Help with Mid Engine Design

[Matra et Alpine]

Biggest advantage is the ease of valve timing adjustment with seperate verniers on inlet and outlet.
OHV needs to have dual cams in block to achieve that.

[Matra et Alpine]

no we gave up rebuilding the A40 Farina Monte replica ... too much missing metal and not having the car ready we both did different things.

Been competing in the Scottish Sprint and Hillclimb Championship.
Check our youtube/facebook.
Sitting 2nd in class.
Finished 2nd in class in the Scottish Highland Speed Championship.

All was going well in the RX-8 till I had a big "off" last weekend
All OK to run again this weekend !!

[culver]

Well I completely agree with you both, but when you build a vehicle, at least in my mind, cost, dependability and ease of maintenance are key factors.

The problems with the OHV engine seem pretty serious, random at times and require monetary as well as back aching attention...obviously this depends on the precise model.

But standing on my original decision of buying an OHC engine from a well known crate engine supplier directly from the United States can be worth it in costs and time in the long run. You would be spending more time on the road and less time in the garage searching and ordering parts from a minuscule amount of suppliers.

The problems were hardly unique to OHV engines and they are not related to the engines being OHV. Furthermore, they only applied to a few versions of the engine. The early LS1s with piston slap would date back to ~1997 and 1998. The head issue was with a truck specific version and we have no information on how common it was. You are certainly concluding a mole hill is a mountain. Using this limited evidence to claim there is something wrong with OHV engines is very flaky.

Do also keep in mind that GM's got a very good crate engine program and the support and knowledge base for their engines (both OHV and OHC is extensive). Also keep in mind they aren't the only good option and depending on the application other choices may be better. The Audi 1.8T out of a B5 platform car for instance has a transaxle that nicely plops into a mid-engine configuration. Conversely, the LSx motors were almost always FR setups so you can't keep the whole powertrain in the family with that motor. A common setup seems to be the LSx + Porsche transaxle.

[Matra et Alpine]

Good job on the second place. Hill climbing always intrigued me because of the constant mix of high and low ratio gearing mixed with power and high rpm per section.

Scottish hills are particularly tight and twisty and short relative to European climbs. So gearing and power delivery are key to getting a winning machine. Winner in my class has a Rover 25 with a JUDD ex-BTCC engine and short diff

What type of differential and transmission pairing do you use?

I race in "standard production class" so it's as it came from the factory.
Sadly the RX-8 didnt' have many options so little scope to swap in different final ratios

and LOL on the "off"...any pics?

Worse ... video .... http://www.ultimatecarpage.com/forum...5&postcount=56 might get some pics once it's out of the garage after resetting the suspension tonight

[Matra et Alpine]

Drink the night before may have been contributory .... sharing malts is a tradition for weekend events Went out an hour later and posted my fastest time. It's only a car and it's racing, shit is ALWAYS gonna happen -- or your not trying hard enough !


Yeah well the dates are there once in the thread and if it's stuff that's off-topic of the original thread then we do tend to direct. But apart from this little digression, it's been pretty much on the same stuff as then and we kinda rely on folks reading the dates themselves.

[culver]

In my defense, it is not really limited evidence when it is commonly known and published.

As for how common; http://www.pistonslap.com/tsb.htm. As for the problems, they require serious attention and a pocket book (replacing pistons, cranks, and heads).

I am not claiming something is wrong for all the OHV engines. Several times I mentioned "precise models". Not all. Since I do not know the bloke who started the thread, by initial advice was to avoid them just so he can avoid any hassle because if someone has an OHV engine and needs to sell it AFTER it is rebuilt, they are possibly going to mislead someone in thinking it is a Corvette engine because of the misnomers surrounding all other OHV engines because of the mistake they initially made.

I think you will find that most engines that have been produced in the same volumes as the LSx family (including the truck and other variants which aren't labeled as LSx) will have some documented problems. The fact is these are VERY good motors and to avoid them if they are otherwise task appropriate is silly. More so to recommend someone else avoids them based on the limited information and knowledge you have presented is also quite silly. If you want to come up with a list of motors to avoid I think there are others that would be higher on the list than the GM small blocks.

