Hey group. My motor is 496 w/topline aluminum rectangel port heads. comp xr 294 roller. 242/248@.050. holley 870 avenger on a pro products single plane rec. port intake. msd ignition and 2" primary hooker heades.

here is what i have run into. car does not have power until 4000. not a whole quicker than my old 383. but once you get to 4000 rpm it goes like snot. my question is am i leaving that much torque on the plate with my intake.

i have ordered(should be here friday)a dual plane air gap. so the pieces are there. i just hope that with the new manifold i lowere the torque curve and pick up my power between 2000 to 4000 rpm. what do you think?

thanks tommy

How much rpm do you turn? The air gap is good to 6500, I'd think it would help,and we'll be waiting anxiously for your test results.

sounds like you need about a 4000rpm stall convertor. how big are the runners on those heads? i'm sure the rpm intake will bring the powerband down some, but it isn't going to perform a miracle. do you have any actual track times to go by? or are you just judging by the seat of your pants feeling? usually any motor under 500 cubes with large rec port heads needs at least a 4500rpm convertor, IMO.

With a few assumptions re your combo, your hp peak with that cam is around 7500. So your operating window is something like 5500 to 7600.

4 speed car. no, no track time...just seat of the pants, kinda. the heads have 320 intake runners. actually according to comp the cams rpm range is 2500 to 6500 max and i think more like 6200. thats why i got it. i did not want a high winding motor. the intake was just stupidity. i thought my options were limited with rec. port heads. but that will soon be rectified.

thanks tommy

reading another post...about rec. port heads. maybe me over headed :D

The cam may be rated for max 6500 rpm, but not with the heads you've put on. Do you have the flow numbers for those castings? What is your Compression ratio? The intake was a good choice for the heads and cam, but the whole top end package is for a high rpm motor. A dual plane will help, but you're robbing peter to pay paul, although I guess you have to do something.

No, the single plane on a 496 isn't stupid b/c you atre making the big motor easier to hook up b/c you are as said taking some from the bottom end to help the top end where hooking doesn't matter!!

I do feel the heads may be a schosh big though b/c JL said that a good set of large ovals can feed upwards to a 500" motor and even a 540..

As always, jmho..

pdq67

PS., I opted for cast-iron Merlin ovals for mine.. MY gut feeling is that a true large oval ported 290 cc head would be IDEAL for motors from 496 up to 525 or so, but only a gut feeling.. A 290 cc head with a 90 to 100 cc chamber would work great with flat-top pistons, imho!!!

yeah i was on the beam on heads and found a good deal on the toplines, so i figured i would have room to grow into them. well i didnt want to grow this quick. redface.gif it seems once again i go broke saving money :rolleyes: kinda stumpped now. i will try the new intake for giggles but with unexpected expenses on this car and a camaro i am trying to get running, heads at this point are outa da question. here are the flow numbers per topline:


Intake Port Test Data @28" of water
.100 .200 .300 .400 .500 .600 .700
75 158 230 286 34 380 403

Exhaust Port Test Data @28" of water
.100 .200 .300 .400 .500 .600 .700
62 118 160 195 229 248 265

compression ratio with the 119cc chamber is 9.5. thanks to all who have responded. any other ideas welcomed...shy of telling me what i now know graemlins/clonk.gif thanks again tommy


ps. found this link and made me scratch my head more. same cam as mine in one test heads similar(i know mine arent afr but these are rec. port)i have more stroke but less bore. i have a tad more compression. i know they are not apples to apples but maybe apples to apple sauce ;)

http://www.chevelles.com/cgi-bin/forum/ultimatebb.cgi?ubb=get_topic;f=4;t=015077;p=3

what do you all think? tommy

This whole Rec Port / Oval Port debate gets blown out of proporation at times. We just installed a GM 454HO crate (425 HP). 8.75 CR w/ Rec port heads, but it has a 214@ .050 roller cam. The motor is installed in a '66 4-speed car w/ 4:10's and 29" tall tires - has gobs of low end torque.

