Without getting into the specifics of your clearance or lack there-of (I think you'll be fine, with decent compression to boot), I'll comment on your overal build:

Need more cam for the head flow you've got, and you need more carb.

As it sits, it should be a good safe mid/perhaps low 13 second car...provided you have good spark/timing.

However, at first I'm a little disappointed in the flow of the "worked" heads...if it's minor work, then that's good...but if they were going through and porting the crap out of them, then I at least hope that it was on a VERY pessimistic bench. With that cam, I think you would have wanted flow in the 270-280 cfm range. With the flow you've got, I'd want at a minimum the next step up, but likely something in the 240 @ .050, .530+ lift range...or better yet, a roller cam with similar duration @ .050 as your current cam.

Also I'd want probably a good Holley 700-750 DP for the best performance at the track.

All in all, as it sits, it's a great street-strip combo, no doubt.

Here is the numbers I used:
Block Deck Height = 9.600"
Bore = 4.070" (0.030 over)
Stroke = 3.310"
Rod Length = 6.123"
Piston Height = 1.840" (TRW 2316)
Valve relief volume = 7.5cc (seems big, is this right?)
Est. Head Gasket Volume (0.040" thick) = 9cc
Cylinder Head Volume = 75cc

If the engine is the stock 9.60" deck height the piston should only be 0.018" above the deck, and the compression ratio calculates to 9.05:1

If the decks have been milled 0.012 to where the piston is 0.030" above deck, the compression calculates to 9.29:1

If you use a 0.020" head gasket (estimate 4.5cc) or mill the heads 0.020" the compression should be approximatly 9.76:1

I don't think the positive piston height will be a problem, but check the head chamber height to be sure. On my 360 heads the chamber was recessed 0.070"+.

The combination looks good for a dual purpose vehicle, but most likely mid to high 13's?
I don't know the cars weight, and the track altitude. Anyhow, to run 12's you will probbably need more cam and compression?

Actual compression of a stock 340 ('68-'71) is around 9.5:1.

It's a low 13's-high 12's combo if you can get it to hook. My car is similar with stock heads, less cam, and runs 102 in the 1/4.

The carb will be the choke point up top. Not near enough IMO.

Thanks everyone ... I've got two carbs to choose from in the garage - 670 or 770 Avengers. Cam I could probably exchange at Summit for next step up Lunati (?). 68 motor with forged crank, these pistons are forged as well, i was thinking ahead as I may spray with one sole (albeit childish)purpose in mind .... beat my buddies 93 Mustang Cobra which runs 12.8's or so. I've got a point to prove (I know - grow up your pushing 50 bro' !) Anyway all the help is appreciated. Heads were not worked extensively, I got about what I paid for - I guess.

I believe I would step up to the 770 - or sell both for a double-pumper ! Cam - I won't suggest, if Summit will let you exchange, you'll be limited to a stock grind (which is fine for your purpose). I'd wait for others to suggest a cam ..... As far as the childish issue of wanting to one-up your buddy - isn't that what makes us tick in the first place ?

I think the 670 will be enough carb but no reason not to try the 770 if you have it also.

The cam is enough for a good low 13 second car. If you want low 12s you will need more gear and cm.

You have plenty of Cam,and use the 770...its way better to lean out a bigger carb than richen up a small one. My '72 Demon had a stock bottom end 360 w/MP .484/284 Cam,Holley strip dom intake,and Holley 750,3800 stall, 4:56 gear,SS springs,9x28 slicks and ran a best of 12.28 @ 108 mph. Now I did race it every weekend,so I had a lot of time to fine tune it.
Sounds like you want to be a little more streetable,so don't go crazy with the gear,3:91 sounds good,and don't be afraid to run SS springs on the street,they'll be just fine. You should be able to dip into the 12's no problem!
I don't like the way your machinist sounds,you're paying him good money for hopefully a good finished product,Don't be afraid to get info out of him.
I hope it all turns out well in the end!!
Best of luck!!
Wally.

The MP 484 cam is a bigger cam than that voodoo "268" cam by a healthy amount...even if it doesn't have the lift the the voodoo has.

241 @ .050 w/ 108 LSA for the MP vs 226 w/ 110 LSA for the voodoo...

The "voodoo" series has two cams in it's line-up, both available from summit that could do the job nicely...both MIGHT hit your goals, one certainly will.

The 60404 features 234/242 @ .050, .513/.533 lift, 110 LSA...with the mild porting, this cam stands a good chance of getting your ET goals provided the chassis is up to snuff...should be fine with your torque converter. With the aggressive ramps, it's should be comparable to the MP 284/484 cam in terms of power, but with better vacuum/idle, wider power band.

The 60405 will DEFINITELY get your goal (and perhaps more) and should have comparable if slightly better vacuum and idle to the MP 284/484 cam; but it'll make a healthy bit more power...specs are similar at 241/252 @ .050 on the split pattern cam, but with a wider 110 degree LSA (overlap is still greater due to the large exhaust duration vs the single pattern MP unit). Where this cam shines over the MP though is it's ramps...very aggressive (not the most aggressive; racer brown and hughes offer better...but the voodoo is probably the best you can exchange for at summit) featuring .533/.552. It's lift @ .300/.35/.400/.450 should all be significantly better than the MP unit as well...making the cam seem bigger w/o the all the poor idle/driveability of the MUCH bigger cams.

The caveat is, what springs are you running and are they suitable for either cam?

I would leave the combo alone and spray it with a 150 shot. If you go swapping to a bigger cam now your going to need more head work, More compression, More gearing, different valve springs, ect.


You have a real nice, strong street car right now.

Valve springs installed -

Part Number: CCA-930-1
Number of Springs Per Valve: Dual
Outside Diameter of Outer Spring (in): 1.550 in.
Coil Bind Height (in): 1.160 in.
Damper Spring Included: Yes
Spring Rate (lbs/in): 354 lbs./in.
Inside Diameter of Outer Spring (in): 1.150 in.
Inside Diameter of Inner Spring (in): 0.795 in.
Valve Spring Style: Standard

AdamR - I'm leaning towards your suggestion - I need to run low 12's maybe a hlf dozen times, with nitrous is fine if that'll be my best chance (no shame here as the Mustang sprays as well)Already running superstock springs - 3/4 relocation kit so I'm thinking on that fatefull weekend I'll borrow the rear slicks/wheels (have a source) switch rear gear (find a used set) and use the nitrous. I beleive I could get a few low 12 runs if all plays out in my favor. After I've proven my childish point - my life can go on (set car back up for street/cruise-ins) Sound good? Also - I will have a few trips to the track to dial in before our grudge match.

With the juice you wont need anymore gear. 391s will work.

Just curious, why did you use Comp springs with the Lunati cam?
Those springs have a 1.900" installed height.
The recommended springs are Lunati P/N 73949. Their installed height is 1.650".

These are what the shop installed - I told them what cam I was planning on using, they said these Comp springs would be fine - charged me 90.00 parts/(mostly)labor,. Should I change 'em out ?

Since the stock installed height is MUCH shorter than 1.9" I would investigate this further. The Voodoo hyd cams are designed by a friend of mine,I'd go solid lifter cam or PM me for more info.

This article talks about retainers to raise the install height:

http://www.compcams.com/Community/Articles/Details.asp?ID=-738676943

OK?