air or fuel, what am i running out of

[rigger3006]

just got 360 running,284/484 cam, ld340, 670 avenger, ported 302s with 901 springs,20 initial 34 total.i can take it to 6000 in 1st easy enough, but in 2nd it hits the wall at 5400. is this the 302s not having enough flow, or maybe not enough fuel ?

 

[MOPAROFFICIAL]

just got 360 running,284/484 cam, ld340, 670 avenger, ported 302s with 901 springs,20 initial 34 total.i can take it to 6000 in 1st easy enough, but in 2nd it hits the wall at 5400. is this the 302s not having enough flow, or maybe not enough fuel ?

I have found those avenger carb to be on the lean side, air bleed wise. Head flow, cfm wise , is not the problem, I can tell you that right now. Whats the port volume and has it been increased? Are you running a decent gear out back? That old 2.76 gear with a 280 degree cam bit strikes again.

 

[jos51700]

Get into where it peters out, hold there for a second or two, kill the ignition and pop into neutral at the same time.

Coast to a stop, pull a spark plug or two, and you should know pretty quick.

Could be ignition breaking up under load too.

 

[rigger3006]

355s, 3000 hughes tc, opened up ports myself as far as i dared and gasket matched to intake. ignition sounds ok. no bog whatsoever, nice smooth pull from 2000 to 6000 in 1st, cam behaves totally different compared to the 318 it was in before, maybe i'll ''borrow'' 750 quick fuel off wifes 340 see if theres any difference. the avenger still has factory jetting, havent got that far into it yet.

 

[MOPAROFFICIAL]

Do you know if the secondaries are fully opening?

 

[T-N-T]

901 springs are borderline for that cam. They recommend a double spring for it. I wonder if this could be part of the problem.

 

[rigger3006]

had no problem spinning to 6700 in 2nd in 318, same cam and springs and cam. never knew about double spring recommendation, i thought 901s were good to about 490 lift. definitely full throttle

 

[MOPAROFFICIAL]

had no problem spinning to 6700 in 2nd in 318, same cam and springs and cam. never knew about double spring recommendation, i thought 901s were good to about 490 lift. definitely full throttle

That last post, I like to assume you have the seat psi around at least 120lbs, I hope...and to next thing i was thinking, was if this guy has quench...why such high timing?? Now then from that...I ask, what is the cranking cylinder psi in this 360?

 

[T-N-T]

had no problem spinning to 6700 in 2nd in 318, same cam and springs and cam. never knew about double spring recommendation, i thought 901s were good to about 490 lift. definitely full throttle

They are borderline pressure wise. That cam should have about 120# of seat pressure. They probably work pretty good but aren't ideal especially for 6700rpm.

The 901's have .490 is the rated max lift. They are rated at 101#'s of seat pressure at 1.65" and have a 353# spring rate.

Comp actually recommends them for their XE268 cam but their tech line recommends 120#'s of seat pressure for use over 6000rpm. For use over 6000rpm they recommended the same springs that their XE274 & PP280H(their version of a 280 purple shaft) cam would use which are 995 dual springs which have about a 125# seat load and a 402# spring rate or one of their beehive springs. The PP280cam has 280/287 degrees of duration with .474" of lift.

Did you check the installed height of the springs when you installed them?

I just thought I would mention it, but odds are your carb is lean at WOT. That is probably the most likely cause.

 

[rigger3006]

springs were installed by reputable mopar shop, cranking psi is 130 avg., i dont intend on revving past 6000 with this 360, i have six days before it gets put away for the winter(great white north), just wondering why im hitting the wall at 5400, yes it is probably lean at WOT

 

[MOPAROFFICIAL]

130psi is low for that cam.
Carb-Try a weaker secondary spring.
If you were to pull a valve spring and see grooving in the spring pad...you'd definitely know you were bouncing the springs.
I've had them so boarderline, when the motor was half warmed up it would rev up nice and make the tq....but after being normal temp would seem flat, spring bounce. You need the right amount of spring rate.

 

[70aarcuda]

just got 360 running,284/484 cam, ld340, 670 avenger, ported 302s with 901 springs,20 initial 34 total.i can take it to 6000 in 1st easy enough, but in 2nd it hits the wall at 5400. is this the 302s not having enough flow, or maybe not enough fuel ?

360 with 302 318 heads...and you wonder why it dies at 5400 rpm...LOL

ran that cam back in the 80s with stock 340 springs which a 901 spring is...did not have any problems spinning 6000 rpm...but then again........

 

[MOPAROFFICIAL]

He gets 6000 rpm in first, its not too lil port volume, though its defintely not enough for max hp.

 

[70aarcuda]

1 st gear multiplication will get the engine to 6000 rpm...it is went the engine comes under load in the higher gears does that lack of hp or air becomes apparent....
an engine is nothing but an air pump.......no air in no air out...

 

[MOPAROFFICIAL]

1 st gear multiplication will get the engine to 6000 rpm...it is went the engine comes under load in the higher gears does that lack of hp or air becomes apparent....
an engine is nothing but an air pump.......no air in no air out...

Yes I hear you...though he says he ported them and opened them up ;)
Maybe not enough gear!

 

[krazykuda]

I ran a 484-284 cam in my 68 340 with x-heads, stock dual plane-square bore intake, holley 650 DP, and could take it to 6500 easy - I had to let off to keep from over-revving....

 

[MOPAROFFICIAL]

355s, 3000 hughes tc, opened up ports myself as far as i dared and gasket matched to intake. ignition sounds ok. no bog whatsoever, nice smooth pull from 2000 to 6000 in 1st, cam behaves totally different compared to the 318 it was in before, maybe i'll ''borrow'' 750 quick fuel off wifes 340 see if theres any difference. the avenger still has factory jetting, havent got that far into it yet.

