After reading all the talk on chevytalk.com and pro-touring.com, I think I will toss the EFI idea for a couple years. I'd sure be alot more comfortable tuning EFI than a carb, but the systems are still too expensive for what I do with my car.
So now comes option #2, which is to bump the CR from 10.14:1 to 10.7-11:1.
From talking with Pat and Harold, I have come to take it that my cam as lashed .016/.018 (cams specs in lobe catalog: 287/291 @ .020 256/260 @ .050 172/175 @ .200 .643 lift w/ 1.7 rocker, (.3780 lobe lift), so .661 lift with my 1.75 RAR rockers) produces a seat duration of roughly 291/295, (if I read our previous post about where I should actually be measuring being about .013, where harold kindly offered his opinion of my actual seat duration at (I should be calling him this week for a 302A6LUN for my LS5 Rebuild) which is quite a bit bigger than the big 287/291 comp I thought was being installed, despite my recommendation to the for a 287/295 UD roller per Harold.
Using the DCR calc, and my following specs,

Crank Stroke 4.00
Rod Length 6.385
291 adv intake, 295 adv exh
112 LSA 104.75 ICL
4.282 bore
Deck .002
Gasket .039
Head CC 116.5
Piston Dome 23

The only item I guess on was head gasket bore, which I just decided was 4.3. I honestly have no idea.
This got me a working DCR of 7.76.
I don't know how much more I can mill my heads, or whether a thinner gasket is avail. for a BBC (like a .015 shim type that is safe for street and occasional strip use, and I will not swap pistons).

Using the following guesses, I get the following results:

.015 gasket:
8.16 DCR 10.67 CR

.015 Gasket, 114cc combustion chamber
8.34 DCR 10.93 CR

.020 Gasket 114 chamber

8.25 DCR, 10.8 CR

.020 gasket 116.5 chamber

8.07 DCR 10.56 CR.

This is assuming my 291/295 measured seat duration math is correct. I could be pushing it here.
So if I go back to 287/291 as my advertised in pats calculator (which I know is not true because my lash is .016/.018, and the 287/291 is at .020), I go to 8.21 DCR 10.56 CR with a .020 gasket (if they make one).

My overall point here is whether 1) it is safe to assume that the 291/295 #'s of where I should be doing my DCR math are correct,
and 2) is it worth it to boost a DCR of a max 7.89/10.14 (with the 287/291 in the calc) to a min of 7.76/10.14 using the 291/295 #'s, and bring it to 8.25-8.35 DCR, and still be able to run on 93 octane pump?
I am only expecting one more track outing this year due to time constraints, this would be done after the track outing, but before it snows. I have estimated a 3 to 3 1/3 percent gain in converter efficency at the top end and I am still wondering if this will be worth any MPH when I hit the track and shift right.
My previous best MPH was 116.62, on a very hot and very humid day, I have run 116.02 or 116.03 on all other runs on very hot and humid days as well, but I have yet to return to that 116.62 or 116.63 runs I had. I am hoping a 3% more efficent converter could toss on maybe 2mph or so, but who knows.
I do know with disastrously low shift points of 5900 1-2 and 5400 2-3 with a converter that seems to flash between shifts to 5000rpm (judging by one video on the highway of my tach), I ran a 12.1 something at 114.98 with a 1.94 60x, versus my 11.8 @ 116.03 with a 1.825 60'. I limit myself ET wise here with small tires because I don't have a cage. I don't want to turn this into a book, so I will try to stop talking now. All roughly positive comments are appreciated..

I hope this made some sense to someone..

If not, let me know and I will try to clarify my scatterbrain here..

Matt

The smallest gasket bore for a .039" FelPro is 4.370" according to Summit's catalog. I don't know if a thinner gasket is available. I'm sure you could have them made in copper. You can't use a gasket thinner than about .030" with the .002" deck you speced. I see you already have the cam advanced as much as is reasonable. I can't think of any way to raise the CR other than milling or changing pistons.

Thanks Pat.

