marky mark

If it were up to you which would make the most sense???

This is for a '69 ragtop, 427 L-36 car with 3:36 rear gear and M-20 tranny in need of a new (or at least rebuilt) motor.

Hood must remain stock bb. Also, all variations would include Hooker Supercomps 1&7/8" primaries, 3" collector and 2 & 1/2" duals w/ X-pipe & Dynomax Super Turbos 2 & 1/2" inlet and outlet.

Here's what I was considering:

1) 502/502 w/ GM alum. oval ports (2.25" intakes), low rise factory L-36 alum intake (spreadbore) and Quadrajet.

2) 502 shortblock with GM alum. rectangular ports (2.25" intakes) that have been milled 30 thous to get up to 9.5 to 1 comp ratio. This would include a factory LS-6 low-rise intake (squarebore) with a Holley dbl pump in the 750-830 cfm range.

3) 502 H.O. (comes with factory rectangular port iron heads). Add LS-6 intake and Holley 750-830 cfm dbl pump. No other changes.

4) 502 H.O. Have heads milled a bit to get comp ratio up to around 9.2 to 1or so (instead of 8.7 to 1). Also, convert heads to adjustable style rocker set-up which would include larger springs, etc.

Did not go with other heads as I didn't want any issues with exhaust ports not lining up, etc.

Not an everyday driver, in general, pleasure driving with occasional "spirited acceleration".

Goal is a fun car that will light up the tires from a 10-15 mph roll in first gear, which is something my 427 (although w/out headers) could not do.

Any thoughts, opinions or suggestions are appreciated!!!

Regards, Mark :flag :chevy

jpatrick636

Marky, I have a 75 with a built up 502 HO, so here is my 2 cents on your plans:

Based upon what you have set as your goal, I would go with number 3. The reason being that whatever you do to increase your compression will be negated by the 2-1/2" exhaust. You are also going to be starved for air with a stock hood. Might as well maintain whatever warranty you get with the motor and go easier on the parts.

According to Holley, 750 is all you need up to 5500 rpm. Tour idle, drivability and throttle response will be best with that carb.

Because the 502 is such a torque monster, the best way to maximize performance in this application (and in my opinion) is on the top end. However that would take you out of your specified goal.

I also strongly recomend: a Centerforce Dual Friction clutch and a Be Cool aluminium radiator with dual Spal fans. No overheating problems!

I do not know offhand what the first gear ratio is for the M-20, I think it is around 2.35. The ideal first gear ratio for a street car is supposed to be 10 to 1. 2.35 x 3.36 = 7.896. You might want to think about that.

I am running with 295/50 15 Goodrich GT's and I don't light up the tires from a roll, I get sideways.

If you want me to run some computer comparisons for you, Email me at jpatrick@firststep.net


[Modified by jpatrick636, 11:20 AM 8/29/2003]

Glensgages

"Survey says: Number One answer on the board! A stock ZZ502/502!"
Idle, torque out the whazoo, warranty; what more could you want? With 3.36s, you'll never get it 'wound-up' to use much more than the stated max RPM of 5200 RPM
Answers # 2 & #3: Why put high-RPM heads, on a low-RPM cammed motor, with a low-rise, dual-plane intake? I'm thinking you'd have the WORST of EITHER worlds...
Answer #4: whacking the heads for increased CR is great, but if you're using the 'mild' H.O.502 cam, why the need for adjustable rockers?
Here's an idea; get the ZZ502/502 in un-assembled form, whack THOSE heads to get higher CR, then assemble. It has 567 ft/lbs as it comes; 580-600 might not be too hard.

marky mark

JD & Glen, thanks for the responses. Both of you offer valid points to consider. It would appear the alum rect port heads idea isn't the best way to go in my application. Thanks for the help!!!

Regards, Mark

Rolling Thunder

I'm with Glenn on this one. The ZZ502 is 9.6:1 compression has a 5800 redline, and unbelievable hp and torque curves (not much curve to it). Get the right exhaust (3") cooling, and gears and it'll keep you grinnin' for a long time. I'm in the process of topping mine off with digital sequential fuel injection which can't hurt its manners any.

