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

[wfot]

Hello all,
building a 402, 4 x 4 square motor.
I have a set of large valve heads. I think they are 90s. It appears that the porting was done by someone who knows what they are doing. they came with a package of parts that were all gathered for a 402/427 build.
Ports at the mouth are 37mm. Valves are stainless steel, 40.2mm and 36.7mm. planning on stage 3 cams.

The valves have a slight lip above the seat.... my question is should this lip be blended into the back of the valve for a smooth transition or left alone?
I think blended, this has always worked for me in past for other, non LT5 engines but I know this motor is particular with certain things.... hence want to ask before I do..

thank you in advance for any thoughts on this.
John

[Jagdpanzer]

Can you show us a photo?

[wfot]

sure can. I tried to angle the valve to be able to see the edge. It is there, you can feel it...

[Jagdpanzer]

Check put this Speed Talk discussion on back cutting valves
https://www.speed-talk.com/forum/viewtopic.php?t=46843

[Jagdpanzer]

Another reference
http://www.ws6transam.org/afrflowdata.htm


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[wfot]

thank you. excellent info.
I do have to keep in mid at what lifts the flow numbers improved/got worse. I am planning on stage 3 cams and they should be about .44 lift, so they would be nothing like the .6 lift numbers.

I am now thinking of just blending over the intakes...


another thought is a Siamesed runner plenum or a reduced runner plenum. I want the torque but the HPs as well...

[Paul Workman]

My valves were back cut, and I "siamesed" the plenum runners (somewhat) internally, leaving only ~ 1.5" of a septum between the runners at the plenum outlet leading to the IH; leaving a leading "razors edge" on the septum (to reduce reversion leading into the septum).

I did fully port the runners, tapering from 37.5mm from the plenum into the IH and into both runners of the heads, and tapered and shaped the head passages (avoiding entering coolant or oil passages) and bowls. And, the exhaust ports got some special attention as well.

I have yet to port the THROTTLE BODY, which Marc says will likely give me perhaps another 4-6HP. And, with some special tweaking (phasing) done by Pete Polatsidis on my stock cams, AND dyno tuning by Marc Haibeck, I was pleasantly surprised by the 'before n after' results (graphed below).

[wfot]

Impressive. the curve stays much flatter after the work. do you have any pictures of the bowl area?

The block I have, i believe, was done by Krichner (sic), I believe he block was used in Kirt white's 415. 12mm studs on all mains. The heads are probably done by krichner as well, the work is top quality. I did find a few variations on the ports mouth at the head, most are 37+ a few are under. I will be correcting this..

my understanding is that most builders, not lt5s, SBC, back cut the intake and not the exhaust. If you compare before and after flow numbers, the back cut does hinder some flow over .500 inch. but under .500 there is almost always a flow improvement. I feel that the multi valve engines can benefit from better low lift improvement and will not suffer the high lift problems of 2 valve motors...
I also heard there was an exhaust port trick on the LT5 that takes away the point just where the ports meet in the middle... if that shape edge is removed, it is worth about 10 hp... this has been done on my heads.

I appreciate the input/comments

[Paul Workman]

Impressive. the curve stays much flatter after the work. do you have any pictures of the bowl area?

The block I have, i believe, was done by Krichner (sic), I believe he block was used in Kirt white's 415. 12mm studs on all mains. The heads are probably done by krichner as well, the work is top quality. I did find a few variations on the ports mouth at the head, most are 37+ a few are under. I will be correcting this..

my understanding is that most builders, not lt5s, SBC, back cut the intake and not the exhaust. If you compare before and after flow numbers, the back cut does hinder some flow over .500 inch. but under .500 there is almost always a flow improvement. I feel that the multi valve engines can benefit from better low lift improvement and will not suffer the high lift problems of 2 valve motors...
I also heard there was an exhaust port trick on the LT5 that takes away the point just where the ports meet in the middle... if that shape edge is removed, it is worth about 10 hp... this has been done on my heads.

I appreciate the input/comments

Yes, Ryan (a builder now in Phoenix, last I heard) told be about this trick too. Easy enough to do, so I removed that sharp junction in my exhaust ports as well.

No pix on the bowls OR the exahust ports (sorry). But I followed Ryan and Pete Polatsidis's advice and enlarged (slightly) the intake bowls AND removed the tights and all castings resulting in what would be an impediment to smooth air flow (in and out of the cylinders). NO pictures, as I promised Ryan and Pete I would not divulge specifics. But, there are dozens of books written on the subject and lots of examples (photos) in the public record.

One of my favorite examples that clearly demonstrates the principals of what good porting should look like is captured in this picture of a pair of Webber velocity stacks...says it all. This is not from an LT5, mind. But, it does say volumes to those with the least bit of curiosity about what good porting should endeavor to accomplish in the end...hint, hint!

.

[XfireZ51]

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

[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]

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:dontknow:]).

[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-rh-secondary-cam-timing-iwis-90-95-11c4/#PhotoSwipe1607869129850


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[A26B]

Imagine they are running Jerry's stronger IWIS secondary chains
https://www.jerrysgaskets.com/chain-rh-secondary-cam-timing-iwis-90-95-11c4/#PhotoSwipe1607869129850


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Affirmative

[wfot]

Marc, thank you for the input. I understand that the stock computer has its highest rpm a fuel adjustment can be changed is 7,000. to get the engine "fueled" after 7,500, you need to trick it a little and after 8,000, there is no real way to alter the fuel curve. I was wondering if the engine was allowed to bounce or stumble above 7,500, if that would create the same jerking situation as a bad injector?? and if the chain was allowed to slap around long enough it would fail...

I was considering Jerry's chains, thought it might be a little overkill, but then again that is what I am trying to build, right?

Jerry are those chains in a 350? and/or a big inch motors? Any feedback on how many miles they have gone or service life yet? And what about the crankshaft chain? any aftermarket progress on them?

again thank you guys for all the info/input
John

[Marc Haibeck]

An LPE Titanium valve spring retainer weighs 10 grams. The OE steel retainer weighs 19 grams.

The spark and fuel tables end at 7000 rpm. The last datum in the table applies from 7000 to 7500 rpm. I would expect that the system would use the 7000 to 7500 rpm value beyond 7500 rpm.

[wfot]

Marc,
Yes I agree, that is what I have found. the main tables allow for changes for 7,000 and they should hold until 7,500. after that you can't really put in exactly what you want.

and thank you for the titanium weight information. so I am thinking with 9 gram on the retainer and then 24 grams for the lifters, I would be lightening the valve rotating weight by about 33 grams per valve. I think with the stage 3 cams and 7,500 limit, it might would make a tangible difference. I will be happy to report my findings if I ever get it together AND it runs.....

I already have Jerry's cam followers ready to go in.. still on the fence about if the chains are worth the squeeze. I do not think there is ANY aftermarket crank to cam chain gears chains available.. Correct??

John

[Marc Haibeck]

The OE type primary chain is all that you need. I have never heard of any problem using it. Install it with new facing on the tensioner.

[wfot]

The OE type primary chain is all that you need. I have never heard of any problem using it. Install it with new facing on the tensioner.

OK good enough for me on the primary chain and I have jerry's facing for it. So done on that.

thank you sir