Call me crazy
Thread Starter
Racer
Joined: Sep 2017
Posts: 452
Likes: 55
From: Marianna Fl
Call me crazy
Seriously please do. So as I near the end of porting my 561 heads to go on to my L98, yes yes wrong heads ill get to that, and I was thinking. I need to buy a set of valves for this set of heads among other parts, because I'm on a budget I was thinking that instead of paying to have the heads milled out and new seats put in for a larger valve would it not be possible to run a smaller valve say a 1.84 in the same seat to remove some of the interference caused by a plate sitting at the end of the pipe. This comes down to a total of .05" smaller radius or 10% less valve face in the air charge.
I will be checking the size against my seats and with my head shop before making this jump but the logic sounds good in my head. Any experience with this would be appreciated. So about the LT1 heads on an L98. Some of you know its possible but I will be covering it in greater detail when I have pictures to show it. You can put LT1 parts on and in a Gen 1 engine you just need to plug the reverse flow cooling ports on the heads and add a distributor location for the intake.
I will be checking the size against my seats and with my head shop before making this jump but the logic sounds good in my head. Any experience with this would be appreciated. So about the LT1 heads on an L98. Some of you know its possible but I will be covering it in greater detail when I have pictures to show it. You can put LT1 parts on and in a Gen 1 engine you just need to plug the reverse flow cooling ports on the heads and add a distributor location for the intake.
Last edited by Space387; Jan 2, 2020 at 06:26 PM. Reason: Forgot something
Thread Starter
Racer
Joined: Sep 2017
Posts: 452
Likes: 55
From: Marianna Fl
I have to buy valves not seats. If this wont work I'll stick to stock. I dont have the cam or heads to justify the larger valves anyway. The thought is to be as efficient with my existing parts.
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
LT1 heads use 1.94 intake valve the seats have been ground to fit that size. Sometimes you can go larger and avoid replacing seats. When valve seat on the outer edge, valve will fall. I'm guessing you are try to diy valve job. Unless less you have access to the proper equipment you can't. Depending on how valve fit guides the may need service also.
Safety Car
Joined: May 2001
Posts: 4,750
Likes: 1,642
From: Fairfax Virginia
I am not used to seeing people reducing size in the valves. I spent a lot of money having my heads accommodate "larger" valves when I paid to have the heads cleaned, ported and polished on my BB C3.
To make more power you need to be able to move more air through the engine.
Lapping a valve at home for a lawn mower is okay, getting all 16 valves "in" with a three or five angle valve job should be left to professionals.
Best regards,
Chris
To make more power you need to be able to move more air through the engine.
Lapping a valve at home for a lawn mower is okay, getting all 16 valves "in" with a three or five angle valve job should be left to professionals.
Best regards,
Chris
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Le Mans Master
Joined: Aug 2015
Posts: 6,090
Likes: 1,972
From: St. Charles MO
Smaller valve /= more flow. That's not how this works. I understand why you're thinking that, but it isn't accurate. At higher lift values, the larger valve's correspondingly larger seat means a larger total opening for airflow (or exhaust flow). At low lift values, the larger circumference around the perimeter of the barely-open allows a lot more flow. When it comes to poppet valves, bigger is nearly universally better.
Thread Starter
Racer
Joined: Sep 2017
Posts: 452
Likes: 55
From: Marianna Fl
Smaller valve /= more flow. That's not how this works. I understand why you're thinking that, but it isn't accurate. At higher lift values, the larger valve's correspondingly larger seat means a larger total opening for airflow (or exhaust flow). At low lift values, the larger circumference around the perimeter of the barely-open allows a lot more flow. When it comes to poppet valves, bigger is nearly universally better.
This all came about from an article I found about guys throwing 1.94 valves in 305 heads (1.84) without a bigger seat and claiming gains but actually showing less in airflow from 0.05 through 0.4" of lift(-8cfm) Only at 0.5" did you see gain of +2cfm.
i can understand the flaw in a valve too small for the port causing mechanical failure but I fail to see the logic of bigger valves in the same port some suggest.
Final note, my heads are going to a professional to be cleaned, milled and have the valves lapped when I finish the port job on them.
Last edited by Space387; Jan 4, 2020 at 02:24 AM.
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
Years ago 305 heads on a 350 was a popular idea. Small cambers and cams with up to 5k RPM. The increased compression was the real benefits. The problem is the heads are designed for the small bore 305 and 262. The chamber is narrower result of smaller cylinder diameter. Even so, article referenced was installing larger valves.
I wouldn't be lapping valve, but then then again I wouldn't be installing LT1 top end on a SBC. In the process of the multi angle valve job, 3 angles are usually required to get valve to contact seat in the correct location. When adding additional angles can increase airflow.
I wouldn't be lapping valve, but then then again I wouldn't be installing LT1 top end on a SBC. In the process of the multi angle valve job, 3 angles are usually required to get valve to contact seat in the correct location. When adding additional angles can increase airflow.
Last edited by Kevova; Jan 5, 2020 at 11:34 AM.
Le Mans Master
Joined: Oct 2002
Posts: 7,098
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From: Las Vegas - Just stop perpetuating myths please.
Well I can't tell you if a seat of a 1.94" valve can be changed to seal with a 1.84" valve. But your cylinder head shop will be able to tell you what they can and can't do. I imagine it will sink the valves somewhat when they re-cut the valve angles. But if your asking will it increase flow I have to say no because the new valve angles for a smaller valve will seal with a smaller radius/diameter. That's kinda the reason for using larger valves is they open up the seat area increasing flow. Now larger valves can have issues with shrouding the valve against the chamber wall and flow swirl into the chamber meaning quality of flow also is affected but those are another topic themselves. What I think you considering as the old 305 head on a 350 trick (as mentioned) loses flow when valves increase from 1.84" to 1.94" - at least the power produced is lessened.
Save your money and use the stock 1.94" valves. I think it would be cheaper to re-contour the chambers for better flow - polish them too and reduce sharp edges that can cause pre-ignition. I don't like those squared blocks near the spark plugs.
Save your money and use the stock 1.94" valves. I think it would be cheaper to re-contour the chambers for better flow - polish them too and reduce sharp edges that can cause pre-ignition. I don't like those squared blocks near the spark plugs.
Le Mans Master
Joined: Aug 2015
Posts: 6,090
Likes: 1,972
From: St. Charles MO
I guess I'm not following: I don't see how you're going to get a 1.84 valve to fit in a 1.94 valve seat. If it can be done at all, then as cardo0 said it would sink the valve deeper into the pocket, which must means you've effectively lost valve lift (i.e. the smaller valve will be a lot more in the way of the seat area than the 1.94 valve would have been). The bottom line is that if you use a 1.84" valve, then at some location in the valve seat area there will have to be a seat with the correct diameter for that smaller valve, and that means that there will be less seat circumference to help low-life flow. You can't seat a 1.84" valve in a 1.94" hole.