Are copper gaskets OK for street use? I am not sure how much more milling my heads can take, I guess I would have to call Dart and ask. They were originally 119cc I think, but milled down to 116.5 when I had the engine torn down 2 years ago. The builder at the time asked if I wanted to go higher, but at the time I was running a 286 adv 230 @ .050 hyd cam, and he said he was doubting any more CR would be safe, so I backed off.
I will try dart, or perhaps someone knows around here. They are the 320cc runner rect ports, I don't believe the exact model head is still made. I could grab some numbers off the head if needed to though.
In your opinion (or anyone elses) if I can either go with a combo of a thinner copper gasket and some more milling, is it worth my time to have a stronger runner or are any potential gains outweighing the work here? I don't want to touch the pistons because that would involve new rings, maybe rod bolts, so on and so forth, to the point where it would become a total engine teardown that I don't need yet.

Thanks.

matt

Grumpyvette at Chevytalk uses them all the time. I've never used them. You might try ask him about them. I think you would pick primarly bottom end torque by raising the CR. However with rect ports, you need all the bottom end you can get. See how much more you can take off. If it were me I'd head in that direction. Have you calculated the chamber size you need? Angle milling might be necessary.

Thanks for the help Pat. I will call dart and talk to them as well as consult the guy who did my cam swap (he also builds/tunes engines, but most of his clients are all blower crowd guys).

I would like to get a little more low end grunt out of this thing, its there, but you need to wait for the converter to kick in sorta, its like it has 2 cylinder shut off below 2600. My dad drives the car as well and thinks I exaggerate this, but I can notice it. Its sort of a non-issue at the track I think because of the converter, but then again its hard to tell. Comparing back to back cams on the dyno (same dyno, cam swap guy dyno'd the motor before swapping cams so I could compare), you can see a strong downward dip at 2500, so I don't think I am too off here. I think some increased cylinder pressure with my big runners and wide LSA couldn't hurt. I can deal with having to pay for cylinders to be milled and checked and maybe new pushrods if they are the wrong length, but I don't want to get in much deeper than that.

matt

Have you tried opening your lash up to the max to shorten the cam up even more, then try a run or two to see if you do get more lowend b/c if you do, you are overcammed slightly, imho..

pdq67

.006 straight mill off the heads equal approx. 1 cc reduction in chamber volume on a typical 118cc open chambered bb head.

your reduction from 118 cc to 116.5 was a .015" flat mill that was taken off your heads.....

with your cam i would not be affraid to run 11 to 1 compression at all.....i have never used the dcr caculation in anything i have built(thats not to say it shouldnt be used or anything like that)i can just tell you from experiance what i have built and done and seen others as well build.

i just dont think you should rely so heavy on caculations there are way to many variables that come into play that even a caculator cant compute

as far as changing gaskets that i wouldnt recommend....i like to see the safety margin for piston to head clearence there. and your pretty safe with what you have.i have on my own bbc's run right down to .033 clearence and saw piston contact to head during a tear down. so i keep my bbc at .040" or more clearance.

shaving the heads would increase the compression but i myself dont like to go wild on this because it throws the valvetrain off....i like to keep milling as a last option to increase compression.

with what you have and the limits they you have put on yourself i would mill another .015" off the heads this would increase your compression to about 10.3 to 10.4 to 1. any more then i feel you will be looking into having to change push rod lengths.(it might not be a big deal to some but i perfer not having to go thru the hassle) the only reason im saying that is because im sure you had some taken off the block maybe around .020" give or take to get at the .002 deck you have now. plus you have another .015" off the heads now.....add another .015" if you go that route all this milling is adding up......and at least for me i perfer to keep it simple and not mess with the the valve train and intake angles.....

i feel that you would be better served with oval port heads since you are shifting so low in the rpm range you are giving up alot of torque.


increasing you intake charge velocity would help out your entire rpm range since your shift point is well below the rpm potential of the heads.

i think with an intake change ,slight compression increase,and alittle more dialing in of the timming and carb you should see some better improvements....

i think i read in some other posts your shift points are limited for one reason or another and you are not gaining nothing beyond 6000 rpms.

im throwing some ideas out here and not trying to hammer on anyone advise.....

