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New Heads and 1.25 Rockers?
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mikelars
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PostPosted: Sun Sep 05, 2021 11:51 am    Post subject: New Heads and 1.25 Rockers? Reply with quote

I have a question about my engine - I believe I may have bottlenecked my 1904 build by using Stock DP Heads (AA 500 casting).

I have a 1904 (74x90.5) with dual Weber 40 IDF, a 218 cam, performance 1 1/2 heater boxes and a Vintage Speed Superflow muffler.

I only have 1.1 rockers and 35.5/32 valves, DP, no porting. I feel like I might have 85 HP max but this is just a total guess based on driving feel.

My question is this - if I change to Panchito 40/35 heads and 1.25 ratio rockers, leaving all else the same, will that give me what the Dyno App was suggesting which was 112 HP. Seems like I would have to drop about $900 in order to upgrade - but wanted to see if anyone had any thoughts on this combo?
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UK Luke 72
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PostPosted: Sun Sep 05, 2021 11:59 am    Post subject: Re: New Heads and 1.25 Rockers? Reply with quote

Probably better having some proper port work done on those heads assuming it's for that split.
Alstrup and Brian E are the guys you want to look out for Smile
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PostPosted: Sun Sep 05, 2021 12:33 pm    Post subject: Re: New Heads and 1.25 Rockers? Reply with quote

Hello.
An engine like the above mentioned should pull about 100-105 FWHP which is roughly 85 WHP.
IMHO AA500 heads are generally reasonably good. However, there are speciments out there which has a horrible valve job. That alone can easily kill 10 hp. - Generally all AA heads can benefit from a better valve job.
If your version of the 500´s are of the ones with a poor valve job you will not gain much with adding 1,25 rockers because the port energy is on the low side. Also, if the 40 IDF´s have the stock 28 mm venturies in they will give you a natural flow restriction. (In the right combo 28 mm venturies can support over 120 hp, but the set up needs to be rather efficient)
If you go with a set of dual springed P heads, 9 to 9,2-1 and 1,25 rockers and replace the venturies with a set of 32´s you have a 130 hp potential. It will want to rev, and rev to about 6000 peak power. If you set it up well you will soon be in the 180-185 Nm peak torque range.

Detailing the AA500´s is of course also an option. Done right it will give you more lower rpm power at the cost of approx 5 hp on top.
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mikelars
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PostPosted: Sun Sep 05, 2021 12:37 pm    Post subject: Re: New Heads and 1.25 Rockers? Reply with quote

Yes - it is for my 1966 Split. But why is the porting on 35.5/32 with 1.1 rockers better for a bus than getting the 40/35 with 1.25 rockers?

I am assuming it is because low end torque is better for a bus than high rpm HP?
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Alstrup
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PostPosted: Sun Sep 05, 2021 12:52 pm    Post subject: Re: New Heads and 1.25 Rockers? Reply with quote

I don´t think anyone said it was better. It is more a matter of what you want. Also, the reason to why the P heads work so reasonably well out of the box is that the ports are conservative in volume which along with a good port shape delivers very good port velocity and thereby port energy (When the combo is just reasonably right) so they will support both good power across the rpm range.
1900 cc is just around the point where I personally am beginning to lean towards larger than stock valves, but again dependant on what the engine is to be used for and the behaviure needed.
for comparison. Here is a dyno chart from a 1914 buggy engine with big wheels etc. Here it was important that the engine would haul butt rom just over idle and be able to cruise at 2200 rpm (50 mph) and pick up in 4rth. So here I chose a set of Nice 113 heads to get the port I wanted and the cam needed to help make the engine do as the customer wanted.
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Paul.H
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PostPosted: Sun Sep 05, 2021 1:36 pm    Post subject: Re: New Heads and 1.25 Rockers? Reply with quote

mikelars wrote:
I have a question about my engine - I believe I may have bottlenecked my 1904 build by using Stock DP Heads (AA 500 casting).

I have a 1904 (74x90.5) with dual Weber 40 IDF, a 218 cam, performance 1 1/2 heater boxes and a Vintage Speed Superflow muffler.

I only have 1.1 rockers and 35.5/32 valves, DP, no porting. I feel like I might have 85 HP max but this is just a total guess based on driving feel.

My question is this - if I change to Panchito 40/35 heads and 1.25 ratio rockers, leaving all else the same, will that give me what the Dyno App was suggesting which was 112 HP. Seems like I would have to drop about $900 in order to upgrade - but wanted to see if anyone had any thoughts on this combo?

