cams and reversion again....

[Rexx]

I did a search on the topic of reversion and cam specs. Unfortunately, I have not found a good answer to my particular situation.
My setup:
454 punched out to 467 CID
8.7:1 CR
750 CFM Holley
Dual Plane Weiand Stealth
Rect. Port Heads
Stock Cast exhaust manifolds
And the key...
Cam: 224 intake 224 exhaust at 0.050"
296 intake and 296 exhaust SAE
510 lift on exhaust and intake
117 lobe separation
Melling P/N 22219
My goal was to make 400 hp at 5200 RPM...thoughts on reversion?
I will be running in saltwater. Should I consider extending the inner tube of the risers and to what dimension if I do (if needed)?
And what would cause a pesky backfire? Excess fuel/poor carb adjustment? The HEI timing does not seem to cure it and unless I had a senior moment, I'm pretty sure I got the cam timing correct. What should the timing be for ignition at 800 RPM? What is the best method to set timing with the motors spinning on my garage floor and not under load in the boat? :confused:
Cam break-in on both motors done with oil pressure and water temps happy :rollside:
Thanks,
Tom
1989 Baja 320 Force

[cstraub]

No reversion.
Chris

[GofastRacer]

I don't see a problem with reversion but I think you need a good all around tune up!..

[Rexx]

Interesting....
The people in the business to sell marine parts said I had a problem with reversion with the cam being used and wanted to sell me $5000 worth of exhaust system to fix it. The shop who did the engine machine work said the cam they selected for the magic 400 hp would not cause reversion.
Does it sound like I'll get the magic 400 hp with my setup? Not looking for 500 hp...needs to be seaworthy!!! A broke motor is no good when you are stuck in the Atlantic 30 miles offshore. Why the backfiring?

[Jet City]

I wouldn't sweat the reversion issue, I also think you have tuning issues. I like to use an adjustable timing light (Sears), set full advance to 34-36 degrees, recurve distributor if not in by 3000 rpm or if initial is to high for decent starting. My guess is oval port heads would have been far better for your application.

[Rexx]

I've been told the same thing with the heads, only, the motor came with the heads and the intake..so I gots what I got without spending a whole lot of cash.
I'm starting to think the backfiring is fuel related. This is only happening on the second motor. Dial the timing retard or advance and it basically positions the flame/popping either in the flame arrestor or in the exhaust. The float bowls seem to actuate fine, so I'm not sure where the extra fuel is coming from. The other indication of excess fuel, I can smell it when I restart after it is warm. It fires up immediately when it is cold, but is hard starting when it is warm..another indication of excess fuel. The electric choke seems to work fine. So, is this just a carb adjustment? Can it cause that much fuel to go into the engine for backfiring? Or is it a few bad spark plugs (they are all new with just break in time on them).

[cjordan]

I ran a 252/258 @.050 .680/.708" 114CL SOLID ROLLER with Gils on a 502 in my Baja with never a hint of reversion.
You're fine.....especially with a 117CL, that thing must idle like a sewing machine :sleeping:

[1BIGJIM]

More info, is the backfire coming from the intake or exhaust? Did you get the valves adjusted properly? Does it backfire when you give it gas or all the time?
JIM

[Dave C]

thays some funny sh it right there, I dont' care who you are. :D
I'm with you on that one. I swear that one day I will hear a salesmen say.... "You know our new polished, plated exhaust system is the cure for all your ills, including cancer" ..... lmao. :idea:
Re: backfires, make sure the valves are set and sealed properly too.
Interesting....
The people in the business to sell marine parts said I had a problem with reversion with the cam being used and wanted to sell me $5000 worth of exhaust system to fix it.

[GofastRacer]

I'm not sure where the extra fuel is coming from. The other indication of excess fuel, I can smell it when I restart after it is warm. It fires up immediately when it is cold, but is hard starting when it is warm..another indication of excess fuel. The electric choke seems to work fine. So, is this just a carb adjustment? Can it cause that much fuel to go into the engine for backfiring? Or is it a few bad spark plugs (they are all new with just break in time on them).
You have an internal leak in the carb, when you shut it off it drools that's the reason for hard starting and smell after it's been running, check the metering blocks for warpage and the main body, the main body should be milled anyhow!. If it spits out the carb it's a lean condition, out the pipes it could be timing, plugs, jetting!. From your description of the situation, I'd start from scratch on the tuneup, may save a lot of headaches!..