The 496 package you are using probably has "Too Much Cam"! Drop the cam down to 230-235 @ .050 Int and a use either a Dual Plane or a Small Single Plane, the difference will be quite noticeable. With a 496, you should have huge torque by 2500 - 3000 RPM. A roller w/ 242 @ .050 is equivalent to a flat tappet of 252+. The other thing is the big ?? Are you sure the CR is 9.5? I have been looking into 496 packages adn w/ a flat top and 119 CC Heads it is tough to get 9.0CR out of these without decking the block to Zero deck ht.

its supposed to have 9.5? we ran into the problem you mentioned with the pistions and i had a choice mill the heads or while the motor was being assymbled zero deck the block. i chose the block as the heads were already to go. just going by what my builder said. but i do be block was decked. that cam was chosen due to builder thoughts of stroker bleeding off some of the cam.

plus being a 4 speed car i usually am at 2800 to 3000 in cruise mode. not in the 2000 range. but this motor is dead to 4 grand. then like i said it pull like snot.

back to the cam. i can get take out 502 roller cams on the real cheap(pace, scoggins dickey and the like). if i get another cam that is three roller cams i have for this motor. the first being a retro fit in a new block and i did not feel qualified with end play of the cam button. then this 294 r and now what ever? i can start a big block roller cam store...my life long dream graemlins/clonk.gif graemlins/clonk.gif graemlins/clonk.gif

any cam suggestions?

the new intake will be installed regardless, i have one on my 383 and am quite happy. so that problem is fixxed.

i just found out that the motor is coming back out due to faulty oil pump so cam swap is piece of cake. thanks any and all who have posted. tommy

ps. is this why you all call it the DARK SIDE? :D

Correction there is no XR294R cam the highest is a XR292R...I assume you actually have the XR280R
Just to give you an idea of the XR292R cam on a smaller motor (higher revving)

I am running the same cam in a 454 +.030" over BBC. I am also running a Merlin Single Plane Intake with a 1050HP dominator. 11.5:1 compression and Dart 310cc Rect. Port Heads.

3650# car.
4.33 gear
4000 stall

I shift mine at 6800 and go through the traps at 7000-7200.

Best times so far:

1.41 60'
4.15 330'
6.50 @ 105.30 (1/8) w/(1.45 60' and 4.19 330')
10.64 @ 125.85 (1/4) w/(6.77 @ 101 1/8)

Car is capable of 6.44 in the 1/8 on the mild tune. Jumping up timing from 39° to 42° and rejetting the carb. would probably produce 6.35 @ 107-108mph in the 1/8

Mike recheck your comp book...not trying to an ars, because i honestly am so confused :confused: now i dont know which way to jump(and my best thinking has gotten me in this mess) :D that being said it is not a retro fit cam but a stepped cam for a gen v and vi. the number i put in the top of post is strait from cam card.

from my invoice at office...item #01-424-8 description CBVI XR294HR-10.

Which cam are you running the 280 or the 292? thanks tommy

ps quite impressive numbers. i'd take your times plus a second. graemlins/thumbsup.gif and be as happy as a clam.

Wow those are huge numbers on the heads, even bigger than I guessed at.
I think you really need to consult with a cam expert to try to tame those things. My first impression, and i could be wrong , is that you should move away from the Comp grinds because of their relatively tight LSA, and look for something wider ( I know you have 3 on the shelf already $$$ ) to try and limit the overlap and build some cyl pressure down low. Again this is only my best guess, as I have no experience with big inch, big headed motors.
Also, what is the ultimate goal for this motor? Is it a street piece...

