74 LS4-454

Starting 3 weeks vaca today, going to make a serious effort to get the 74 Vert back together and running with the rebuild of the LS4 454. Looking back over the last 5 years, and I question why did I take everything apart? But this where I am now and really looking forward to getting back into the rebuild mode.

The engine is apart down to the cam, pistons, rods, and the crank. As mentioned before and on the recommendation of a member I purchased an ISKY 270/280 Mega Cam. Here are the specs....

Intake Timing.................................. Exhaust Timing
Duration: 270 DEG...........................280 DEG.
Open 21 Before TDC.................... 74 Before BDC
Close 69 After BDC...................... 26 After TDC
Cam Lift: .310 ............................... .323
Valve Lift: .542 .............................. .565
Valve Lash: .000 HOT ....................... .000 HOT
...................... COLD .................................COLD

Overlap: 47 DEG.
LOBE CENTER 114 DEG.
Rocker Ratio.... 1.7

Not totally understanding all of the #'s like members in the know, I have some questions and do need opinions and suggestions.....

I intend on not touching the bottom end as the cylinders still have the crosshatch markings in them, (engine only has 10,000 original miles). I have been advised not to even pull the caps with that little mileage on the engine.
Using 68 427, #215 closed chambered heads that I purchased years ago that are completely redone and have larger valves, 2.19's & 1.88's and the chamber are 100 cc's. Also using stamped rocker arms as opposed to rollers, a 69 427/390 aluminum factory intake, either the original Quadrajet or a NOS still in the box, 1970 454 replacement Quadrajet.
Probably use the original distributor and convert to electronic.
My goal was and still is to have a BB that will spin in the 5500-6000 rpm range and not run out of breath at 4500 r's like the stock LS4's did.
I know I have mentioned some of this in previous threads during the past few years, but this is now crunch time, and I don't want to put an engine together and not be happy with it. From what I understand I can use the open chambered pistons with the closed chamber heads and still raise the compression 1 to 1 1/4 points, which would bring me up to around 9.5 compression.
So with all this being said.....

1- will this build provide me with a smooth strreeable idle and the necessary vacumm with the Turbo 400 & A/C? Because if not, I will sell the ISKY and get a different cam.

2- are there any changes you would make from what has been stated?
I am also using the TH 400 and the stock converter.

3- recommendations on any specific brands for rocker arms, push rods?

4- I think I have the gasket suggestions written down from a previous thread, but are there any newer type gaskets (for the entire engine) that I should consider?

5- I know I have asked this one before also, how do I determine the correct head gasket to use with this set-up? do I need to take any specific measurements?

6 and finally for now.... would you use a head bolt kit or a head stud kit for the heads?

As always any and all opinions, suggestions are always welcomed and appreciated from all of the knowlwdge that this forum has to offer.

Thanks again..........................Tom

jnb5101

The only two things that I can comment on are the NOS carb (replace the accelerator pump with the ethanol resistant type), and the head studs(you won't be able to raise the heads enough to clear the studs in the tight engine bay, in case you want to pull the heads in the future).

74 LS4-454

appreciate the reply.....taking notes....thanks....Tom

cv67

regular old headbolts. Some bowl/short turn work canhelp things out some
vacuum would be Ok wiht that cam. Isky 280 would really spin up to 6 but youll suffer with manners....some. 270 is a great street cam.

labhound

Sounds kinda like what I want to do to mine, but, I figured if I'm down that far into the motor,I'd swap the pistons to make it around 10.5:1. I have no idea how many miles are on mine though.
Let us know how it runs !!

TimAT

Double check using open chamber pistons and closed chamber heads. I recall somewhere that that will not work. The dome shape and the combustion chamber shape will cause them to hit. Not good.

labhound

If it's all stock '74, they are dish pistons.

74 LS4-454

just double checking on the cam....will keep it....


hopefully it will run.... I have enough $$$ into it already, and not worried about another point, if I get around 9.5:1 I'll be happy

they are not dome pistons.....hopefully they will be fine....

yes all stock and dish pistons......

