cam/converter selection

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Rapid Robert

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63 dart stock car. 360 2bbl 3.73 rear 904 trans 9-1 cr. 3/8 mile high banked dirt track. next engine build, on hand I have a new converter specs say 4000-4500 stall (advertized?) and a howards hyd cam 71841-09 specs say rpm range 2300-6000 intake duration at 050 is 235 ex dur is 243. advertized dur is 289 intake/297 exhaust. intake lift .488 ex is .480" lobe seperation is 109. do these sound like good choices or should I see if I can exchange em for another cam/tq if the companies will allow that? thank you for your time. RR
 
watching. does the car run in second gear most of the time? it "seems" like the duration could be more because of the rpm range but the compression may need less duration. and that is why I am watching and learning. Thanks for letting me butt in. Bob
SP or DP intake, 2 or 4-barrel carb?
 
Something’s not right, 3/8 dirt we always ran 5.83-6.20 final, 3.73 direct wouldn’t get you to 5000.
3.73 in second should get you in the 5.5 final range, 15” rubber I take?
 
I have not raced Circle track since the 1960's,
but that seem like a pretty loose converter for
that application and might build up a lot of heat
for the transmission to deal with in that application.
 
What heads are you running and are they and the intake ported?

Seems like alot of stall, what rpm does the torque peak?
 
Have you figured your dynamic compression with that cam?

You may have to increase the static compression ratio.
 
Agree with above, that converter is too loose for a roundy car, imo.
Have you run the car? What is your rpm, coming out of the corner? And what is your engine rpm at the end of the straight as you brake for the turn? That will tell you where you need to cam/converter for more performance.
 
is that 3gear in a 4speed ?I ran 2 gear in a 833od unit with a 1.67 second gear and 4.30 gear came in around 6200 rpm on the same 3\8 high bank track dirt ,the GM carb works well find one with the 1 3\8 venturi
 
good comprehensive info! much appreciated. the current eng was in a later dart & my racing buddy that does the driving (so far) wrecked it after several laps so I put that eng in the up & coming 63 dart. we tried to dyno it but it was too lean to do any WOT pulls & at that time I was not able to rejet it. the trans is a "regular" 904 running in third. I can call Howards & see if I can exchange/refund this unopened cam for one with 106 LSA & .050" more duration. yes I had read that the rear should be in the 5's & I have some 4.11's. I will call cope & see if I can exchange the converter (it's new) for a lower stall. & if not then send it in to someone to open it up when I find out where it needs to be at. CR limit is 9-1 static & I was very close to that. it is unported genuine EQ iron heads. I just bought a high dollar modified 2bbl & the venturis were the max allowed which was 1&3/8 iirc. dont have any info on the RPM coming out of the corner or RPM at the end of the straights but I have noted that & will find out and I will do a compression test. RR
 
IMO,
and I've never raced,
is that, if you are limited to a certain Static compression ratio, then to keep the Dynamic pressure up, you need to close the intake as soon as possible, working off the advertised numbers,( assuming they are in the .006/.008 tappet lift range).
This means a few things;
1) you need a cam with a fast rate of lift, and
2) it will need to be on a tight (small number) Lsa.
3) with as small a split pattern as possible

The cam in consideration is none of these..
However, I suppose that with a 4500 stall, this is not that big a deal.

To illustrate this,
Your selected cam; 289/297/109, installed at split overlap, will look like this; 289intake/108compression/101Power/297exh, with 75* o-lap, and 72* Ica
Most of that 75* overlap is gonna be sucked up in the ramps;
54 * of it is below .008, (Assuming the 050 spec is in fact .008) leaving just 21* as being useful.
The Wallace calculator predicts that the DCR will be 6.77, with pressure of 128.
On the street, these numbers would produce a very weak bottom end, and a markedly poor throttle response, compared to numbers over 185psi or even 165psi.

>Suppose we take the same 235 @050 intake spec, and combine it with a 239 exhaust lobe, but increase the intensity from 54* to 44*, and then tighten the LSA to 107*.. the new numbers, also at about split overlap, look like;
279 intake/114 compression/ 111Power/283exh, with 67 o-lap, and 66* Ica
Of the 67* overlap, now, only 44* goes to under .008, leaving 23* as useful. about same as before(21*).

