[The WidowMaker]

motor is going 30 over and in my quest to find some new cheaper forged pistons, i had narrowed it down to the speed pro l2256 (+6.1cc). but, they are over 600 gms w/out the pin, they have a .060 offset pin bore and they have 5/64 / 5/64 / 3/16 rings grooves. even though the motor is most likely going to be sold, i want to put some better pistons in it and build it a little better. i found the l2490's (+3.4cc) that are closer to 400 gms, have a center pin and 1/16 rings.

problem is im running the gm hot cam and its too small for the compression im going to make with the smaller reliefs of the 2490's. plus, ive always wanted to put a bigger cam in it anyways 218/228 @ 50 and .525/.525.

so im looking for a new cam. 3.73 posi / tko600 / 29" tall tire / mostly street car with emphasis on pro touring abilities (good all around 2500-5500 but still making pwr to about 6200).

i need to keep the lift below .515 with 1.5 rockers and .550 with 1.6. i need to reuse the lt4 springs that came with the hot cam (101 seat, 331lbs./inch)

im looking at the lunati 54761 with the following specs:

298/286 adv
227/234 @ 50
.478"/.480"
.510/.512 with my 1.6 rockers
112/108 lsa/lca

it looks like the intake adv duration is higher on the base but lower on the 50 as compared to the exhaust. i think this would work well with the poor flow on the exhaust.

what do you guys think? is it worth the swap? i think the lighter pistons with the bigger cam will make a big difference. right???

thanks, Tim

 

[trmnatr]

It would probally run better on a 110* lobe seperation but what is your compression ratio?

 

[Dave427]

I would run the Hot Cam that you already own, thats an awesome cam.

Dave

 

[The WidowMaker]

i just ran it through the dcr and its way too low. even though the 50 specs arent too bad, the 298 intake at .006 is killing me. it only came up with 7.75 dcr. if it were 286 id be right at 8.21. right now the hot cam is 279 at .006.

anybody know of a good HR cam that wont require a change of the springs?

thanks, Tim

btw... thanks for all the help with the previous posts....

 

[trmnatr]

A tighter lobe seperation would help or maybe some more advance??

 

[The WidowMaker]

advancing another 2 for a total of 6 still only gives me 7.9 and tightening the quench from .039 to .035 gives me 8 flat. im still looking for another .25.

how much is too much advance for a cam. i know harold recommends right around 6 deg. Is this intake ramp angle too shallow? thats a lot of duration at .006 for only 227 @ 50. i really want to get that valve open quick to take advantage of the vortecs flow.

tightening the lsa doesnt change the ica and therefore doesnt raise the compression any.

thanks for the help, Tim

 

[novaderrik]

how much compression do you have- and i don't mean the DCR.
the HOT cam was designed to be used in the 96 Corvette LT4 engine that had 11:1 compression. i had that cam in a 355 with vortecs and 10:1 compression, and it was a beast from off idle to past 7000 rpm. the power just kept coming. and it idled silky smooth at 800rpm with 17" of vacuum.
just skip the pop up pistons and get some 2 valve relief flat tops and run the thinnest head gasket you can find to get the quench nice and tight.

 

[The WidowMaker]

the 2490's are a flat top with 2 valve reliefs and they put me right at 11:1 whereas the 2256 with 4 reliefs put me at 10.6.

its kind of confusing depending on how you look at it, but +cc's are for dish and flattops, whereas -cc's are for domes. dished pistons add to the compressed volume and domes take away from it.

the hot cam has been a great cam and made tons of power with the old combo, but i was just looking for a little more since i have to change pistons anyways.

derrik - what was your full combo.... quench, pistons etc...?

thanks, Tim

 

[fabio]

if you're going to sell the engine I would run the 4 valve reliefs and keep your current cam. Run a thin head gasket to keep quench tight. Vortecs do respond to a bigger duration @ .050 cam than normal with a 8-10 more on the exhaust.