Les

Although I'd like to see the duration numbers at .050, the cam should give you good performance and good street manners too.

With flat top pistons you're probably OK, but it's always a good idea to check for valve/piston clearance once the cam is degreed in by using the clay method. With the bigger valves in those heads it should be a potent street engine.

74 LS4-454

another positive response for this cam set-up.....
just wanting to make sure I do everything right......thanks for the advice........

427Hotrod

Did you special order that cam? MegaCam's usually have tighter LSA...like 108? That 114 is going to make it smoother...but give up some low and midrange power.

If someone didn't do some bowl work in those heads when they installed the larger valves, you're leaving a lot of power on the table.

As mentioned...double ck PV clearance...especially the edges of the valve pockets with the larger valves. Do your pistons have valve notches? Some were pure flat back then.

I'd install a stock pump with the High pressure spring to get a little more pressure in it.

Double ck your rockers to make sure they can handle the added lift. You can get stamped long slots if needed pretty cheap.

What pushrods are in it? 5/16" or 3/8"? Make sure the new heads have guideplates that match. Much better with 3/8".

What springs are on the new heads? Can they handle the lift and more aggressive cam? Are you pulling the inner springs for break-in?


Years ago in high school we did a 454 in a buddy's '71. We left low compression and added an LS-6 solid lifter cam, a Tarantula intake and an 850 Holley. It ran mid/high 12's on street tires through 3.08 gears/4 speed and iron manifolds.

The old big blocks can be woke up pretty easily.

JIM

JIM

74 LS4-454

Jim, no special order, it is listed in their catalog.
Bowl work, etc., everything that could possibly be done to the heads was done, with the exception of opening up the intake ports.

Yes the pistons have valve notches.

I have a new stock fuel pump and will add the spring.

I think my pushrods are 3/8's I have the guide plates from my old heads. I do need to buy new pushrods.

The springs came with the cam kit, and I think have 135 lbs of pressure installed.
Not pullimg the inner springs for break-in....is this something I should do?

Thanks for the info....appreciated.....still need to know what size head gasket to use. I think you may have responded to my thread of over a year ago with that info....need to look that up!!!

Nice changes on your buddy's 71.....
I just want to have a 454 that will rev to 5500-6000 r's and not feel like it is out of breath.
Even if it only wakes up half up, I will be happy.....

Thanks for the reply......................Tom

c6silver

I think I'd want a more modern cam on a 112 lobe separation (or even a 110), that Isky cam is OLD technology...does this car have headers ? What trans and rear gear ?

hugie82

When I did my 427 I had the raised trw pistons with open chamber heads with a cam very similar to yours. It was a dog! A friend sold me closed chamber with oval ports. They worked much better with 98cc chambers. I think my pistons had a 7cc dome.
Moral to the story, compression must match your cam or you'll be unhappy

74 LS4-454

No headers, TH 400 & 3.08 gears....Which cam would you recommend?


So are you suggesting I should look into different pistons if I stay with this set-up? What compression ratio would you suggest???


Appreciating all of the replies, as I could never figure out which set-up to use.....

c6silver

Comp Cams XE274 at least, maybe the next size up. Are you keeping the TH400 and 3.08s ? I'd look into converting the TH400 to a Switch Pitch torque converter set up if so...It allows you to change the stall speed of the converter and it gives cars with high (low numerical, like 2.73 or 3.08) more grunt off the line. You're fine with the pistons you have and the closed chamber heads. I'd look for a Buick 455 Qjet (800 cfm). Cut down the center divider a half inch between the secondaries ONLY on that intake. I'd have the manifolds ported and put a 2.5" Pypes X pipe exhaust under the car while you're there. Shoot for 9:1 maybe 9.5:1 if you can get it, make sure the cooling and fuel systems are up to it, and make sure your cold air cowl induction works.

hugie82

Summit has a good compression calculator to get your exact compression. If you have a good cooling system , I would go 10.5 to 1
I was over 11. To 1 with no problems on nj pump gas 93 oct. My heads were milled .020 but stock they were 98cc. I personally would rather have a little to high compression and adjust than hit to low and have a slug around town wasting gas....