TJC, yes street piece maybe track some. now we are getting somewhere. but please dont forget those are toplines figures and from what i have read they are very generous. so far just one cam on the shelf soon to be 2 but that is cheaper than a set of new heads. maybe i should start a new post and see if harold will chime in.

like i said the motor has to come out next week for a new oil pump so the logical solution would be to re-cam then.

any cam suggestions would be greatly appreciated. gen vi block so stepped nose roller cam needed, any suggestions? thanks tommy

Here are the specs of the cam @.05 duration is 242/248. Lobe seperation angle 110 degrees That does not seem that huge to me. i have a comp xe284 flat tappet hydraulic in my 383 and the duration is only 10 degrees different and it pulls from 2300 to 6000. Also comps rpm range is 2800 to 6200. Did my heads foul that up this much? thanks tommy

67lemanster...sorry my bad...I am running the extreme energy solid roller...I assumed that and forgot they made a extreme energy hydraulic roller. Mine is the 11-773-8 (XR292R) Solid Roller

Mike not to worry...you took time out to help me! It seems the only bad is mine. But i know all the gurus here will help get my bad fixxed. tommy

wow, we have very similar combos. I have a 505 with pro topline rect. port heads (iron), a professional products single plane intake and a comp cams XE284 and 2" primaries. According to the dyno theres tons of low end torque, but I havent driven it yet so I cant really say...

please do a cranking compression test. my guess is you will have low cyl pressure. (less than 180 hot). in my opinion alum heads need at least 10.5 :1 static compresion , they suck heat out of the chambers and need more compression than iron heads to work well.i know quite a few people that switched from iron to alum heads and kept the same compression ,and picked up nothing.

67,

Your problem is definitely cam and compression.

Looked up the specs and ran it through the DCR calculator.

Your engine should have 8.9 - 9.0 static CR. The Comp XR294 int closes at 73 ABDC yielding a DCR of 6.75 - way too low. This all assumes a deck ht of .005 or less, .041 hd gasket and a Comb. Chamber of 119CC. If the cam is retarded the DCR drops to 6.50. Given your compression, you need to close the intake at 60 ABDC to get around 7.5 DCR. Something around 216 - 220 @ .050 in a roller will be real good. It will still pull to 6000 but you will pick up a lot of bottum end. Why not consider having one of the cams you have reground to a smaller cam?

thanks for your input. the one cam that is on the shelf is for a retro and since all this came up it went on ebay about 2 hours ago. so that one out. gasket is .039. i plan on a cam because it is needed. do they make a head gasket that has less compressed thickness? i think the one i have now is a felpro 1047.

better yet why not when the motor is out take the heads of and have them milled to maybe 110 or less combustion chamber to up the compression ratio. i dont know the cost but figure a cam this 250 minimum.

that way keep the cam and try and work with what i got. just a suggestion but it does seam logical? Yes. thanks tommy

ps. how does this work? i know we dont have the cam spects but it is a 9.14 compression engine?

Quote from another post:

Nope, it went in an original 66SS 396 4sp car & is driven on the street. The damn thing is so overpowered it's scary"
I am building the 396 for the owner & he is talking about putting the 489 in an early nova he has. Should be interesting [thumbsup]

BTW, Tony at AFR was just involved in a 502 crate build at Westec & it was OBSCENE It will be in one of the magazines shortly but it was a 502/502 made 530hp or so with headers & 740hp @6400 & 678ft lbs @ 5000 (over 670 from 4500-5500)with a set of 315 heads & I believe a Comp roller, not sure it was Comp but I think so. The compression was 9.14!, vic jr & 950hp

427L88,
Thanks, Them's our babies [Eek!]