Good Luck,
Dave

Glensgages

I was gonna go this route (shave the heads for higher CR, etc.) to replace the 'tired' 355" in my 12-second Z28.....until a buddy came upon a 433" BBC he'd built for a customer. After just 6 runs, the buyer said "No way, Jose!!!". My buddy bought it & sold it to me for less than HALF the cost of the ZZ502.
Steel crank, L88 rods, 11:1 forged pistons, big DART aluminum heads & intake, etc. At close to 580 HP (dyno-tested), it'd be WAY too-much for my 28" x 10" Goodyear Eagles, so we're pulling the roller cam valve-train out, & sliding a solid-tappet stick in there. It should run VERY EASY high-11s @ 110+..... :steering:
(Emmit Brown, scientist from "Back-to-the-Future" movie, voice:)
"Marty,...when this thing hits 88 MPH,.......you're gonna see some SERIOUS poopie!!!"

Guru_4_hire

I have been thinking about this myself

Why not look at the ZZ502 -- it comes complete with carb, intake, distributer and everything you need to drop it in and go for 7300 bucks assembled http://www.sdpc2000.com/cart.asp?act...id=120&pid=688

the 502HO would make a cool blower motor.

marky mark

The ZZ502 is what I refer to in # 1 example. However, for my application I can't use that intake due to hood clearance issue. My version of the ZZ502 would be with the listed intake and Quadrajet.

Only way I can use a Holley is to go the LS-6 intake route and rectangular port heads (assuming the Torker 2 is not a viable solution). That is why I asked about the rectangular port head choices.

Regards, Mark

marky mark

JDPatrick,

What rear gear and tranny combo are you running? Which carb also?

Regards, Mark

jpatrick636

I am running a Richmond 5 speed which has a 3.28 first gear and a a 3.08 rear gear. That works out to 10.1 to 1. Even with over 400 ft lb @ 2500 rpm the gear sometimes makes the difference (Viper's and Z-06's). However, in your case with the M-20 you have to choose between having it down low or a comfortable highway cruise. My last Vette had a built 454 with an M-20 and I changed from a 3.23 to a 3.73 and was very satisfied with both performance and drivability but I never drive on the freeway. You can do a lot more for the money with gears than you can with horsepower.

I am currently running a Holley 750 DP. I had an 850 on it but after the switch only 1 ft lb and 2 hp were lost. The idle improved and the throttle response is pshycic. However, at the time I had a true 2-1/2" duel exhast with cats which was choking the motor to the tune of 70 hp. Now that I have a custom 3" with H pipe and Spintech mufflers, I am thinking of going to an 825 Mighty Demon but have not done the research to see if it would be worth while. All of the research I have done indicates that the only sustantial gain will be at points over 5500 rpm. How much time does one spend in that rpm range? I will say that if every day drivability is your priority, stick with the 750, especially if you keep your current gears.

Good luck and keep us posted.

427Hotrod

Lots of ways to go hear. One would be to replicate my last 427 setup. Rebuild your current 427 with some 11.0 pistons (end up with REAL 10.5 or so) and get a set of Merlin or GM oval ports and have them ported by someone who knows them well. Install a street roller cam in the 240*/ .600 lift range. You could use the L36 stuff especially if you did some port work on the intake. I used a single plane and large carb, but you would still be OK. This combo could easily run low-mid 12's with traction and your gearing. IF you went to the next step and installed a Richmond 5 speed you could run high 11's.

This setup will run very strong with the 5 speed. I suggest this method since you could save enough $$ to afford the trans. IF you don't port the heads or run a smaller cam, it will likely maybe get into 12's at best. Maybe. The 427 is a great setup, but you have to build it right. Realistically, you could build your L-36 with some port work to stock heads, a little more compression and a real cam to easily get sideways in second gear and also run 12's. No big deal.

The 502 combos will run killer too, but your self imposed exhaust restrictions will really limit it. Those headers and 2.5" pipes are not going to make the 502 happy and gains above 4000 rpm will be drastically reduced and could easily be right back where a freer breathing 427 could spank it! Trust me.. my last 427 just loved jumping on Vipers at a 50 mph roll! Never had an issue!