Perhaps these guys could answer any of your specific concerns.
Chevy | Camaro | Firebird Reviews, Performance Parts, Modifications - LS1Tech.com

[culver]

I am simply challenging the notion that for reliability reasons people should avoid OHV motors. That idea is not well supported and the information contained in the Wiki hardly provides any sort of conclusive proof that even the GM small blocks should be avoided nor does it show that alternative motors will be less problematic. All I'm looking for is a show of the logic behind the post thus others can make better use of the information you have presented. It's not a mater of being for or against as requesting facts to back the statements.

[culver]

Here;

http://auto.howstuffworks.com/camshaft1.htm

They even provide colourful pictures and animations.

I don't think the question is "what is a camshaft". I think the discussion was, did you present sufficient evidence to back your statement that OHV motors should be avoided. So far, at best, we know we should avoid some versions of the Gen 3/4 SMC. You haven't shown we should avoid any other OHV motor.

[csl177]

Well in all fairness, I am entitled to my own opinion as are you...

Being that I posted my opinion in this seven 7 year old thread I think that that was a mistake...even though it was bumped recently by someone and they should have just made a new thread with a link to this thread.

I made a simple statement that needed a complex answer that people want to debate. I have backed up what I stated with links and so forth that they themselves can read and derive information and knowledge from...but I still cannot figure out your loyalty to OHV. I am not sure if it is directed at brand loyalty or what exactly.

Oy... it has nothing to do with loyalty, and the most recent posts to this thread are from June 2011.
"Simple" is an accurate description of your statement. Complex answers had been previously provided.

But again, to each their own. I stated why to avoid them, if someone chooses otherwise its up to them. I cannot be bothered to debate this anymore.

You haven't "debated" at all. I asked for an explanation which you haven't provided. You can't, because your declaration was false.

It did provoke some hilarious two-steppin' though:

For fun I am going to post this link again but without the link to the limitations section so individuals can read for themselves and come to their own conclusion.

http://en.wikipedia.org/wiki/Overhead_valve



I will also post the link to which I am suggesting so I am not just bashing a particular type. This I apologize for. I should have posted a link to which I support.

http://en.wikipedia.org/wiki/Overhead_cam



And I think we can let other individuals come to their own conclusion instead of us beating a dead horse. I think we can both agree on this.

No, you posted a blanket supposition. For fun, How Stuff Works and Wiki are not engineering sources and relate in no way to the
question of what engine type is best for a mid engine layout. I've been a member of SAE for over 30 years. If in the course of conversation a fellow professional made a declaration as overreaching as yours regarding a TYPE of mechanical system (and not a specific EXAMPLE) without supporting data, he/she would never hear the end of it. A more reasonable "opinion" would be that OHV engines have inherent limitations of volumetric efficiency related to rev limits and displacement; given similar parameters OHC engines CAN be somewhat more efficient.

The drivetrain layout has no bearing on the choice, only budget and application does.

You began this little escapade with:

Well I have to say DO NOT go with OHV. I have not read everything everyone wrote because I will be here forever and I think it is more suited for you to make the appropriate final decision based off of what we say.

Remember OHC not OHV or else it will be the most expensive mistake you'll ever make.

I suggest that next time you read the entire thread. Opinion is useless without information, and blanket statements are rarely accurate.

[culver]

M,
The simple facts are you posted an absolutism that OHV motors should be avoided because they will require expensive maintenance. The evidence you presented was poor and even if it applied 100% to all GM gen3 and 4 small block V8s it STILL would be poor as those aren't the only OHV engines available. Please don't get mad at me for questioning your statements when they the statements themselves are wide open for questioning.

[csl177]

No point rationalizing with M acting a twit, culver. He just showed his ass and took the inevitable course expected when called out.

[clutch-monkey]

Good point...but those are racing teams working with top of the line materials that are being changed every race (I am pretty sure).

awesome evidence captain persuasive