I have no doubt the 750 makes more power and works excellent on this motor, the signals huge. Between the two, the 750 will give a very noticeable power increase above 4800 rpm.

 

[RAMM]

360 with 302 318 heads...and you wonder why it dies at 5400 rpm...LOL.

Winner, winner chicken dinner. My lawnmower engine will rev to 6k when I yank on the governor arm--doesn't cut worth a **** like that though. The heads and cam -basically the combo is far from ideal. Junk those 302 heads--I really wish Dulcich had never published that article-302 heads are garbage. Bolt an EQ Magnum casting on there and you will instantly regret spending even one second/one dime on those 302's. With 130 cranking compression install a Comp 262H and marvel at the 50-60 ft/lbs of torque you just picked up. NO amount of carb and ignition tuning/swapping will make a difference. My honest opinions. J.Rob

 

[MOPAROFFICIAL]

I'm concluding with this thought and experience.
5 years ago you could get bucks for those heads. I myself knew better, but people got into velocity and sold on mileage and torque...but the amount of material removed to get these heads near a decent port volume for the cid rpm range was beyond what novice porters are capable of..124 cc to 150cc 'near magnums' is a lot of work for hobby shop guys.I had a guy come to me with limited parts and best of both worlds thinking ask me to build something out of the limited selection of parts and money he had...so I stretched a '72 4 ear truck 318 block I had laying around to 4.040 and used 273 heads, closed chambers w/1.88 valves, 132cc runners flowing with a stock 974 head and peaking @215int/150exh [email protected] was a solid .470 lift 262dur 110 cl, 600 holley, performer carb with 323 gears its peak hp rpm was around 5600 and made a real 305 hp 380ft lbs. I basically made a redesigned 340 that makes more torque, last I heard he has over 4k miles on it and drives it daily.
To the op, as one of my first concerns -the port volume, its really lite for that stroke, if you want to get 6k in 2nd ...you can with more gears...but its not going to make a lick up there.
Tune the car for lower rpms or get new heads, you probably make great torque off the line I bet.

 

[Max1196]

Do you have a fuel pressure gauge in the system that you can monitor while driving? Smaller engine was good with the small fuel line system from the tank onwards forward, But an engine that has a higher demand for fuel will put a strain on the ability of the delivery system! If you have a drop in fuel pressure in second gear there is either a restriction or an inadequate system.

 

[rigger3006]

fuel system is 3/8 from tank to carb.only reason 302s are on engine is the 360 was from a motorhome and had 318 industrial heads on it,that is why 302s are on this motor. yes, i regret spending 1400 getting these heads built, shop guy even tried to talk me into a cheaper set of aluminum ones.doh! ive got 2 sets of j heads and a set of 308s, one of these will be my winter project,havent decided yet,

 

[MOPAROFFICIAL]

I easily get 265 cfm @.500 lift with the 308 heads. Use them.

 

[T-N-T]

I easily get 265 cfm @.500 lift with the 308 heads. Use them.

What do you classify as "easily"??? Is it having larger valves with smaller stems installed along with guide work and fully porting the head. Are you achieving 185cfm or more on the exhaust side at the same time? How many hours are spent doing the port work? What port volumes were achieved?

Since you say "easily" I'm sure that means there must be a good amount of flow increase left to be had if you tried harder....

Post up your number from the flow bench you used and which bench it was.

 

[MOPAROFFICIAL]

What do you classify as "easily"??? Is it having larger valves with smaller stems installed along with guide work and fully porting the head. Are you achieving 185cfm or more on the exhaust side at the same time? How many hours are spent doing the port work? What port volumes were achieved?

Since you say "easily" I'm sure that means there must be a good amount of flow increase left to be had if you tried harder....

Post up your number from the flow bench you used and which bench it was.

Whoa ...look at you, did I somehow offend you? 3/8 2.02 valves and "easily" comes from having a flow bench. I have done so many factory 340/360 heads that I can hit 245-250cfm Damn near blind folded..not really, but you get the sarcasm I hope.
I believe this thread IS NOT about what I can do or what you want me explain or prove to you. PM me next time or start a thread and call me out.

 

[T-N-T]

Whoa ...look at you, did I somehow offend you? 3/8 2.02 valves and "easily" comes from having a flow bench. I have done so many factory 340/360 heads that I can hit 245-250cfm Damn near blind folded..not really, but you get the sarcasm I hope.
I believe this thread IS NOT about what I can do or what you want me explain or prove to you. PM me next time or start a thread and call me out.

Easily suggests simple bowl work and port matching. Extensive would be an accurate description of what is required to reach your numbers.

You even stated in your earlier posts that

"tune the car for lower rpms or get new heads"..
And "I'm concluding with this thought and experience.
5 years ago you could get bucks for those heads. I myself knew better, but people got into velocity and sold on mileage and torque"
along with "To the op, as one of my first concerns -the port volume, its really lite for that stroke"

I must have missed the sarcasm in the post you made below....

I easily get 265 cfm @.500 lift with the 308 heads. Use them.

I was just wondering how you easily get 265cfm out of the intake side when others show the extensive port work required to hit 245cfm?

Shadydell is a good example. Shady Dell Speed Shop His numbers seem more inline with the reality I've seen first hand. The links pictures show it's not easily done also.


Your input on 302 heads sure seems to change in the different posts you've made. How is this any help for the OP??? Your advise is all over the place.