I'd say leave it alone until something goes wrong with it.
I just went the other way with my 1904cc by taking off the ported big valve CB044's and 45mm throttle bodies , too revvy and noisy for a bus replacing them with some stock VW heads and a single point injection
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mikelars
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PostPosted: Sun Sep 05, 2021 6:31 pm    Post subject: Re: New Heads and 1.25 Rockers? Reply with quote

Paul H,

When you say your 1904 was too noisy and revvy for a bus - do you mean that the 40/35 valves in the Panchito 44s make the engine a lot noisier by itself? I was going to use Panchito 44s and 1.25 rockers - but am interested to know how much noisier it makes it. I already have the VS SuperFlow, and was thinking the heads would only slightly add to the noise.

Also, what do you mean by “revvy” - does it rev up a lot more easily, or do you need to rev it higher to get to the power zone?

I have a 3.44 pinion in my transaxle, and want more power for my 4th gear - which is 3100 rpm at 65mph…. But I also want a somewhat quiet bus…
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Brian_e
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PostPosted: Sun Sep 05, 2021 9:05 pm    Post subject: Re: New Heads and 1.25 Rockers? Reply with quote

You need some really good 37x32 ported heads, or do some work to yours.

I build 74x92 1968cc bus engines with a web 218, my 37x32 heads, 8.8:1, 1 1/2” header and 40mm IDF’s. They are great bus engines and have lots of low end power.

Adding the bigger 40x35 valves but keeping the cam the same will most likely kill off some of your low end power, and only increase the top end marginally.

I agree with Torben, the 1904-1968cc range need slightly larger than stock valves with efficient, high velocity ports. This range of engines meant for a bus aren’t quite big enough to fully utilize a 40x35 head.

Check out Steve Tims ports super stock heads.

Brian
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PostPosted: Mon Sep 06, 2021 2:28 am    Post subject: Re: New Heads and 1.25 Rockers? Reply with quote

mikelars wrote:
Paul H,

When you say your 1904 was too noisy and revvy for a bus - do you mean that the 40/35 valves in the Panchito 44s make the engine a lot noisier by itself? I was going to use Panchito 44s and 1.25 rockers - but am interested to know how much noisier it makes it. I already have the VS SuperFlow, and was thinking the heads would only slightly add to the noise.

Also, what do you mean by “revvy” - does it rev up a lot more easily, or do you need to rev it higher to get to the power zone?

I have a 3.44 pinion in my transaxle, and want more power for my 4th gear - which is 3100 rpm at 65mph…. But I also want a somewhat quiet bus…


Most of the noise is from the induction and there is not much you can do about it and when you start applying the usual tuning techniques sure you can make more peak power but it shifts everything up the rev range and hurts the low end where you drive most of the time. The unknown quantity in my current research is how larger valves and ports effect the low end and how mild I can go with the cam when used with a stock 1600 PICT manifold
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PostPosted: Mon Sep 06, 2021 2:41 am    Post subject: Re: New Heads and 1.25 Rockers? Reply with quote

The panchito heads are GREAT, BUT 92x78 is about the smallest engine I'd want them on
.....for general street use
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PostPosted: Mon Sep 06, 2021 2:48 am    Post subject: Re: New Heads and 1.25 Rockers? Reply with quote

modok wrote:
The panchito heads are GREAT, BUT 92x78 is about the smallest engine I'd want them on
.....for general street use

I haven't seen any of those yet but I like the look of them and the matching manifolds
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Alstrup
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PostPosted: Mon Sep 06, 2021 8:38 am    Post subject: Re: New Heads and 1.25 Rockers? Reply with quote

modok wrote:
The panchito heads are GREAT, BUT 92x78 is about the smallest engine I'd want them on
.....for general street use

I have used them right down to a mini stroker (76*87) with a C35 cam, installed on 106 ILC, 9,3 CR. 1,25 rockers, 123 bluetooth distributor, a CSP super Comp and fed with a set of 40 Dellorto´s. It runs better overall than the parts suggest. It - is - a tad soft under 2200 rpm, but a custom timing curve took care of some of that. After that it hauls very well up to about 56-5700 rpm. and flattens off from there. This engine is not dialed in yet, but I would not be suprised if it shows 125 hp and 175 Nm. I couild have made trhe same with a set of detailed stock valve heads, but they would have been more expensive than an off the shelf solution.
An 1835 bus engine can easily be set up to work vewry well with such a set of heads. Its just a matter of chosing the right cam, exhaust and induction. But from an avberage standpoint my first choice would also be smaller valves to keep the port volume down.

