin Morgan
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to big!

Post by Darin Morgan » Sat Aug 26, 2006 10:50 am

There is no way to make that deal work well on the street. The low end and mid range will be a DOG! Yes, you can "band-Aid" the thing with dual plane manifold and smaller carb but you will never realize the engines full potential with that large of a head. You need,

More RPM
More Displacement
Smaller heads

I usually run the small oval ports from Dart on the street with some port work done to optimize the system.
Darin Morgan
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Post by PWMAX » Sat Aug 26, 2006 12:27 pm

Some of the best heas for the above 468 engine, are a set of mildy done up 049's, or 781's. They are still plentiful, can be done up for not that much money, and, most important, they flat work. For a street deal, 6000 rpm, you probably won;t find a head thats better. The Brodix heads, or Dart ovals, will work, and the Trick flow ovals, but, not any better, for a lot more money. To bad world messed up their 269cc oval head, by putting the 2.30 intake valve in them. Those were liller done up mild, or street BBC's. If you build a 509 with a 4.5 inch bore, then they work ok, but that big valve does nothing but hurt power, in the "normal" application those heads are designed for


Post by dragula » Sat Aug 26, 2006 5:25 pm

Does anyone here have a decent set of the 049 or 781 's they are trying to part with? Ive found some in my area (all ported so far) but for all I know they were ported by Barney...If anyone has a set I can be reached at 941-626-4715 anytime
Thanks guys,
Matt Shaw

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Post by MileHighMan » Sat Aug 26, 2006 5:59 pm

Hello Matt. If your a little money ahead I'd put the brodix bb1 cyl head on it. I had a set on a 468ci bbc that I sold In january, and god did it run well. corrected to your altitude it would've ran low 10s in a 3400 lbs car. The bb-1 cyl head has a 280cc port. Just right for your 468. Also I traded for a set of heads that I think will perform well on your app. They may be the .049s, or 781s. If you want give me a call and I'll look. 1-505-319-1846.Thanks, and Good Luck. Dan.

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