What's the diameter of LT4 hot springs? Does anyone make a spring that will handle a .576 lift and is the same diameter as the LT4 springs? I don't want to pull the heads to have them machined for a stupid cam swap.

 

K-Motion springs Part#KMO-K-750 You can get them from summit or jegs. They run about 129.00 bucks but have the same diameter (1.265 ) as the LT1 and LT4 springs. They also are good for up to .600 lift. I just built up a set of LT4 heads and I used these as well on my 383. I also used KMO-K-7500 retainers and KMO-K-6130 locks. Hope this helps.

 

Thanks man.

 

Would the L98 valve seat work with those springs?

 

id recommend against using a 1 and a quarter spring on anything over .500 lift..having that much lift the springs will start to "wobble"...not only will that tear up the guides, possibly bend a valve but itll cost a helluva lot more then it would be to upgrade to 1.45 springs,..hell go all the way and get a dual spring..then youll really be worry free

 

I would tend to agree with this advice. You could consider the Crane dual springs that have a 1.46 OD. Crane 10308-1 Spring kit w/99893 springs $149. These can handle .600 lift.

 

Won't I have to have the heads machined to accept the larger spring? That is what I am tryng to get away from. If go through all the BS to remove the heads, AFR 195's are going back on. Is there a way to machine for the larger springs without removing the heads?

 

Yes, and machining the head on the car is not a great idea IMO.

 

Not for the Crane 10308-1 Spring kit .

 

The 10308 springs will not fit on Lt4 heads I went through this.
Get the kmotions,they were not out when i was having troubles.I ended up using the crane h11 tool steel valve spring and have not had a problem yet.The cranes are good up to .600 lift as well but it was a tight fit on the spring cup as I recall because they have an inner damper spring.Good luck.

 

I've been doing a little research on the 10308 Crane Kit. Apparently it will install without machining the heads but every reputable machinist I've talked to recommends against that. As I understand it the spring will have a tendency to "walk" around the head. It is apparently especially dangerous to use the shims that come with the kit as the valve seat, they're too thin for this purpose.

It's definitely a pain to pull the heads for this purpose, but better than risking it with an "iffy" spring combo.

That said they're are stock diameter springs available that will handle the lifts that you require. The K750 is one, (single spring), and I know that Combination Motorsports sells some as well, that I believe are doubles. Call them, they're hard to get on the phone but once you talk with them you'll be glad you did.

I also think SkarodM would be a good guy to talk to, pretty busy guy but very knowlegeable.

 

Hmmmm. Thanks for the info guys.

 

Thats why you dont use the shim.....you get the cups and no worry about walky

 

I couldn't have said it better. Just use those Crane supplied hardened .015" shims as shims for height adjustment. I got a set of Comp Cam's seats that fit and used them. A tight fitty and no walky!