[Rexx]

Well, I bought an adjustable timing light....should have had this thing in my tool box many years ago from all the motors I've worked on. :cool:
After setting the timing, I will go through the carb to see what is going on. Previously, the fuel would dump from the foward J vent tube during start. After playing with the float bowl (no obvious hangups), the fuel stopped dumping. As for the valve adjustment, I did the normal rotation of the pushrods and then an additional half turn on the nuts after the rods became stiff to rotate. It will idle, so I have a tough time believing the cam is off...but, guess it is still possible. It sucked down 5 gallons of fuel with about 30 minute of run time...so the extra fuel is coming from somewhere. My other motor only ran 2.5 gallons from a similar breakin. What would be warped in the carb? You can only take the bowls off and some screws...I'm unaware of a metering block...could someone make me aware?! :confused: These are 750 holleys. Maybe I should swap carbs with the other motor to isolate the problem to the carbs?? Isn't the whole purpose of an internal combustion engine to keep the combustion internal? Right now, I have the worlds first "external" combustion engine...flame either in the flame arrestor or in the exhaust by position of the distributor. :cry:
117 CL...that is probably the ticket for no reversion. Thanks for that info, adds some piece of mind. :cool:

[GofastRacer]

Sounds like the carbs needs attention big time, the metering blocks are between the bowl and the main body, it's time to rebuild them from scratch!...

[Rexx]

Where would I get a Holley rebuild kit?...Holley.com? :hammer2:

[GofastRacer]

Any local speed shop or Sumitt, Jeg's, PAW, just give them the List#!.. ;)

[Rexx]

My first set of big blocks.. :rollside:

[GofastRacer]

Cool!.. :cool:

[Jet City]

glad to hear you got the timing light, its an essential tool IMO. I'm just curious why your so concerned with reversion, I've run 110 LSA cams with log exhaust without any troubles, most marine grinds are in the 110-112 LSA range for N/A engines, did you ever get a recomendation from a cam company?

[Rexx]

nah..some company instilled the fear of God in me by stating I needed special exhaust for the cam I was running. Per this site and the shop who did the machine work, the cam does not seem to be a problem...dang backfiring though.........

[Rexx]

Got the motors into the boat...what a beeatch getting 454s suspended 13 feet in the air!! :jawdrop:
My brother was down here in S. FL for a few days, so I had to get the engines in while I had the chance. Final tune and resolving the backfire issue is now the next thing with them installed.

[WETTE VETTE]

I ran a 228/235 @ .050" hydraulic flat tappet Erson cam with stock Merc iron manifolds with no problems with reversion. The LSA was 112 and it was installed on a 108 intake CL. You should be just fine!!

[Rexx]

All responses seem consistent. Sounds like these guys were being sheisters and wanted to sell me an exhaust I didn't need. Should have known when the guy didn't even ask about lobe separation which seems equally important as duration.

[Havasu Hangin']

All responses seem consistent. Sounds like these guys were being sheisters and wanted to sell me an exhaust I didn't need. Should have known when the guy didn't even ask about lobe separation which seems equally important as duration.
I think it's actually the overlap that causes reversion (exhaust valve open while the piston is on the intake stroke for a slip second). Overlap (low LSA and long duration) are great for high RPM HP (scavanging), but not so good for low RPM reversion with wet exhausts.
LSA and duration are both factors in how much overlap a cam has.

[NAMarine]

Rexx, Where are you in S. FL.?

[Rexx]

uh..urr, overlap, yeah, that's what I meant :confused:
I'm in Hobe Sound. Can you align the engines with the input shaft with the yokes apart? OR do you need the special alignment tool?
Next thing...rebuild the outdrive :rollside:

[NAMarine]

Rexx, I am in Jupiter farms, dude. I have the alignment tool for the merc if you need it and since you are on here. I also have someone that does all my merc drive rebuilding if you want. Just give me a call 561-748-4519. My name is Geo(Joe)..

[Havasu Hangin']

uh..urr, overlap, yeah, that's what I meant
Yeah, that's what you said...I guess I just repeated it. My last (and current) motors have a bit of overlap (236 with 112 LSA) and still no reversion with Gil or EMI exhausts.
224 with 117 LSA is a very conservative cam. Did they dyno the motor with the stock wet manifolds?
Stock cast manifolds need to be rinsed very well in salt water, or you may get reversion no matter what cam you put in. :supp: Most guys switch to aftermarket exhausts for the corrosion resistance and better flow.

[Rexx]

Cool...give ya a buzz after I trow down some chow.
Judging by the condition of the palm trees, I should have known you were a local. If the palm trees are happy, so am I!! :)

[Rexx]

I kinda fibbed about the cam :squiggle: ...the lobe centers are 114 intake and 117 exhaust. Please tell me this cam is better than stock!!! Dang it, I want my 400 hp!! :cry:

[don johnson]

I am running 670 lift, 266 intake, 272 exhaust, 114 lobe centers in both my Teague blower motors with Imco Powerflow Plus. No reversion what so ever.

[Tahiti350]

On the backfire problem, I recently changed intakes (SBC) and now I get a similar popping out the carb when I tip in the secondaries. Never had a problem with the Torquer, now have a Performer RPM. Running a marine Edelbrock AFB. Does this carb use a separate float for the secondaries, or do I have other problems? Didn't mess with the valves, and the timing is the same as before (have tried advancing and retarding from baseline with no difference).
GaryB> Tahiti350