It's true, getting the quench tight does involve some risk. In my SB I found the pistons hit at .021" and probably .026" would have been OK. But this engine has forged pistons with rather tightish clearances (.004" piston, 1.800" rod) so piston rock and rod movement aren't big issues. I was going to suggest opening up the lash but, judging from your past post, I figured you were pretty much wedded to it. Dennis makes some good points, perhaps taking a bit more off the heads and living with it is the best way to go. Even with milling another .015" you might need to cut the intake and get new pushrods (although, measuring and getting custom length pushrods isn't a big deal). Oval port heads would help a bunch. Rect's are for high rpm.

Thanks for the help. Not sure what I will do, I might just leave it alone. The best thing would probably be close to 11:1 oval ports, but I don't feel like dealing with that right now.
I have considered opening the lash to .020/.022 which is as high as the guy who installed the cam said I should go if I were to test it. I thought the cam was too big initially, but he insisted it wasn't. I don't think I lost a ton of power, but I did lose some by going a bit big. And its true, engine dyno data showed no real point in going much beyond 6200, chassis dyno showed a flat point until 6500. But thats it, no more extra juice beyond that.
I'll probably leave it alone and try to get to another test and tune this year, and then try opening the lash next year.
Changing pushrods I wouldn't care, but if I would have to start paying to have the intake milled to match the angle on the heads so everything meets up, then I'm screwing with too much stuff to make it worthwhile.
So I guess for now I'll just leave it be, since the hassle to benefit ratio is not extremely favorable.

Thanks for the help though.

Matt

Hey Matt,

What brand of pistons are you using? Are they SRP's? If so, I'm not sure that your dome cc's are correct. If you are running the longer rod (6.385"), the SRP piston for that (I thought) were 26cc and not the 23cc that you stated. The SRP 23cc dome pistons I believe are for the stanard length rod.

An extra 3cc would make a big difference.

The data I have for the dome CC came from the guy who tore down the engine and CC'd the heads.
I asked him to write down as much stuff as he could, but there are no part numbers. They are SRP pistons.
When this engine builder tore down the engine, we bumped the CR from 9.6:1 (CR from when I was using an UDHR4) and moved it up to 10.14:1. I would assume he knew the correct CC of the piston?
I honestly don't have any other way to tell. I am not saying anyone is wrong here, I honestly don't know what to think :confused: .
I know I have the long rods because that is on the bill from the first buildup of the engine. Unfortunatley the first builder of the engine didn't keep a record of the parts he used and I really got was a bill with a PN here or there when he called for specific $$ to buy a specific part, I think he just called and said I want to go long rods with this motor, and the pistons & rods are blah $$.
So I am not basing this off a PN that may be wrong, but from the info I have from the rebuild of the engine.
I would assume the guy who was increasing the CR of the engine would have the correct CC of the piston written down. Do you guys think there is a possibility of a mistake here...?
Any ideas?
Then again I just grabbed my photocopies of the paperwork and the guy who tore down the engine wrote my rocker arm ratio as 1.7, the guy who did the cam and said he always takes specific precise measurements of RAR says they are 1.75 RAR.
I assume there is no easy way to figure this out..

matt

I just looked at flat lander racing's site, and indeed the SRP piston they list for a 6.385 rod is 26cc dome, not 23.
The parts in the engine were bought ~9 years ago. I don't know if that would make a difference.
What do you guys think?

The parts list from the teardown goes as follows:

Gm 454 block .030 over
SRP pistons .030 over
Eagle Rods +.250
Gm 4.00 stroke crank 10/10
Dart 320 Rect Port Heads
1.7 rocker arm ration

c/r
Bore 4.282
Stroke 4.00
Deck .002
Gasket .039
Head CC 116.5
Dome 23

and he adds this up to ~10.14

Thanks in advance anyone who can help here.

Matt

Matt,

Don't remember for sure but did you post recently that you have the Crower Stainless Steel roller rockers? Those are the ones that I'm running with my Isky street roller and I can't remember for sure but I thought that the ratio is etched or stamped into the body of the rocker arm. Might check that, should tell you for sure.