Now, comparing the numbers, the new cam has;
plus 10* of Power extraction, and
Plus 6* of compression.
The Wallace calculator predicts that the DCR will rise from 6.77 to 7.0, and
the cranking cylinder pressure will rise from 128psi to 137psi
These are increases of 3.7%, and 7.0% respectively.............
From what is, essentially, the same 235*cam. and

>In other words, you could run a fast-rate cam, about 2 sizes bigger, than the current selection, to run the earlier pressure/lower Dcr numbers, For instance; lets add 14* (about 2 cam sizes) of fast-rate to 235 and 239.
equals 249 and 253 exhaust, then add back the 44* of clearance ramps, and lets tighten up the LSA another 1* to 106, and I get , again at split overlap;
293intake/108compression/105Power/297exh with 83* o-lap, and 72* Ica
NOW: Of the 83* overlap, 39 is now at over .008 tappet rise!
compare that to the selected cam at
289intake/108compression/101Power/297exh, with 75* o-lap, and 72* Ica
and still same 235*@.050

Compare the effective overlaps of 39* to 21*; that is 18*, which is, effectively, about 2.5 cam sizes. If you are running tuned headers, this is a very big deal.


The above is for illustration only. I know nothing about racing.
 
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I haven’t raced this type of class for 35+ years, but I do know some people currently racing imca in this general class. Most if not all are running a Chevy crate engine with a powerglide in high gear, theyrun a direct drive dummy converter so basically it is direct drive and they are running the same gears as I mentioned above depending on track shape. Mike Jones is a guru on these types of engines and maybe afew people on this site may get you in the right direction, not sure everyone who recommends a cam has knowledge of circle track requirements as far as cam recommendations. Imca rules iirc require a 6200 chip for a crate and 7000 for an open motor, not that you need to spin it that hard.

My hat is off to you for running a Mopar, can’t think of anyone doing that anymore, good luck and keep us informed on what you find out!!!!
 
Many years ago a guy on Moparchat was racing a bmod type car up in north-south Dakota, he popped his good motor and was doing good in points so he put a bone stock 360 in it, it would float the valves at like 5500 so he geared it to run at maybe 5300 or so, this thing you would think wouldn’t even hang with anyone. He ended up running mid pack and was able to stay in the points hunt till he got something better built, quite a good story.
I never ran a automatic, used a old three speed in high, so I’m out of the equation on a converter for this application.
 
I never ran a cam with more then 274/274 or 228/230 @50/108lc had plenty of torque coming out of turn, and in drive /3 gear you will need a 4.56 gear on a 3/8 high bank track or maybe a 3.91 in second gear remember the race is to the flag not the end of the track, cam for torque not hp the carb in the resistor plate .
 
I never ran a cam with more then 274/274 or 228/230 @50/108lc had plenty of torque coming out of turn, and in drive /3 gear you will need a 4.56 gear on a 3/8 high bank track or maybe a 3.91 in second gear remember the race is to the flag not the end of the track, cam for torque not hp the carb in the resistor plate .
We’re you also on dirt?
 
If you are running a stock oil pan don't turn it over 5500 rpms or it will blow up the high bank tracks will kill a mopar engine quick because the oil pan sucks for this type of racing, windage tray is a must have also don't use a high volume oil pump .thats why you don't need a big cam because the rpms are low finds one that peaks hp at 5000 rpms but keep compression high with a tight lobe.
 
63 dart stock car. 360 2bbl 3.73 rear 904 trans 9-1 cr. 3/8 mile high banked dirt track. next engine build, on hand I have a new converter specs say 4000-4500 stall (advertized?) and a howards hyd cam 71841-09 specs say rpm range 2300-6000 intake duration at 050 is 235 ex dur is 243. advertized dur is 289 intake/297 exhaust. intake lift .488 ex is .480" lobe seperation is 109. do these sound like good choices or should I see if I can exchange em for another cam/tq if the companies will allow that? thank you for your time. RR
Which tracks are you racing at?
 
Potomac speedway md, 3/8 heavy bank hagerstown MD 1/2 mile little bank
 
eagle (nebr) for sure, maybe beatrice. I have some 4.11's for the 7&1/4 (welded spiders). do you think that would be low enough or I have an 8&3/4 & a pumpkin & spotted some 5:13's on ebay for cheap.
 
I think Howards will let me exchange the cam & PTC will mod the converter for me when I have all the needed info (their spec sheet in online).
 
eagle (nebr) for sure, maybe beatrice. I have some 4.11's for the 7&1/4 (welded spiders). do you think that would be low enough or I have an 8&3/4 & a pumpkin & spotted some 5:13's on ebay for cheap.
I think they run 6.20' s with a crate motor and that chips at 6200. Open motors run 7000 rpm. I can ask one of my customers to verify a gear for an open motor. You should check with IMCA and see if you can run a shorty header now that they are approved for the chevys. Is your motor is set up to run 7000?
 
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