Reproduction 2.5" heat riser operation on 70 LS5

[Mathew S.]

I installed a new reproduction heat riser on my 1970 LS5 when I installed the exhaust. I checked the operation after working through some issues where not getting fuel above 4K rpm.

I put my iPhone under the car on video mode and revved the engine without load. The valve didn't move much, maybe 25% at most and revved up to upper RPM range. Is that normal, thinking it's not. Is it possible to easily remove one turn to take away some of the spring tension. Anyone experienced this before?

[Mark E.]

Re: Reproduction 2.5" heat riser operation on 70 LS5

Did these things ever work well?

Having the car judged? Wire it open between events.

Not judged? Replace it with a spacer.

Car will run better either way.

[Mathew S.]

Re: Reproduction 2.5" heat riser operation on 70 LS5

Not judging st this point, but maybe some point down the road. The 2" heat riser on the 70 LT-1 works like it should.

I would like like it to work as it should, but not sure if possible with the reproduction ones.

[Mark E.]

Re: Reproduction 2.5" heat riser operation on 70 LS5

As an owner of each, how would compare the driving experience of the LT-1 vs. LS-5?

[Mike F.]

Re: Reproduction 2.5" heat riser operation on 70 LS5

Your heat riser is functioning correctly, you will not see much if any movement without a load on the engine. Even when revving to redline.

I keep mine wired open between judging events.

[Mathew S.]

Re: Reproduction 2.5" heat riser operation on 70 LS5

The LT-1 is my fathers, and is almost identical to Terry's. The previous owner and dad did a little "street" race many years ago, and after about 100 mph the big block drive by. The cars are similar in driving experience except more weight in the front on the big block. The big block's fan is noisier, maybe due to it being an AC car, and there is more heat being radiated.

[Joe L.]

Re: Reproduction 2.5" heat riser operation on 70 LS5

Your heat riser is functioning correctly, you will not see much if any movement without a load on the engine. Even when revving to redline.

I keep mine wired open between judging events.

Mike and Mathew------


Yup.

Also, and by the way, the 2-1/2" heat riser valve is still available from GM under the original part number of 3887034. It's configured slightly different but it should be functionally fine.

[Mathew S.]

Re: Reproduction 2.5" heat riser operation on 70 LS5

I ordered it from Paragon so likely the same one, at least I would hope.

[Patrick H.]

Re: Reproduction 2.5" heat riser operation on 70 LS5

I ordered it from Paragon so likely the same one, at least I would hope.

You can hope, but I would not guarantee it.
I have found the aftermarket 2 inch heat risers to work poorly, so I have purchased some NOS 2 inch GM ones just to avoid having problems with them.