Budget 318 build

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I have 2 sons that are heavy into computers (which is good) but they were never interested in hanging out in the garage with dad. You're a lucky man.
 
dartfreak75 said:
To my understanding the 85-89 318 had a higher compression 9to1 due to the closed chamber heads (302) 9 to 1 is higher than any 360 and higher than the later 340 so how would a 340 cam (basicly what the sum6900 is) kill my power?
Click to expand...
Well, the Mopar 'factory' numbers were always high. I just ran some numbers with:
  • the 302 heads and 62 cc chambers
  • Felpro 1008 head gasket thinner than the standard Felpro head gasket but you can go 1 step thinner).
  • the best CR pre-Magnum factory pistons, which sit around .075 down in the hole and have 4 small valve eyebrows (And we don't know which ones you have)
That combination is right at 8.3 SCR; that is pretty typical, and I find the real SCR numbers usually are around .7 to .8 point lower than the factory SCR numbers. So you are starting with an SCR that is about 1.4-1.5 points lower than the real SCR of a factory (early) 340. That is how it will hurt the low RPM torque.

Now lets put your cam in there and run the DCR (dynamic compression ratio number); this is what sets the low RPM torque, which is what gets the car moving from a stop unless you rev it up a lot to get into a higher RPM range (hence the suggestion for a lot higher rear gears and a lot higher RPM torque converter). The DCR is at 6.5 now, even with the cam advanced 2 extra degrees to help the low end DCR. Your cylinder pressures are gonna be in the 115 +/- range IF the rings seal well. Again that is lower than stock 318's..... which is sensible with a larger cam.

For Perspective: 6.5 is lower than the stock 318 DCR and lower than the stock /6 DCR. So, for low RPM's, this engine is going to 'lazy' at best.

For reference, I once ran a 300+ duration cam on a 7.6 SCR.... DCR was in the high 5's LOL. That engine was truly, truly dead below 3700 RPM: had to rev it up there to get a good launch; yes, I could putt around below 3700 RPM but it would not take off if I pushed the throttle. The only things that saved that engine was that it could rev to 7700 RPM all day long so I had at least a 2:1 usable RPM range, but that is narrow for street use. Oh, and that was with a 4 speed....

So the suggestion of a 2800 RPM torque converter and high rear gears is spot on. At least you have the better breathing on the high end, but with the heads, your real usable torque range is going to be narrow. OK for drag racing, not so much for street cruising. This cam is an older, low stress-on-the-valvetrain design. Low cost (which is good for sure) but sloooow ramps and long tails for a late intake valve closing which is lowering the DCR as explained above. It is a good cam for plonking into a stock setup and valve springs, since it does not have a lot of lift or fast ramps.

I indeed 'get' your plan to just get this 318 running and then move onto the 360; it certainly does not justify much more than a simple rebuild. I would just not put that cam in there and expect it to be a perky street cruiser. So I'd suggest a different cam for this with 2-3 steps lower duration. Something like a Lunati 10200205 is the ticket IMHO:
  • .441" intake lift vs the K6900's .421" lift so bit better mid and high RPM HP, so the top end is maybe extended a few hundred RPM (though that may be more limited by the valve springs)
  • 18 degrees shorter duration so the DCR is now 7:1...getting back to stock 318 levels so the lower usable RPM range has been extended down around 500-700 RPM.
  • Moderate ramps and lift so you can run it with the stock stuff
  • Only a $19 more on price from Summit, but you have to wait 2-3 week for it
Hope that helps. Are you still looking at valve springs?
 
nm9stheham said:
Well, the Mopar 'factory' numbers were always high. I just ran some numbers with:
  • the 302 heads and 62 cc chambers
  • Felpro 1008 head gasket thinner than the standard Felpro head gasket but you can go 1 step thinner).
  • the best CR pre-Magnum factory pistons, which sit around .075 down in the hole and have 4 small valve eyebrows (And we don't know which ones you have)
That combination is right at 8.3 SCR; that is pretty typical, and I find the real SCR numbers usually are around .7 to .8 point lower than the factory SCR numbers. So you are starting with an SCR that is about 1.4-1.5 points lower than the real SCR of a factory (early) 340. That is how it will hurt the low RPM torque.