That said, bus engines with modified stock carburettors are getting increasingly popular over here at least. Partly for easier noise reduction, but even more for the somplicity of a "stock" carb. Our 80 hp 1835 and 100 hp 1955 cc. are very popular. My new and very detailed 120 hp 2165 is sloooowly picking up.
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PostPosted: Mon Sep 06, 2021 10:52 am    Post subject: Re: New Heads and 1.25 Rockers? Reply with quote

I am trying to understand why larger valves and rockers would hurt the lower range (say, 2000-3200 rpm) compared to stock valves and rockers? I would have thought the low end would also breathe better and pull in more from the carb - especially if I move to a 32 venturi and 1.3 main jet from 28/1.15.

I do like the low end torque, so I don’t really want to make the low end weaker…
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PostPosted: Mon Sep 06, 2021 11:01 am    Post subject: Re: New Heads and 1.25 Rockers? Reply with quote

Like I vaguely mentioned above, your displacement is in "the grey zone" The answer to your question is port velocity and thereby port energy at X rpm. The P heads do a very good job overall, and in your case the loss will be minor if you will even notice it compared to out of the box AA500´s. What IS important is that you get the squish right. The better the squish and ignition timing you can get/make the less you will notice it.
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PostPosted: Mon Sep 06, 2021 11:04 am    Post subject: Re: New Heads and 1.25 Rockers? Reply with quote

mikelars wrote:
I am trying to understand why larger valves and rockers would hurt the lower range (say, 2000-3200 rpm) compared to stock valves and rockers? I would have thought the low end would also breathe better and pull in more from the carb - especially if I move to a 32 venturi and 1.3 main jet from 28/1.15.

I do like the low end torque, so I don’t really want to make the low end weaker…


Yes this is what I'm going to find out.I have another engine which is a 2017cc 78.4x90.5 with 42x37 valves and a really mild cam, stock pushrods. I haven't tuned it in properly or had it on the dyno but it pulls like fxxx. In fact it pulls so hard that the oil light comes on so need to put a deep sump on it. It sounds
very nice without the induction noise
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PostPosted: Mon Sep 06, 2021 11:14 am    Post subject: Re: New Heads and 1.25 Rockers? Reply with quote

Ok - that sounds reasonable - can you explain what the squish is, and how I can best attempt to get it right? Do you mean with the air squish of the carb velocity stacks or the cylinder compression squish?

I have 59cc chambers on the AA500s now, so the Panchitos at 54cc or 57cc (seems like they changed the default at some point?) would lead to just slightly higher compression for me…

I am still thinking Panchitos 40/35 with dual springs and 1.25 rocker arm upgrade. With this, the 32mm venturis for the Weber 40 IDF, and I calculated the main jet to be 1.3 with this setup.

My AA500s are running fine, but I need a project this Fall anyway, and I would love to be able to have a bit more power - given I have stock bus gears but with a 3.44 pinion - which is fantastic actually even with my current HP…
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PostPosted: Mon Sep 06, 2021 11:16 am    Post subject: Re: New Heads and 1.25 Rockers? Reply with quote

1.25's with a WEB 218 might be a little harsh on the valve guides
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PostPosted: Mon Sep 06, 2021 11:21 am    Post subject: Re: New Heads and 1.25 Rockers? Reply with quote

Does anyone use 1.25s with a 218? I don’t mind a bit more wear, but I mean some people have 1.3 and 1.4 rockers. Many posts say 1.25 doesn’t really do that much over 1.1 - so I just wanted to combine 1.25 with the larger valves since I can get dual springs for $22 more….

Does harsh mean the valve train lifespan will be really short? So far I have 10k miles on really clean oil with full flow - so I was going for long engine lifespan….
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PostPosted: Mon Sep 06, 2021 11:25 am    Post subject: Re: New Heads and 1.25 Rockers? Reply with quote

Harsh as in hard on, will cause more wear, shorter lifespan. yes there is 1.3-1.6 ratio rockers out there, but the cams for them are ground different for them.
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PostPosted: Mon Sep 06, 2021 11:31 am    Post subject: Re: New Heads and 1.25 Rockers? Reply with quote

As long as it isn’t a red flag to use a 218 with 1.25 rocker arms? I suppose I could always easily compare 1.1 with 1.25 and only leave the 1.25s on there is there is a nice benefit to them…
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