My 340 has slowed down,need help!

[torredcuda]

Ok,I`m not giving up on it tuning yet but it seems my engine has slowed down/lost power since upping the cam and porting the heads-I should be going faster!Once I exhaust all carb tuning and such and barring something is wrong with it-I`ll do a compression and leakdown test- I need to figure out where I went wrong and what I need to change to get my car back to running low 13`s or hopefully high 12`s.Here is my combo and what I changed last year.

`72 340 .030 over
forged TRW 10.5-1 (rated?) pistons,
steel crank,stock rods,all balanced
"J" heads with 2.02 intake/1.60 exhaust, fully ported by a local guy who does lots of local racers stuff and knows what he`s doing,no flow numbers though
Mopar .508/292 cam,recommended by porter
Edelbrock Torker
Holley 750 DP with Proform main body,still working on jets,squirters etc.
Mopar electronic ign,orange box(need to upgrade)Msd coil,running 17 degrees initial and 37 total in around 2000rpm

hooked into a 4 spd with 3.91 rear
car weighs around 3500,set up for cornering not drags with big block torsion bars and leafs,gas shocks
runs on regular BFG`s,full exhaust

This car ran a best of 13.26/102 with an 727 auto,.480/292 Elgin cam,Holley 650DP
I swapped to a four speed and lost a few tenths due to not power shifting all the gears as I have no rev limiter
I then ported the heads and swapped cam/springs last year only to find my 650 was worn out so now I have a good carb but could only manage a 14.3 last week.The engine pulls good up to 6500 but seems lacking somwhere.

The only unknown is true compression ratio as I know the TRW pistons are not true 10.5-1
The heads have been cut at least .010 but not sure on the block

Where did I go wrong?Should I be running better or is it just tuning the new combo?
I may pull the motor this winter to check it out and do whatever I have to get my 12 second quarter!
Any suggestions?

[360 'CUDA]

Of course keep tuning it...
Two things come to mind

Cam timing and bent exhaust valves
Did you check the valve to piston clearence?
Sometimes on those 340s you install the cam at the recommended advance the exhaust valves start touching the pistons bending them. Then the valves head breaks off and vaporizes the piston.
I woud do that compression test soon.

[Chryco Psycho]

Head porting is ambiguous at best , it is very easy to actually hurt power , a friend had a 340 that would not even run stock ets , we tried everything to improve power but nothing worked , i believe the heads were badly ported , I am also not a big fan of the 509 cam , it has a lot of duration , not a lot of lift & may be hurting power also 

[Cuda72]

I don't mean to steal this post, but I have almost the exact same setup on my '72 Cuda (MP 280/.470" grind though) and I'm curious how the Comp Cams XE268 would do in this setup? I'm running a 3.55 gear out back and my best ET is 13.9 @101mph (with NO traction).

- Cuda72

[Chryco Psycho]

C9mp doesn`t make a great cam for a Mopar , most grinds are designed for Chev & ground onto Mopar blanks ,
 I use mopar , Engle or Lunati/UltraDyne grinds in Mopars

[torredcuda]

CP,that is kinda what I was afraid of as the car will pull past 6800 but doesn`t seem to get there very fast so the porting is too much and hurting performance on the bottom.I really liked the long duration 292/.480 cam before I ported the heads so I figured it was the porting not the cam upgrade.So I will most likely pull the heads-should I use ther truck heads or go for Eddys?If I also swap the cam what do you recommend that will get me in the high 12`s?I do street drive a lot but don`t mind the rough idle.

[Chryco Psycho]

I know the truck heads are good for 41 HP , I have not tried the eddys but just looking at them I feel the truck heads are at least as good & will save you some $$ as well
 do you want a solid or hyd cam ?

[ntstlgl1970]

Can you post the mph for the slower run and your 60 ft times? And am I reading right you went from a 650 carb to a 750 now?

[torredcuda]

I`ve only run hyd cams but either is fine.What will I need to do to the truck heads-bowl clean up,springs,rockers?
I went from the .480/292,650 and stock J heads with 2.02/1.60valves to the .508/292,750 and ported heads.I went from 2.0`s to 2.2-2.3 60 ft and down from 98-100 to 94-95 mph.

[matt63]

C9mp doesn`t make a great cam for a Mopar , most grinds are designed for Chev & ground onto Mopar blanks ,
 I use mopar , Engle or Lunati/UltraDyne grinds in Mopars

I thought that the Comp Cams XE grinds were a "modern" fast acting cam versus the MP old technology?

[ntstlgl1970]

Have you tried running it again with the 650? And is your fuel pressure/timing/advance all good? You changed a lot of things all at the same time......

[Chryco Psycho]

I thought that the Comp Cams XE grinds were a "modern" fast acting cam versus the MP old technology?

My experience shows other cam grinds still work better

[torredcuda]

OK,so what cam do you suggest to get my car into the 12`s?

[Grancoupe]

How much time do you have into tuning this thing? I was able to bring my car form low 14's to 12.5's just by setting the carb and timing. It took three visits to the track and a whole lot of passes but I think I'm squeezing out quite a bit from the motor now.

[Chryco Psycho]

are you looking for a solid or hyd cam , what RPM range , auto or standard ?