Now lets put your cam in there and run the DCR (dynamic compression ratio number); this is what sets the low RPM torque, which is what gets the car moving from a stop unless you rev it up a lot to get into a higher RPM range (hence the suggestion for a lot higher rear gears and a lot higher RPM torque converter). The DCR is at 6.5 now, even with the cam advanced 2 extra degrees to help the low end DCR. Your cylinder pressures are gonna be in the 115 +/- range IF the rings seal well. Again that is lower than stock 318's..... which is sensible with a larger cam.

For Perspective: 6.5 is lower than the stock 318 DCR and lower than the stock /6 DCR. So, for low RPM's, this engine is going to 'lazy' at best.

For reference, I once ran a 300+ duration cam on a 7.6 SCR.... DCR was in the high 5's LOL. That engine was truly, truly dead below 3700 RPM: had to rev it up there to get a good launch; yes, I could putt around below 3700 RPM but it would not take off if I pushed the throttle. The only things that saved that engine was that it could rev to 7700 RPM all day long so I had at least a 2:1 usable RPM range, but that is narrow for street use. Oh, and that was with a 4 speed....

So the suggestion of a 2800 RPM torque converter and high rear gears is spot on. At least you have the better breathing on the high end, but with the heads, your real usable torque range is going to be narrow. OK for drag racing, not so much for street cruising. This cam is an older, low stress-on-the-valvetrain design. Low cost (which is good for sure) but sloooow ramps and long tails for a late intake valve closing which is lowering the DCR as explained above. It is a good cam for plonking into a stock setup and valve springs, since it does not have a lot of lift or fast ramps.

I indeed 'get' your plan to just get this 318 running and then move onto the 360; it certainly does not justify much more than a simple rebuild. I would just not put that cam in there and expect it to be a perky street cruiser. So I'd suggest a different cam for this with 2-3 steps lower duration. Something like a Lunati 10200205 is the ticket IMHO:
  • .441" intake lift vs the K6900's .421" lift so bit better mid and high RPM HP, so the top end is maybe extended a few hundred RPM (though that may be more limited by the valve springs)
  • 18 degrees shorter duration so the DCR is now 7:1...getting back to stock 318 levels so the lower usable RPM range has been extended down around 500-700 RPM.
  • Moderate ramps and lift so you can run it with the stock stuff
  • Only a $19 more on price from Summit, but you have to wait 2-3 week for it
Hope that helps. Are you still looking at valve springs?
Click to expand...
Thanks for your help yea im looking at springs I actully already have the 6900 cam so im not buying it I do have a question on the headgaskets i bought the felpro set 2114 what is the headgasket thickness on them arw they thicker or thinner or the same as stock?
 
As far as the piston heights i haven't pulled the heads yet i was gonna check my cylinder pressure and if it was good i wasnt gonna pull them at all
 
dartfreak75 said:
Thanks for your help yea im looking at springs I actully already have the 6900 cam so im not buying it I do have a question on the headgaskets i bought the felpro set 2114 what is the headgasket thickness on them arw they thicker or thinner or the same as stock?
Click to expand...
Comp Cams #901 springs will work good.
 
I’d install the cam straight up and not worry about it.
Valve spring wise, check the springs pressures as well as dimensions against what is stock and what is recommended by Summit as a matching set of springs for the job.
 
dartfreak75 said:
Also with the cam i have do you think i should advance the cam
Click to expand...
Understood on the cylinder checking procedure as you have it. It would indeed be good to have the numbers with the stock cam still in there. Is this a cranking compression test or a leak-down test? I thought the engine was out and torn down...?

I would assume that the Felpro set has the 8553PT head gaskets; those are gonna be .020-.030" thicker than the stock ones, which is another 3.3 to 5 cc's of chamber volume...ow! The thinnest that you can get inexpensively for higher CR is the Mr Gasket 1221G's at .028" thick.

Ah OK, the cam is there.... yes I absolutely would advance it. I'd set the ICL at 104 or 102. 4 degrees advance makes a very noticeable improvement in low RPM torque and throttle response. I can't see from the Summit page what the ground-in advance is (where the advance would be with the cam installed dot-to-dot) but I'd guess it is 108. So another 4 degrees would get you to 104 (if 108 is indeed the cam's ground-in advance).

I'd advise doing the cam timing properly; you need to borrow a dial indicator, or figure up a way to have a definite stop on the cam at .050" intake lifter lift. You can get a free printable degree wheel here:
The Machinery Cleanery Universal Timing Disc, Degree Wheel, Downloadable - Goniometro per Messa in Fase dei Motori a 4 Tempi -
I use that and glue it to poster board and VERY carefully cut out the center hole to maintain accuracy.

