OK, I am doing a cam swap in my 383 and was working on the valve springs. I bought the car with the 383 all ready in it, and it was supposed to have an LT4 hotcam, and LT4 valvesprings. My new cam was way too much lift for the LT4 springs so I ordered a set of 600 series spring from combination motorpsorts.

Fast forward to today. I notice that the new springs look a tad narrower in diameter than the old, so I bust out the tape measure ans sure as **** they are. The new springs measure 1 1/4, just like they should, but the old springs meaure 1 5/16. So my question is, have the valve spring seats been machined to accept the bigger springs? Or are LT4 springs infact 1 5/16" in diameter?

If the heads have been machined, I'm pretty much screwed right? I would need a bigger diameter spring.

Thanks guys!

 

Having your heads machined doesnt mean that you cant use a smaller diameter spring. As far as I know, I thought the LT4 valve springs were able to be used on a stock LT1 head without machining. But if your heads happened to be machined, its not that big of a deal. It just means that down the road you will be able to upgrade to a larger spring without much work. I would recomend getting spring seats/locators for your springs if you havent allready bought them. Im sure someone else will chime in here.

Brian

 

All things considered a smaller OD spring should be o.k. if you match it with the appropriate sized spring seat.

 

If you suspect that the seats have been machined you need to check the retainer height. You might have to shim the springs to get the correct installed height. If not your valve spring pressure will be off.

Daren

 

I agree. Definitely check these items. I hope you have a spec sheet on those springs. I think a barrel micrometer is almost mandatory for correctly setting up springs to achieve correct height/spring pressure and to avoid binding.

 

You guys aren't answering my question. I guess I should of been more specific. I know machining the heads does not allow for the use of a smaller diameter spring, that's not what I want to know

I was told my car had Lt4 valve springs on it. I was under the impression that LT4 valve springs are 1.25 inches in diameter. I was planning on doing a cam swap, and did not want to remove the heads to have the spring seats machined. So I began to look for a valve spring that would accept the lift of my new cam (.575) and was still 1.25 inches in diameter. I found a spring that met the rquirements and went ahead and bought them.

During the install I noticed the springs on my car (supposedly LT4's) were bigger in diameter than my new springs. After I measured them the springs on my car were 1 5/16 inches in diameter. The new springs are 1.25. SO I have a couple questions:

1. Are LT4 springs 1.25 or 1 5/16?

2. Would you have to machine ther stock spring seats in an LT1 head to accept a 1 5/16 spring?

3. If my heads have been machined ot accept the 1 5/16 springs, will it be OK if I use a 1.25 inch spring, or do I need to go bigger?

Thanks guys.

 

I believe LT4 springs are 1.31" O.D. Since they can go in an unmachined LT1 head, you should be able to run 1.25" springs with no problem, since those are the diameter of stock LT1 springs.

 

Thanks man!