427Hotrod

I'd use a steel shim headgasket either from GM or maybe Mr Gasket still has them. Something like .020". I'm assuming the pistons are down in the hole at TDC .017"-.025" or so?

I was thinking about the oil pump spring. I'd like to see 60psi+ at high RPM.

Make sure the springs are at the correct installed height. They need to be measured closely. A few .000's change things a lot.

You're not using a crazy cam there....but these days it never hurts to break it in on just the outer springs. It's a PITA...but it will certainly help ensure everything gets acquainted properly during break-in.

The Isky cams have been around a long time..but Isky stuff often ck's out a lot healthier than advertised. I wouldn't discount them. Plus for reliability, old school stuff isn't a bad idea,



JIM

c6silver

I think 11:1 is pushing it for pump gas in summer heat with iron heads...aluminum heads, fine no problem. If you do go for 10:1 or more keep the cam you have on the 114 lobe separation, but make sure the tops of the pistons are carbon free and de-burred and that the chambers in the heads are polished up decent and de-burred also. I'd look at some 1.8 roller rockers too to jack up the lift and take advantage of the porting work with that gentle ramp cam

If you want to avoid changing out the inner springs on the heads for cam break in, consider another "spare" set of heads with just identical outer springs just for cam break in, then swap heads after...still a HUGE PITA, but may be easier (and safer than dropping an oily, slippery keeper into an oil passage) than doing springs on the motor in the car...if you break the cam in on a dyno then it's less of an issue.

The Switch Pitch setup is really neat and isn't hard to do (Google it)...basically, you change the front pump/input shaft, the converter, an electrical connector and a few other odds and ends. You can use an 11 inch converter from a Buick ST300 or an Olds Jet Away trans for more stall speed than the 12 inch big car (Buick, Olds, Cadillac) converter. These are really made for mild big block engines like the LS4 and "highway" gears. Big car 12" TH400 switch pitch converters are about 1800 low stall and 2600 to 2800 high stall. The 11 ST300 or Jet Away is 2300 to 2500 low and 2800 to 3000 high. The 67 Olds W-30 used an 11" converter behind the 400 inch Olds big block. The torque multiplication effect of the vane angle change in the switch pitch converter makes a car with 2.93 gears accelerate like a car with 3.42 or 3.55 gears, and is almost like having a poor man's overdrive (letting you gear the car for highway driving and giving stronger torque for around town and passing on the freeway).

hugie82

He's got a lot of duration for the street and I had a little less dur with over 11 to 1. I do understand the caution. If there's any sharp edges on a piston or head inside the chamber could cause a hot spot for detonation.
He is in an either/or situation. Either you run compression at the upper limit or you change your drive line ie; stall speed, rear axle or trans to have a fun responsive ride. I'm basing my comments on the choice of cam that was given in the beginning of this thread.

I think he has a good set up and a few tricks can make it a badass street car! but before the first bolt is torqued down he needs to get a good idea where his compression is.... As mentioned before, if his pistons sit far down in the hole, that can be a full point right there. Same with head gaskets. I would spend the money and get MLS gaskets that usually crush down to .030 when torqued.

2 parts popped in my head that are cheap but are needed. A steel sleeved HD oil pump drive and the MLS head gaskets. I've blown a head gasket and it was an expensive mistake. The metal ones are good but you need perfect decks to avoid problems so I'm an MLS fan now!
Another part that would be very beneficial would be an adjustable timing gear set and timing cover. Think of it as oops insurance on your build. Too much compression, retard the cam. Too little, advance the cam. You can dial the motor to your driving style without pull the motor apart