 

[sschevellefan]

the 2490's are a flat top with 2 valve reliefs and they put me right at 11:1 whereas the 2256 with 4 reliefs put me at 10.6.

its kind of confusing depending on how you look at it, but +cc's are for dish and flattops, whereas -cc's are for domes. dished pistons add to the compressed volume and domes take away from it.

the hot cam has been a great cam and made tons of power with the old combo, but i was just looking for a little more since i have to change pistons anyways.

derrik - what was your full combo.... quench, pistons etc...?

thanks, Tim

I think your addig it up wrong. your not going to get 11:1 out of a flat top 350. About 10.6 is the most I`ve seen. The 2256 pistons won`t giive you more than about 10.25:1 because of the valve reliefs. I agree if your going to sell it anyway, don`t spend more than you have too. As for the cam, I would just run it myself. I have heard it`s a pretty good cam. I recently bought a XR276HR and the specs are similar to the lunatii grind you listed except my lift is .502/.510 with 1.5`s. With my budget 383 build I`m going to use speed pro hyper dish pistons and the DCR cam in at a little over 8.2 and the static was 10.19:1

 

[kirkwoodken]

The specs on the Hot Cam are my favorites for a SB street cam. Sounds good, runs good, acceptable cruise mileage, at least for me. Use with close LDA (108) for a 302, wider(112) for a 350. Good broad torque range in a SB. I've never run this cam without headers, so can't say how it will do with stock manifolds. Probably not a lot of difference. Not enough cam for a 406, IMHO.

 

[The WidowMaker]

thanks for the replies.

specs to calculate compression ratio are as follows:

4.030 bore
62cc heads
4.125 x .039 gasket
0 deck
3.48 stroke
5.7 rods

it comes to 10.83 with the 3.4 cc and 10.5 with the the 6.1's and .039 quench
it comes to 10.95 with the 3.4 cc and 10.6 with the the 6.1's and .035 quench

 

[sschevellefan]

thanks for the replies.

specs to calculate compression ratio are as follows:

4.030 bore
62cc heads
4.125 x .039 gasket
0 deck
3.48 stroke
5.7 rods

it comes to 10.83 with the 3.4 cc and 10.5 with the the 6.1's and .039 quench
it comes to 10.95 with the 3.4 cc and 10.6 with the the 6.1's and .035 quench

You are right, I was using the wrong head gasket bore size. Sorry about that.

 

[The WidowMaker]

i do agree that the hot cam is awesome. most guys dont give the heads or the cam enough credit, but it has been real strong for me. i drove the car with this motor as a daily driver for 5 years (end of high school, and beginning of college) before letting it sit for the past 4 years. but since im putting money into it, i figured i might as well see if i can get some more power out of it.

for those that havent read my other posts, this motor will either go back in the car for a few years or just be sold. plans are for a big inch sb with either a dart or lsx block. not only am i not sure which route to go yet, i still need to convince myself that 20k+ is a good investment in this car (frame off is close to this alone).


thanks, Tim

 

[novaderrik]

derrik - what was your full combo.... quench, pistons etc...?

thanks, Tim

i can't remember the exact numbers, but the pistons were some now discontinued lightweight forged TRW's with 2 valve reliefs that i got a deal on. they were pretty damn light.
they were at the stock .020 below the deck, with a cheap set of .015 victor Reinz steel shim head gaskets for a .035 quench. the machinist that did the work on my motor said it spec'ed out at just a hair over 10:1 with those gaskets, and 9.5:1 with the thick el-cheapo gaskets that i originally put in it. it ran much better with the thinner gaskets- 4 degree less total timing (34 vs 38), a couple degrees less initial (16 vs 18), and no detonation on 89 octane gas where the thicker head gaskets rattled on 93 octane. i think i was running AC R44LTSM plugs- it detonated on AC Rapidfires and Autolite Platinums, but not the cheap AC's from Wal Mart. but it's been a few years since i traded the car away, so the heat range might not be right.
but whatever the exact specs were, it was a beast and i wish i had that motor back..

 

[trmnatr]

When calculating DCR you use your @.050" closing point and add 15-17 to that to figue it out, the keith black site has a calculator that seems to work pretty good, try that out. You need to match our static compression to your cam duration/lobe seperation/ area under the curve and your dcr come out to whatever

Just to note: Alot of small block chevy race engines turning 7,500rpm-8,000rpm have dcr of around 8.6-9:1, you dont need to try to get it as high. Your running pump gas, right? 222/230 ish @.050 108* lobe center is your compression is 9:1 {static} to 10:1 or if you have 11:1 go up to 232/240 ish @.050 on a 108* or 110* lobe center and be done with it

 

[trmnatr]

Some classes of super stock engines are running 8:1 dynamic compression ratio's

Dynamic compression is like cylinder head "wet flow" when on the engine but if you the buyer puts too much thought or effort into it, even us the engine builders, we will mess up our entire engine package

We leave it to the designer to do all of this for us. 8:1 dynamic ompression is good for your application