Tommy,
I built the 496, actually a 489 in that post & all the specs are posted. The 502 was done by Westec & AFR. The cam was also 254/260 as I recall.
The 496 with the cam you are running & 10. compression made about 610 ft lbs @ 45-4600 & 620 or so at 5900
With no other changes other than a solid roller, 254/260 .698/.666 it made the same 610 ft lbs at almost exactly the same rpm but the HP was 670 at about 6300.
It had over 500 ft lbs from 2900 with the solid.
This was with an 850 Demon & Vic Jr with a 1" spacer.
This was on a dyno considered "conservative" by most. You could probably add 30-50 HP in the "good LA air" :D
The AFR heads are smaller than yours & just a super efficient head.
The low & mid lift numbers on the AFR's are excellent & are true numbers.
BTW, these heads were optimized for the larger bore & will flow upwards of 20 cfm more in some places just going from a 4.31 to a 4.530 bore adapter. 20cfm is a lot of power assuming you can use it & is partly why the 502 made such good power.
On my dyno I would expect about 40 less hp & torque but that doesn't take away from the fact it made some serious power.
I have not flowed the 320 Pro's but every Pro I have flowed was not even close in the low & mid lift range & the port was on the large side
also.
Three different 200cc sets I checked were between 205 & 208.
I cannot comment on your intake but on a 383sb I changed the intake from the Pro dual plane hi rise to an ede air gap with no other changes & it picked up about 15ft lbs & the same in HP.
Don't know if this is an isolated case but I now tend to stick with intakes I know work.
We did a 493 chry & there was about 30 ft lbs of torque between a Weiand team G & an ede perf rpm with no measurable loss in hp to 6000 or so (hyd cam)
There is no reason you can't make reasonable torque with that cam even at 9.0 with 500 inches but 10.0-10.5 would be a better choice.
I do think the heads are hurting you but I feel your choice of intake will help quite a bit to "cover them up"
I have to completely disagree with TJC about you having a 7500 rpm cam even assuming it were a solid. That cam will make peak power around 58-6200.
The peak power rpm of the engine is pretty much dictated by the cam unless the port has too small of a crossection & just putting on bigger heads will not move it up unless the ones you had were limiting it's potential.
It will be lazy with too big a head but this has very little to do with where it will make peak power, the power will just be less with to big a head & a cam that is designed for a lower RPM.
Same thing with a too small head & a cam designed for higher rpm.
Bottom line IMO is try the intake & see if you are happy. If not then look at the cam. This is assuming you are planning on staying with the heads you have ;)
Something I didn't see mentioned but you want the cam installed with the icl at 104-106, I'd opt for 104 with your compression

Originally posted by 67lemanster:
from my invoice at office...item #01-424-8 description CBVI XR294HR-10.
Tommy, I totally missed the Hydraulic roller reference..... excuse me. Mike is right.

Can you post your piston specs.

First off i want to thank all who posted and hopefully this will help some uniformed person like me down the road. This is a true case of buying cool parts that dont work together. graemlins/clonk.gif

So with that being said. i will try the air gap this weekend and make a few test drives to get a feel. unfortunately i cant put a 1" spacer due to hood clearance issures. If it does still not seem right i will then address

1. the heads. I will keep the heads i think they can be salvaged. But i will consider(read i will)have them milled to lessen the chamber and bring up the compression to 10.0 or 10.5. They pistons are flat top forged that are supposed to be zero decked. i will check and find out exactly how much in the hole they are or if it was done at all, once the heads are out.

Next question is will the intake need to be machined also to match heads?

2. Cam swap. something with less duration. the current cam was installed striat up.

thanks all and i will inform all after this weekend. tommy

I would just bolt the intake on & not port match it. Don't worry about the spacer, just try the intake.
If heads are done properly when milled you will not have problems with intakes as the intake side of the head would have been done to put it back where it belongs
Of course this doesn't look like it applies to your case :D

Set the intake on & the gaskets in place & see how the bolts line up. If they are high you will need to have the intake milled. Put it on with one gasket & see how it fits & you can estimate how much you need to cut.
For instance, if it bolts up good to both heads with one gasket you need to cut .030 off each side to make it line up with two gaskets.
If it seems low you need to cut less.
Confused yet :confused: :D

Confused yet? Oh, since Monday :D .

will bolt on intake and go from there.

I did talk to machine shop and he said .007=1cc. sure seems like a lot to get to 110cc or less chamber. if intake doesnt work will try cam. i will post results. Mike thank you for your time in this matter. Will talk to the thread on sunday. tommy