back cut large valves or not? on a 402 CID..

[Marc Haibeck]

I think that it's interesting to note that Lotus added a back cut on the intake valves for the 405 HP '93 - '95 engines.

I always have the early intake valves back cut.

[wfot]

Paul, thank you for the insight. I can appreciate the not divulging others information. I do not remember the thread that I read that trick on but obviously it stuck in my mind. I cannot see the picture you posted, any chance you could re-post/message me it? It could be a picture of a cat, but I am curious..... lol

Marc always a pleasure and as always, appreciate your input.

I was going to back cut both but I realized I am thinking of airflow in the opposite direction on the exhaust... the air flow tests that I have been watching that back cut the exhaust flow test that change with air flowing in the OPPOSITE direction of what the engine would see. A look at the exhaust valve finds that it does have a ridge, however the back of the valve is extremely clean, so I am leaving it alone.

the intake has a strong ridge and has build up all over the back face of it, so back cutting or blending that out from the seat is in order.

again appreciate the input,

time to get dirty

John

[wfot]

I was wondering about the valve lifters...
I understand that the factory lifters are heavy, I was wondering if anyone has tried or knows of a lighter lifter? I thought I read somewhere that a cosworth lifter was much lighter and would drop in... of course I would want to know if someone has tried this AND if it works of course...

John

[Paul Workman]

Originally Posted by XfireZ51

Paul, didn?t you also shave the heads a bit?

Yes, now that you mentioned it. As I recall it was no more than .020" (if that), more for truing up the surface "while I'm in there" (reverting to my SBC hot rodding dayz) than anything else.

I might add (under the careful guidance of Bob Gillig too) that there is some slight modifications to the chamber as well, so the increase in measured compression "before and after" is not as much as one might expect, after having milled the heads (now maybe ~ 11.5:1 vs. stock 11.0:1 [as I didn't CC the chambers afterward]).

[Marc Haibeck]

Hi John,

I have used lighter lifters. It was at the special request of a customer and it worked out well. INA part number F-46516 is the same as the OE LT5 lifter except:
- It has an open internal construction that makes it 24 grams lighter. The OE lifter weighs 74 grams and the F-46516 weighs 50 grams.
- The height is .045" less. This preloads the plunger less. The OE lifter is preloaded .080". The F-46516 preloads .035". (.080" - .045" = .035")

The lifter worked fine with maybe a little tappet noise. The F-46516 is used in VW diesel engines.

I have not used the light weight lifter in another engine because I don't see any value from it.

[wfot]

again, Marc, thank you for the information

Did that motor rev better? higher? 24 grams x 32 would be a total of 768 grams, I guess that would only be 192 per camshaft. But it is going back and forth like 3500 times a minute...

What about titanium retainers? I know that is a popular thing? would that be worth the weight reduction in the valve train? what would be the weight savings on a titanium setup?

Then I question stainless valves.. is there a weight gain (loss) to using stainless valves vs stock valves? then if the valves are oversized then what weight does that add?

keeps me up at night...

John

[Jagdpanzer]

The stock valve train can rev safely to 7200 rpm which is well above peak power for the majority of LT5 street engines. Installing higher reving valve train components results in little to zero payback for the spend. However, for a serious 8000+ rpm competition engine lighter lifters and titanium retainers makes sense.


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[wfot]

Agreed phil,
I have heard of several stage 3 cammed big CID motors getting to 7,500 - 7,600 RPM and this is the neighborhood I would like to be in. So yes considering the Ti retainers and the light weight lifters. however, I am well aware of how finicky these motors are with non-stock parts so this is what is making me think everything thru as thoroughly as possible.

I bet you will be making the 421 sing a little higher with the new exhaust....

and any input experience is welcome..

John

[Marc Haibeck]

We also added power to the engine so that it did accelerate faster. What the lighter lifters contributed was mixed into the overall results.

LPE was a major supplier of Titanium retainers. They used them on all of their engine packages. They stopped supplying them over ten years ago.

Be aware that people experimented with LT5 engine speeds over 7600 rpm long ago. They learned that the OE chains go out of control and break above 7600 rpm. I'm aware of two LT5's that normally run to 8000 rpm. I don't know how they do it.

[Jagdpanzer]

Imagine they are running Jerry's stronger IWIS secondary chains
https://www.jerrysgaskets.com/chain-...e1607869129850


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