If you stay with your current gears, I'd probably still run the oval port heads on it, but once again, at least some port cleanup is really needed. I think you could step cam up again to the same general specs as I suggested before and still maintain good vaccum. The Comp street roller I used last held 14" of vaccum and would lug to 1000 rpm in high gear with 3.36's with no issue, yet pull 7000 rpm if needed.

I know you're worried about header fitment, but I would also SERIOUSLY look at other heads. WA2FST recently installed a set of the new AFR heads on his 454 and he said there were no header issues. Those heads are arguably the best thing out there right now and will run circles around any of those other choices. The advantage of a good head is it doesn't require as much cam to run well, but if you do up the cam...it also responds well to that too.

A 502 shortblock, with AFR 305 (or even better the 315 cc CNC ones) a nice little street roller cam, the LS-6 intake and a 950 HP Holley (recommended it to WA2FST and he loves it!) could easily make 600 hp on pump gas. The intake would really hurt it, but the better other parts would help offset the loss.

Plus at least some 2" headers and 3" exhaust would have you in for a real ride for the same $$. You can still keep reasonable sound levels with big pipes. Find someone else to sell your current system to.

In the 502, the 5 speed would be nice, but not as necessary.


Good luck!


JIM

A C

Why not go with the shorty 69 L-88 hood? I know it didn't come on your car, but it was available on 69's, so it wouldn't look out of place. You would have a lot more carb/intake options.

OatBoy

my thoughts exactly

GDaina

the 502 will need 2.125" tube headers....remember, the function of the headers is to scavange the exhuast gases as fast as possible, and anything less than 2.125" exhaust on a 502, you will be choking the motor...I'm running 533 cubes, bought a 502 bare block, internal balanced 4.25" stroke crank, Eagle H beam rods, that are stronger and lighter than the i beam. By going with an internal balanced crank I was able to use my 427 harmonic balancer and flywheel...the price difference between a 4", 4.25" stroke crank is 0, same price. I'm using the street roller that 427 mentioned, and a Doug Nash 5 speed, 3.55 gears...square port aluminum heads, stock 427 hood, and my original tri power. Yea, I know, I could gain more hp by going with a Holley 4160, but, hey, I'm pulling 7k r's all day long, and I'm a happy man. Forgot, am running 2.125" inch pipes

marky mark

Wow, that's alot of info to take in. Thanks to all who responded!

I didn't think about the need to increase the exhaust system with the 502. I was more worried about the intake concerns, DOHH!!!

That really helps to hear all this first hand info from everyone.

One other question on exhaust: Would the set-up I mentioned in the first post here be acceptable for a 454???

Thanks to evryone. I do appreciate the input!

Regards, Mark :flag :chevy

mrvette

If you want to actually drive the thing around Jax Fl. you will want a 30% overdrive, and I would go DPFI closed loop, no matter which engine...
also I"d find a freaking way to get some real exhaust under there, even to modding the cross member get Rickey here in OP to help, or maybe his folks down in Middleburg....

GENE

MassVette

I'm using the 454HO in my '67(425 hp-500 lb torque). It's fairly mild-mannered, runs beautifully, has the mechanical fuel pump boss, and it works VERY well with the stock manifolds and side pipes. The ZZ/502 in the '79 is another story.
BTW, on the Gen V & VI BB's, you can't use the Mark IV heads, and the header flanges need to be recontoured for the ALUMUNUM Gen V & VI heads because of the head bolt bosses. Also, you need to get a clutch cross-shaft pivot bracket- available from Scoggins-Dickey Chevrolet (or fab your own).
Good Luck!
:yesnod: :chevy :chevy :yesnod:

GDaina

That's not quite true, Mark IV heads will bolt to the GEN VI block without any problems, it's the Gen V block that you have to use Gen V heads.

I am using the 077 D port Mark IV Aluminum heads, not interfearance of any kind with head bolts, or problems with exhaust flanges, though I did have to trim the bottom to clear some, but I thought that was because I'm using studs. Again, not a big deal to trim the bottom of the flanges.....a small hand held grinder does the job quick.

WPEDirect

Whutcha gonna do with yer 427...?

:blueangel:

MassVette

George- I believe the problem is with the water passages............