I am running the crower stainless rollers. I will go out and look this evening. I have a little more faith in the attention to valvetrain geometry and stuff like that in the guy who did my most recent cam, irregardless of cam size/selection, so I bet it will say 1.75 if its on there. I will check it out. The guy who did the teardown also made a mistake on the install height of my springs, and I am pretty lucky that something didn't let go up top they way there were set up.

thanks.

matt

Matt, stick a smaller cam in well advanced to gain max velocity out of the heads. If it doesnt both ET and MPH better, I'll eat my Team Chevelle t-shirt.

Thats sitting on the back burner. I'll run it again this year with the new converter, next summer try opening up the lash a bit to see if I can maybe fool the engine a little, then I will go smaller the following winter. The reason I bowed out on this cam after some argument with the cam guy was that it didn't occur to me (not dealing with solid cams before) that it would be quite a bit bigger as lashed than the .020 in the comp cams lobe catalog. He does really perfectionist work, but I think he missed the boat a little on duration.
Its certainly not a dog, but there is a schooch missing from what I expected. I'd go back to a hydraulic roller with a 242/248 or 248/252 @ .050 if I didn't already own these Isky Red Zones. A smaller solid roller may be the ticket, but I gotta try all the tricks I know to see if I can get this cam to push my land yacht to 120 in the 1/4. One thing I will have to watch out for if I do spring for a new cam next winter (not this one) is if my rockers are 1.75, what would be acceptable solid roller lift on the street turns unacceptable (from my point of view anyway). I am gonna give this one a try with the converter, then the lash, then call it too big. Plus I might be able to recover some of those gallons per mile ;) that I lost somewhere along the way..

Matt

Dang, in a self-serving way I wish SOMEBODY would try the SR version of my Pro-Street cam! ;)

That is the same thing that I have been thinking.
I think the roller version of Gene's cam would be perfect. graemlins/thumbsup.gif

276/284, 245/253, .660"/.660" 108-110LSA

That is the cam I will most likely go with if I ever change out my "old design" Isky street roller.

Matt, you can have your Comp Cams reground to the Lunati's specs. Most cam regrinds are usually around $100-150.

i was just reading some of the post and one thing i noticed i left out of my earlier post when i said change intakes i was talking about putting a nice oval port intake on your rec port heads.........i have done this in the past and saw about 3 mph gain and and i believe right(if memory serves right) around .4 tenths drop in e.t. it helped out my 60 ft time alot but this was on a 396 with rec port stock head and i was only turning it to 6500 no where near the potential of the heads.....i had boworrowed a dual plane performer from a friend and it worked......i later changed the combo shortly after to oval port heads, cam, and intake......so i really dont know what just a head and intake swap only would have done.....but i know the end result with oval port heads and several changes like cam intake and carb it was faster then my rec head version........

maybe this might be something to tinker with some call it a band-aid others i have heard they swear by it......i tried it .......it worked but it wasnt what i was looking for.....i still wanted more low end grunt then what i was getting...........

It sounds like it is overcammed and the heads are to large for the intended rpm range. What is the cranking compression of the current combination?

Scaled down, but similiar. I will be putting the Comp XR274R SR in the 408 motor. 274/280, 236/242, .639/.645, 110LSA. The install got postponed, probably for the best, I am going to make a valid attempt to get a baseline for a before and after comparo, just for info sake.

Originally posted by GRN69CHV:
I am going to make a valid attempt to get a baseline for a before and after comparo, just for info sake. Joe,sounds good.Keep us posted..I think your current combo with the flat tappet Crane will do just fine at the track graemlins/thumbsup.gif
Then,you'll have some real #'s to compare the cam swap to

I tried running an edelbrock oval port RPM on the engine on the dyno when I had the motor torn down.
I lost about 30hp and gained zero torque, even down low. maybe a different manifold would have worked better, but that combo didn't help.

Matt

Matt, you're doing much too much ratiocination to cover an incorrect cam choice. ( I know it was the builders choice, but.... )