And you are right on one thing.... at least you don't have the older large chamber 318 heads!
 
I ran some numbers on the dyno with the information at hand. If you have the tools, I would degree the cam but
Capture.JPG
I would put the cam in straight up. I don't think low rpm torque loss is a problem. There's a pretty flat torque curve between 1000 and 4000 r's where you spend most of your time driving.
 
4° advanced lost 10 hp @ 4000 rpm but increased torque by 4 ft. lb. @ 2000 rpm.
 
I'd use the VS-1120's before the 901's for this cam and application. Spring rate is 343 vs 387 lbs/in and that is plenty IMHO for what you have in terms of top end RPM and ramp rates. Both are fine for coil bind here. And low cost!
 
toolmanmike said:
4° advanced lost 10 hp @ 4000 rpm but increased torque by 4 ft. lb. @ 2000 rpm.
Click to expand...
Understood and thanks Mike. I've done the 4 degrees advance thing and found what it will do.... and don't think I'm not a believer in computing tools.

Forgive my ignorance but it has been a while since I ran that type of tool...what is different between the 2 sets of TQ/HP columns on the left of the table/graph?
 
toolmanmike said:
The Mellings are the same outside diameter but they don't have open pressure specs (more important I think) like the Comps do but Comp doesn't list the seat pressure. What does Summit recommend for the cam? Like Rumble said, that's what you should go with.
Click to expand...
Comp seat load is 104 per the Jegs site..... take that as you will!
 
nm9stheham said:
Understood on the cylinder checking procedure as you have it. It would indeed be good to have the numbers with the stock cam still in there. Is this a cranking compression test or a leak-down test? I thought the engine was out and torn down...?

I would assume that the Felpro set has the 8553PT head gaskets; those are gonna be .020-.030" thicker than the stock ones, which is another 3.3 to 5 cc's of chamber volume...ow! The thinnest that you can get inexpensively for higher CR is the Mr Gasket 1221G's at .028" thick.

Ah OK, the cam is there.... yes I absolutely would advance it. I'd set the ICL at 104 or 102. 4 degrees advance makes a very noticeable improvement in low RPM torque and throttle response. I can't see from the Summit page what the ground-in advance is (where the advance would be with the cam installed dot-to-dot) but I'd guess it is 108. So another 4 degrees would get you to 104 (if 108 is indeed the cam's ground-in advance).

I'd advise doing the cam timing properly; you need to borrow a dial indicator, or figure up a way to have a definite stop on the cam at .050" intake lifter lift. You can get a free printable degree wheel here:
The Machinery Cleanery Universal Timing Disc, Degree Wheel, Downloadable - Goniometro per Messa in Fase dei Motori a 4 Tempi -
I use that and glue it to poster board and VERY carefully cut out the center hole to maintain accuracy.

And you are right on one thing.... at least you don't have the older large chamber 318 heads!
Click to expand...
Thank you for that link that is very helpful i was gonna buy a degree wheel that is awesome thanks. As for the pressure test yes the engine is out and partially disassembled the heads are still on everything else is off i was gonna put the new cam in and then turn it over by hand with a pressure gauge screwed in the plug hole one at a time of course is that a good way of doing it? I have done it that way before. As far as the head gaskets go id be better of compression wise is to not pull the heads off?
 
@nm9stheham

Can’t see cam specs? Hocus-pocus Alecazam! Poof!
There ya go bro!

Cam specs are:
1200 - 5000 rpm
278/288 advertised
204/214@050
.421/.444
112
 
nm9stheham said:
Understood and thanks Mike. I've done the 4 degrees advance thing and found what it will do.... and don't think I'm not a believer in computing tools.

Forgive my ignorance but it has been a while since I ran that type of tool...what is different between the 2 sets of TQ/HP columns on the left of the table/graph?
Click to expand...
The bottom graph is manifold pressure and volumetric efficiency.
 
So when i degree the cam the centerline should be 112 is that what that last number means
 
I had that info RF360, but tnx. What I haven't found is the ICL listing. Is it 112 or 108 as-ground, or ..? Good point on leaving the heads on for the thinner OEM head gasket.

OP, turning by hand will usually give low compression numbers.... unless you are reeealy fast and strong and young LOL. I like to have 5 pressure strokes per cylinder at cranking speed so that is 80+ rotations at speed.... but you may be up to it! It'll be worse if the rings or valves are leaky but the lower DCR will help. Any way to bolt up the trans put on the starter? Or is the trans still in the car?
 
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