boostedbird38

iTrader: (7)

Hey guys, I just bought a bare set of brand new 243s and I'm going to swap my 853s valves in. Also, putting an MS3 cam in with 7.4 PRs and PAC 1211x springs.

Am I going to have a problem with piston-valve clearance/push rod length?

Is there a length difference between 853 and 243 valves?

Any harm in using my 109k mile 853 valves in the new heads setup?


Thanks in advance guys

Always2Slow

iTrader: (8)

Is there any harm like catastrophic engine failure? In short depends. What the problem with doing this is the valves are worn to your 853s heads seat. With factory tolerances varying from seat to seat and valve to valve you may or may not have a sealing problem when you install the new valves. It would be wise to check and at the very least hand lap them in. An even better approach would be to have them cut for a performance valve job. You will pick up flow and have a great seal on all the chambers. My second recommendation comes from checking the install height of each spring to make sure you have enough clearance from coil bind so your not destroying parts. Those springs are a bit on the weak side when it comes to seat pressure for such an aggressive lobed cam. I would look into dual valve springs that you can get 150lbs or more on the seat.

PhoneniX

+1 spend the money now and go with dual valve spring upgrade. heck you can find lightly used pac springs in the classifieds for great prices here usually. why risk 100k stockers

GiggleJuiced_SS

iTrader: (31)

Go for dual valve springs. Don't forget about the timing chain it should be upgraded as well. I would also replace the stock oil pump if you have the money. Its always cheaper buying good parts first. Gl.

redtan

iTrader: (5)

He's talking about the valves there having 109k not the springs. Nothing wrong with brand new PAC 1211x springs...

boostedbird38

iTrader: (7)

I did plan on having my valves lapped, at least.

So my springs are good? I was hoping so... their max lift is .625 which is well above the cam's max lift.

I do have a new timing chain and oil pump to put on. I've done alot of research for this build, I just had some specific questions...

So once I install the 853 valves in the the 243 heads will I have any p-v clearance issues?

Thanks for all the replies!

A.R. Shale Targa

iTrader: (2)

You can't just look at the max lift capability of a spring to determine if it will be right for XXX can lobe. The MS3 can is still one badass stick and TSP would most likely suggest good duals especially with the factory non hollow (heavier) valves. Also a performance valve job should be a must with so many miles on the valves.

.boB

iTrader: (1)

As long as they're in good shape, no reason not to use them.

Roll the stems along a piece of glass. If they're not straight, you'll feel it.

Have them refaced, and then lap them. Refacing will make sure the seat is round, smooth, and at the proper angle.

Lapping is a final finishing step to make sure you get a good seal. Some engine builders say it isn't worth the time, and some say it is. IDK if it helps or not, but I do it anyway.

boostedbird38

iTrader: (7)

Duly noted on the valves, I'll definitely get those taken care of.

Now these springs I have... Texas speed offers prc 1518 single beehive with the MS3 in a package deal.

So do i get rid of my pac 1211x for the 1518s?

Always2Slow

iTrader: (8)

No you get rid of your pac 1211x for the PRC .650 dual kit or go with the BTR .660 lift platinums.

.boB

iTrader: (1)

If the vendor recommends a specific spring with their cam, you should follow that recommendation.

The 1518 spring is from Precision Racing Components, not PAC. If you look on TSP's web page for the 1518, you'll find this statement: "Temporarily out of stock, if ordered the PAC 1218 will be sent as substitute"

What you have (1211x) is a step or two above the 1518's, but it's not a huge difference. Same installed height, lower coil bind point, and a little more pressure. I would use what you already own.