What Are The Advantages of Pushrod Engines Over OHC?

[midnightbluS10]

If that's the case, where are all these dohc drag racing motors? If it's such a serious upgrade, wouldn't everybody be jumping on it?

[user-23911]

Because they're all smaller capacity and when it comes to turbos, they seem to excel.

Probably because a smaller bore will seal a HG better than a bigger bore,the bolts are closer together, that's when the pressures start to become really excessive.

[kimosabi]

Advantages push rod over OHC? It's hard to find one really from a power stand point. The moment you see a 2.0litre Cosworth YB DOHC make 800hp on pump gas you come to realize that.

[hoffman900]

If that's the case, where are all these dohc drag racing motors? If it's such a serious upgrade, wouldn't everybody be jumping on it?

In a real race class? Rules.

[user-23911]

Nothing worse than rules?



Just to make the slow ones faster?





No innovation?

[DaveMcLain]

The LS engine has the benefit that the same layout is used in the truck engines and in the high-performance car engines. The truck engines are iron block and the higher-performance versions are aluminum block, but the layout is the same, and stuff is generally interchangeable between them. You would know this better than I. (I don't do automotive V8 engines.)

But a Ford 4.6 SOHC 2-valve in a Crown Victoria, is a lump, and always will be. The DOHC 4-valve versions were rare (only in Lincolns and "special" versions of the Mustang) until pretty recently (2011-ish). The 5.0 in the F150 nowadays is DOHC 4-valve - but that's only since 2011.

And then there's Ford's infuriating habit of making the same-displacement engine in two different assembly plants with significant design differences between them so that stuff doesn't interchange. (I know GM is not innocent of this, either!)

LS engines that you can make into a monster are plentiful. "Mod motors" in the desirable DOHC 4-valve configuration ... not so much.

None of this has anything to do with pushrod versus OHC.

The Ford Mod engines have some weird interchangeability of parts. You could unbolt the single cam heads and bolt on the DOHC versions right onto your existing short block.

[hoffman900]

Nothing worse than rules?



Just to make the slow ones faster?





No innovation?

Yes.

In every race series where OHC multi-cylinder engines have to run against OHV 2-valve engines, the rules give the latter much more allowances in terms of restrictor size, boost, displacement, and/or weight.

No one could afford innovation except the OEMs.

[Brian P]

You don't see pushrod engines in Formula 1, MotoGP, World Superbike, World Rally Championship, etc.

NASCAR and certain drag racing classes use pushrod engines because, as mentioned above, the rulebook says "thou shalt".

I thought of one advantage. It's easier to change the head gasket because you don't have to mess with the cam timing.

[tt 383]

Honestly don't see a good, mass produced ohc v8 in the states at least that is worth the trouble of a swap or expense till maybe now with the coyote. Tuning isn't cheap for the foreign stuff like BMW, Audi, and to a lesser degree Toyota and Nissan. The aftermarket seems to be lacking and extremely expensive and it seems to me as power and cost go up, bugger form factors like BBC/BBF prove more capable/reliable and less costly over their life of teardowns and rebuilds. Add to the fact aftermarket fuel injection can be done on any engine you want now and the hurdles for ohc in cost/size/availability make it a "what for" proposition.

I also question that ohc "boost" better than others. Till you try them at the same bar it's unknown. Rules don't usually allow that though....

[tt 383]

Honestly don't see a good, mass produced ohc v8 in the states at least that is worth the trouble of a swap or expense till maybe now with the coyote. Tuning isn't cheap for the foreign stuff like BMW, Audi, and to a lesser degree Toyota and Nissan. The aftermarket seems to be lacking and extremely expensive and it seems to me as power and cost go up, bugger form factors like BBC/BBF prove more capable/reliable and less costly over their life of teardowns and rebuilds. Add to the fact aftermarket fuel injection can be done on any engine you want now and the hurdles for ohc in cost/size/availability make it a "what for" proposition.

I also question that ohc "boost" better than others. Till you try them at the same bar it's unknown. Rules don't usually allow that though....

[Walter R. Malik]

I have not read every post in this thread but, I would think that physical size is the only advantage a pushrod engine would have.

I loved the Northstar and Aurora engines but, they never got popular at all; unless you ran an INDY car.

EDIT: I actually road raced an Olds Achieva Quad-4 for a while.

[kimosabi]

I also question that ohc "boost" better than others. Till you try them at the same bar it's unknown. Rules don't usually allow that though....

In a V8 application you mean? Any inline engine the OHC and DOHC boost better.

[turbo2256b]

One reason the ford mod motors work best with boost is the port configurations. Poorly designed ports and runners improve best with something to force air through them.

I remember roush and ford got together to when the 10 cyl mod was aboutto go into production. we proved he 460 with mods more like were done on the 302 better intake exh it blew the 10 banger out of the water on performance , cost, packaging, power, ease of rebuild, economy. We were told to drive it into the drainage pond in front of the EEE building. reasoning politics ford is now about OHC roller follower engines.
Same with Jag we had engines that fit but had to design special heads with bucket tappets as that was their thing. The guy that set up the valve train on them goofed them up a bit causing a lot of dunage due to his limited ability to do stack ups correctly

[turbo2256b]

Also porting head would charge like 800.00 for a set of OEM ford , chevy, chrys heads with valve and spring upgrades. Mod 2 valve more like 1200.00 due to the pain of dealing with cam and other issue with flowing at different valve heights. More like 2400 for a 4 valve as it was like doing 2 engines. Also had to develop and have manufactured our own valves for the mod motors as aftermarket ones didnt do well

[ptuomov]

One reason the ford mod motors work best with boost is the port configurations. Poorly designed ports and runners improve best with something to force air through them.

Why so? Many people believe the opposite.

Although it's the case that if you're knock limited on pump gas, a poor port can be boosted over to a large extent by increasing manifold pressure until the knock limit is hit.