Headwork

[Blue Supra]

Hey lads,

Im going to be taking my datsun engine head in to be checked over, reground etc but what can I get them to do whilst its there that will help the engine? Like, im building an engine and have NFI what im doing yet

Ive heard terms thrown around like "port the head" and other stuff but ive got no idea what any of it means.

Please help enlighten me

[P4g4nite]

The concept is simple enough. You want to make your engine more effiecient at pumping air, factory heads casting are generally rough, especially old models and this roughness makes a small, detrimental effect on air flow. So you grab a grinder and smooth out the passages.
You can also (if you have space) machine out the heads enough to fit larger valves.
You can 'deck the head', machine some height from the block to increase compresssion ratio.
You can also screw it up and make the engine less efficient than factory, make sure they have good experience at this thing before you pay them to ruin your motor.

What kind of engine is it? How much are you willing to spend? What other other modifications are you going to do to get the best out of headwork?

If you are just getting the head machined flat and aren't going to touch your intake or exhaust or stuff I wouldn't really bother wasting cash on expensive porting with dubious value.

[Blue Supra]

intake will be dual dellorto carbs through a cast manifold, exhaust is through 4-1 headers and 2" exhaust on a 1.8L 4cyl datsun L18 motor.

Im not keen to spend over $500 on this but ive been quoted about $80 by a head shop to check it over, machine it and give it a good clean.

[hightower99]

If you aren't looking to use too much cash then you should stick to the easy stuff that you could do yourself (without messing anything up).

I would suggest that you at least match the manifolds (both intake and exhaust) to the ports in the head.

A few things to know:
Never polish the intake ports (smoothing out casting flash is fine).
Exhaust ports can be polished.
You can grind the intake valve guide so that it is close to flush with the port roof in the intake ports but you should never grind the exhaust valve guides.
Don't go crazy and try to open up the ports as much as possible this will kill charge velocity and hurt performance.
3 angle valve cuts, when done properly, can help alot.


Other than that make sure all the valves seat properly and make sure the head is falt and clean and you should be fine.

[charged]

A good port job basically blue increases the flow of the head, the more air you can get in there the more HP, this is done by sometimes reshaping the ports,enlarging, different valve angles, bigger valves etc. Also porting depends on what cam your running,valve overlap, lift etc. Are you putting a bigger duration cam in the car.

heres a good link mate that shows the basics of a good port job
porting secrets

[Matra et Alpine]

As by your own words you've NFI ... then do NOT do anything by yourself unless you have a ready supply of replacement heads or an expert to guide you. Too often the first attempt will end up opening up a water jacket
Especially given inappropriate guidance from "experts" -- come on ht, you should KNOW you cannot arbitrarily suggest that it's OK to flow the valve guide back flush On some engines you'll end up accelerating valve guide wear and introduce horrendous slop !!

Get a tuning book for the head in question. It should give all the suggestions fro doing everything from a Stage 1 - polish and mild port to Stage 4 - reshaping chambers

[hightower99]

Originally Posted by Matra et Alpine

Especially given inappropriate guidance from "experts" -- come on ht, you should KNOW you cannot arbitrarily suggest that it's OK to flow the valve guide back flush On some engines you'll end up accelerating valve guide wear and introduce horrendous slop !!

I wasn't telling him to do that. It was more to make the point that you can grind the valve guides down abit on the intake side whereas you should never grind the valve guides on the exhaust side. It was just a piece of advice because I have seen that some tuners actually grind the valve guide on the exhaust side as well.

The relatively easy stuff like matching the manifolds to the head and possibly cleaning up the ports abit (not opening them up but smoothing casting flash) should be achieved without any troubles.

[Blue Supra]

Yeh I wont be doing this stuff myself. Ill be giving it to a shop to deal with but yeh, wanted to know what sortof options there were and their benefits.

Not sure on the cam at this stage charged. depends what the budget allows.

[Matra et Alpine]

Originally Posted by hightower99

I wasn't telling him to do that.

Originally Posted by original hightower99

If you aren't looking to use too much cash then you should stick to the easy stuff that you could do yourself (without messing anything up).

I would suggest that you at least match the manifolds (both intake and exhaust) to the ports in the head.

A few things to know:
Never polish the intake ports (smoothing out casting flash is fine).
Exhaust ports can be polished.
You can grind the intake valve guide so that it is close to flush with the port roof in the intake ports but you should never grind the exhaust valve guides.
Don't go crazy and try to open up the ports as much as possible this will kill charge velocity and hurt performance.
3 angle valve cuts, when done properly, can help alot.


Other than that make sure all the valves seat properly and make sure the head is falt and clean and you should be fine.

Is there a magic pixie altering your posts then ?

Clearly your message DOES suggest doing it.
YOU know what's easy/hard but BS can't

[charged]

Originally Posted by Blue Supra

Yeh I wont be doing this stuff myself. Ill be giving it to a shop to deal with but yeh, wanted to know what sortof options there were and their benefits.

Not sure on the cam at this stage charged. depends what the budget allows.

I would suggest a fairly mild cam for your first engine Simon, if you build a hypo revving 4cyl na motor with big cams and a narrow powerband you will need a close ratio box also. Get the first engine built nice and mild so its reliable and easy to use. As you get faster then the next development stage can happen.

Matra have to agree with you, very short valve guides equals trouble at 9000rpm

[Blue Supra]

Well that leads into my next question. Cams. Whats the story with cam angles and grinds and what not? Like i understand some cams are better for revs some more for torque but i dont understand when someone says for example:

"I have a 72 degree cam" (i dont know if thats real or not) but yeh, whats the story there?

[Matra et Alpine]

Get down to the library or a second hand book store and get any of David Vizards tuning books from the 70/80s. Talks through all of this from a DIY angle. We shaped and ported the Mini 1275 heads based on his guide. Many of the ideas presented don't work for modern engines, but he always went through all the math and engineering.

[Blue Supra]

Ive ordered a book on my engine specifically. (Datsun L series engine) that goes through everything but just wanted a bit of basic background before i sink myself into that.

Thanks for the knowledge guys!

[jugga]

Originally Posted by Blue Supra

Well that leads into my next question. Cams. Whats the story with cam angles and grinds and what not? Like i understand some cams are better for revs some more for torque but i dont understand when someone says for example:

"I have a 72 degree cam" (i dont know if thats real or not) but yeh, whats the story there?

a change in cam profile will increase valve lift (how far it opens/goes into the chamber) increasing volumetric effiency (more charge into chamber). Also the degrees/timing influence how long/when the valves open. typically a race cam will have more overlap to road cam. overlap is when the intake and exh are both open. this is useful for scavenging which is cause by the exh gases leaving. teh proces goes like this, exh open - gases escape, int opens with exh still open - the space left my exh gases sucks in the charge, alot faster than normally. this improves performance due to the better efficienct at high revs.

now you can wake up or tell me where im wrong ha

it is definately right to sort out the air/gas flow before cams. polishing ports is a good idea but depending on manufacture there will be a limit to what you can do. it will also make sure u get the most out your cams. injectors and valve train etc may need replacing depending on how lumpy and raw you want i to be.

engines doo sounds nice and raspy once there flowing nice.

[johnnynumfiv]

Originally Posted by Matra et Alpine

Get down to the library or a second hand book store and get any of David Vizards tuning books from the 70/80s. Talks through all of this from a DIY angle. We shaped and ported the Mini 1275 heads based on his guide. Many of the ideas presented don't work for modern engines, but he always went through all the math and engineering.

That man is a genius, I highly recommend picking a copy up bluey. I would think that his theories would work with other older engines such as the L series.