318, made changes, no gain?

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Nice Glass

Nice Glass

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Riddle me this Batman...

I have a '65 Barracuda with a mild 318.
- 9.0:1 Flatheads
- Mopar Perf 484 cam
- 360 heads
- Thorley Headers
- 3.23 gears

I ran 14.30's-14.40's fairly consistent last year with this set-up. Changed gears to 3.91 and went from 22" to 26" tires for the 1st race this year, really no change. (Pulled a 14.09 but weather was awesome, adj. altitude was 578 ft.)

Changed out the tranny (was running the original in it yet) it's from a '68, still a 904 but with a taller 1st gear, Griner manual valve body (works awesome and sharp) and a 4000 stall converter. I ran anywhere from a 14.60 to a 14.90?!? (Adj. Alt was between 1800 & 2300 ft)

Question here is, is it just too much converter for the motor.
Is there a way to build this a little more consistent, I seem to get wild numbers out of it sometime. What should I be looking for that can throw a really slow number in there or why it will progressively fall off during the day.

What can I change here to get a nice mid-13, solid Sportman class car?

I'm not looking for crazy fast here, just the best, least expensive way of fixing the problems and putting me into the class I want to run.

Thanks!
KC
 
while increasing the rear tire size by 4" in diameter you basically negated the change in the rear gearing..

leaf springs??? rear shocks???

cylinder heads??? 318 heads?....valve springs???

MP484 cam is alot of duration for 318....but the converter should have helped it out...

wild numbers out it sometimes????? spinning tires???

what carb..? How is the distributor curved?
 
Nice Glass said:
Riddle me this Batman...

I have a '65 Barracuda with a mild 318.
- 9.0:1 Flatheads
- Mopar Perf 484 cam
- 360 heads
- Thorley Headers
- 3.23 gears

I ran 14.30's-14.40's fairly consistent last year with this set-up. Changed gears to 3.91 and went from 22" to 26" tires for the 1st race this year, really no change. (Pulled a 14.09 but weather was awesome, adj. altitude was 578 ft.)

Changed out the tranny (was running the original in it yet) it's from a '68, still a 904 but with a taller 1st gear, Griner manual valve body (works awesome and sharp) and a 4000 stall converter. I ran anywhere from a 14.60 to a 14.90?!? (Adj. Alt was between 1800 & 2300 ft)

Question here is, is it just too much converter for the motor.
Is there a way to build this a little more consistent, I seem to get wild numbers out of it sometime. What should I be looking for that can throw a really slow number in there or why it will progressively fall off during the day.

What can I change here to get a nice mid-13, solid Sportman class car?

I'm not looking for crazy fast here, just the best, least expensive way of fixing the problems and putting me into the class I want to run.

Thanks!
KC
Click to expand...
first why did you go from a 22'' tire to a 26" tall the taller tire will take some of the gear away with the smaller tire that might make the 3:91 run like its in the low 4:00.s give or take a little there is a way to work out how much it well change the big thing is you'd idealy want your tach reading about 300 rpm under make for hp rating not over the cam max hp at what what ever they say it is ( if the cam makes say 300hp at 6000 rpm you should cross the finish line at about 5700/5900 so you motor is still making max hp not droping hp
also you know going to the 369 heads on the 318 you will drop the compression the combustion chambers on the 360 heads are bigger so a loss in compression
 
leaf springs??? rear shocks??? - leaf springs

cylinder heads??? 318 heads?....valve springs??? 360 heads, stock

MP484 cam is alot of duration for 318....but the converter should have helped it out...

wild numbers out it sometimes????? spinning tires??? -no spin, i never spin

what carb..? How is the distributor curved? -600 Edlebrock, FBO distributor, they did the set-up...
Click to expand...

see answers above...
 
Yeah, tires size is a big difference. plus bigger tires is more weight to carry I can have a 26 inch tire on the back of my truck and run 16.0 @84 and now I have 31 on the back and I run like a 20 flat huge difference.
 
ok...you got 360 heads....what valve springs..?

if the car is launching at 4000 rpm....is the engine laboring to acelerate???
 
