Max HP/TQ with 1 3/8" header and STOCK heater boxes?

[Zach Gomulka]

What is the most hp/tq you could make while keeping the stock heaterboxes and a 1 3/8" header? I would also assume you would want to use stock 35.5x32 valves as well... a stock heaterbox and 1 3/8th's would bottle neck a large exhaust valve, overly heating the head and causing failure (cracks), right?? Would there be a displacement limit as well?? Trying to stuff two liters plus of exhaust down a stock valve, heaterbox, and 1 3/8" header sounds like a recipe for disaster in my mind...

For the engine builders: What engine would you build for max hp/tq if the only requirements were that it retain the stock heaters and 1 3/8" header??

Edit:
I meant for this to go in "Pure Racing" Could you move it for me?? Thanks

[Torben Alstrup]

Hello.
120 hp out of stock heaterboxes and a 1 3/8" header is about what you can squeeze out of it on street engines, without having to go into split cams T4 style. The other thing you have to be aware of is head temperature under load. Around town and a few blasts now and then is not the problem. Sustained left lane powerloads is.
I have built a couple of 1776és around stock heads and stock heaterboxes + a relatively aggressive cam. (300ish) They have made 115 - 117 hp and 170 - 180 NM torque.
But it is mandatory that the engine has a good supply of fresh air (as in all hipower cars) decklids w/o vents and a sealed engine compartements are a nono.
T

[Zach Gomulka]

Thanks for the reply!!! You give me hope!

So this is my ultimate plan, please give me your opinion on it...

88x82 (1995cc)
Biral cylinders
EMPI 831 cam... 290 total duration, .447" @ valve
stock valve ported heads
8.5:1 CR, 1.5mm deck
dual Solex 40P11's (32mm venturis)
1 3/8 header and stock 'boxes, of course

Will be backed by a 5 speed (that will come before the motor)
4.12 r+p, 3.78, 2.25, 1.48, 1.04, .82

The car is a '72, so it has great factory cooling, but I will make it much better

My goal is to have the ultimate in reliablility and longevity. Something that I could get in, flick the key, and drive across the country without too much hassle. A very under stressed "lazy" motor, but I would still like to see 122hp and 122tq at the flywheel.

Possible?

[Torben Alstrup]

I do not know that cam, so I really cant comment on that. I have never really been an "Engle cam" guy, but in this case I actually think that a W120 would suit your needs. I would decrease the deck to 1,1 mm (unless it´s cast crank) and bump the CR to 9 - 1.
I´m not sure that you will see 122 hp, but the torque oughta be there, and widespread too.
I assume that you will use stock length rods.
T

[Zach Gomulka]

Its an original EMPI cam, it looks to be right in between a 110 and a 120, with a little more lift.
Deck height will be 1.5mm maximum, 1mm minimum.
The rods will be Porsche 912 (136mm)
The crank will be a VW forging, counterweighted and stroked.

So you think this will actually work well??
Thank you for the input!

[Torben Alstrup]

Desspite of what many say, deckheight has a lot to do with temperature, even in the 1 - 1,5 mm range.. You are using birals, which are very good wrt heat dissapation. That means that you can afford to go significantly closer to the limit of the fuel octane you will be using, especially if you keep the tolerances down.
With that short a rod, I would definitely not go lower than a W120. You need duration to keep the airflow up, so the rpm range and peak power is up where its fun. And you will definitely see lesser numbers if you skip on that point.

I dynoed a 2007 T1 a couple of years ago,(a customers vehichle) with very mild 041 heads, 8,5 cr, W110 cam, 40 IDF/32 venturies and a regular 1½" header and a home made phat boy. It pulled 110 hp @ 5000 rpm and 160 NM max torque at about 3000 rpm. (I forgot the exact point) It ran nice, idled very well, but it was kinda lazy. I would have bumped the CR and gone 1 cam group up. and I dont even think it would have hurt bottom end power in a noticable way. It would just have made the engine much more "alive"
T

[Zach Gomulka]

I wish that I had a little more flexibility on the cam, but I don't. Since this engine is going in an EMPI GTV, I want to use as many original EMPI parts as humanly possible. The next cam group up has a whopping 322 degrees duration!

I will get the deck height down to 1.0 or 1.1mm, and raise the compression slightly to about 8.7-8.8. I am hesitant to go higher because the best fuel here is only 91 octane

With the nicely spread out 5 speed gearing and a flat torque cuve, I am hoping that this will be one fun driver

Thank you so much for your help!!!