My son and I are restoring a 1970 Mach1 which came with a 351C 4v. I currently have a 429 cobra jet. The 351C came in parts with the car, it needs to be totally rebuilt. The 429 has just been rebuilt. The question I have is should I stick with a matching engine or use the 429? Will putting the 429 in adversely affect the value of the car later?

Thanks
Rick

 

Rick, don't switch engines. The 429CJ was never offered in the 69-70 Mustangs. For the big blocks in 1970 only the 428 and Boss 429 were production options. Your 351C 4V with matching serial #s will be much more desirable, accurate and valuable in that 70 Mach1. Plus that 351C is a great power plant. If you're looking for more bolt on HP, try using 1971 Boss 351C parts or get rid of the cast iron intake, exhaust and Autolite carb and go for tubular headers, Ford Muscle Parts alum intake (or aftermarket) and Holley carb. See this website for more info
http://www.muscularmustangs.com/database/1970.php

 

It comes down to budget and power and how the car will be used.

 

I'd say stick with the 351c and rebuild it. If the engine is original to your Mach 1, you should definitely put it back in.
Save the 429 for something else.

 

Thanks for the advice. Looks like I will be rebuilding the 351C.
I have read that the 4v heads are designed to produce the high torque around 7000 rpm.
If that is true, what changes should i make to get better performance at lower rpm as I do not see much of an opportunity to reach 7000 rpm very often.

Thanks.

 

Rebuild it with a 408 rotating assembly at 10.5:1. Drops right into the block.
Rebuild the heads to get rid of the two piece valves.
Put in a dual pattern cam to hold the exhaust open a little longer and keep it around .060 lift.
Run under 12 all day long at the track on pump gas and have a screamer on the street.

 

For what you want, you'll need 2v heads. You can pretty well name your price on the 4v or keep them for future hotrod use, but they just don't work as well at lower RPMs. An intake intended for 2 v heads has smaller runners and will bolt to the 4vs, but this is a hack although it should improve low end a bit due to reduced intake volume/higher velocity.

 

Do not!!! swll thosw heads and DO use them. Get a real great exhaust system, work that suspension over and If your compitant driver and do not go high 11's I will personally buy your immediate family a feast at Red Lobster. Honest!.we raced those cars on the 70's, the clevland 4v heads are the absolute best ever made and were never ported, just gasket matched, even by the glidden's. Well known fact, they are the best. And stock, so yes, with the factory style intake and the right holley carb they will be perfect for the street. Get the best exhaust you can find, have a real cam ground by someone good, ask for arizona @ racing head service, he if still alive will hook you up! just when having them re-done make sure and get the valve seats replaced with the new hardened ones, cause ya cant get real lead anymore and those soft seats will not last long, and won't hold a 3 not 5 way vale job for over 5-10k miles max.

 

I'm one of the few to say stick the Big Block in it. I really don't care about hurting any kind of future value, build it and run it, enjoy it.
Lynn

 

That's what I did!