70aarcuda said:
ok...you got 360 heads....what valve springs..?

if the car is launching at 4000 rpm....is the engine laboring to acelerate???
Click to expand...

Valve Springs are stock.

Was recommended that launch RPM should be between 1600 to 1800, Hubby actually brought it as high as 2000. Flash over was expected to be around 3800, I honestly don't know where it occurred. I launch off of idle without a difference in our 60 fts though. Another puzzle/concern...

It didn't seem to have any problem with aceleration, it felt good. 60 fts were slow though, last one was 2.24. It's snapping through the burn outs better than it ever has too.
 
A clarification on this motor, we didn't build the engine, it was purchased this way. I was running decent numbers with it last year, I actually took 2nd in Street Trophy 2 years in a row.

I wanted to bump classes, just to Sportsman, deeper gearing seemed logical, new tranny was a must.

I will try to answer questions on the motor as you ask them. Some of them I just may not have...
 
I see a few things. First, the engine. As was stated a 318 with 360 heads is not 9:1 unless the machinist was really saavy. So what I think you have is "9:1" pistons but with heads that reduce that to closer to 8:1. Then that MP cam... It's way too large for that combo. If you want to verify what you have quickly, get a compression gage and take readings from the engine... Running temp, pull all the plugs, and block the throttle wide open. If it's less than 140psi that's what you have. Then there's the stock valve springs. They should be tossed in the dumpster and replaced with a performance spring, and if you have the odd exhaust valve rotator type retainers, toss them too (8 on exh valves). That cam cant make power if the valves are not controlled by the proper spring even if the rest of the combo IS matched. Lastly, the FBO ignition. You need to look at the paperwork or do some checking to see what the timing curve you have is. My guess is it might be close. But I've seen FBO be WAY off too. So it's worth it to make sure it's good enough and not worry about it.
Next the gearing. The gear change helped, but then you went to larger diameter tires. Larger diameter tires have a lot more tread contact patch than a smaller one. They also will effectively raise the rear gear ratio which as stated is exactly what you tried to change. 4" of diameter is about a full turn, so you went to 3.91s w/22" tire, and then lost a full turn, bringing the effective ratio up to 2.90s, and giving twice the contact patch. Thne you have the higher 1st gear taking more away.
You're left with a softer feeling lower end, and much less mechanical advantage with the rest of the setup. The convertor will only help if the engine is making power up that high.
I think it's a mismatch. To fix it quick, I'd replace the convertor with a cheap 10" 2500 stal, replace the gears with 4.10s, repalce the valve springs, and stick in a cam like the Comp XE262 to get the cylinder pressure back up. That should get you well into the 13s.
 
4.10 vs 3.90 isn't much, not for the cost of switching.

Cam and valve springs is needed, the converter might be ok. I had a 318 with .030 cast pistons and mp 360 heads milled .030. That motor I spun to 6,500 daily and flirted with 6,800 many times (3 years after the head swap my #3 rod bearing spun),

You might wanna get a custom cam--in fact I have a 2 year old custom cam grounded by Mike Jones in NC. It looks very nice and I have the matching lifters-or you could run new. I be posting some items in the for sale forums later this week. The cam is 220 @ .050 and 111 lbc has .465 lift with 1.5 rockers.
 
1)What carb are you running????
2)What was your mph?????
Your mph tells a lot about how your car is running.

The biggest problem you have is by far your 60 foot times.
3)Are you running slicks????????

For every tenth gained in your 60 foot,on average you gain 2 tenths on the other end of the track.
SO...If you can improve your 60 foot by,let's say 3 tenth's,it would be going over a half a second faster.
You should be running in the mid 13teen's.
Since you are running that .484 cam with a 4000 stall converter and also with 360 heads on a 318,there is only three things it could be that's killing your et.
NO SLICKS \\\ NO COMPRESSION \\\CARB IS SET UP WRONG
 
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